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coefficient for lens: really true?

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May 13, 2005 7:01:52 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Hi,
1.Is it true to say that if I use a 50mm lens from a 35mm camera on a
Digital SLR, I get the equivalent of a 75mm lens?
2. If the answer to question #1 it is yes, then is my subject getting closer
(as if I was using a telephoto) *and* the view angle getting narrower or is
it just the view angle getting narrower *without* the subject getting
closer?
Regards,
Jean.

More about : coefficient lens true

Anonymous
May 13, 2005 7:01:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"JD" <no.spam.jdon@wanadoo.fr> writes:
> Hi,
> 1.Is it true to say that if I use a 50mm lens from a 35mm camera on a
> Digital SLR, I get the equivalent of a 75mm lens?

Id depends on the camera.

If the sensor size for that camera is such that the multiplier is 1.5,
yes. If the multiplier is 1.6 as it is in some cameras, then that
50mm will have a depth of field crop that gives a coverage angle
equivalent to a full fram 80mm lens.

There are full frame dSLR's out there (I think, and if so, they're
certainly not in my price range) that don't have this property of a
multiplier.

> 2. If the answer to question #1 it is yes, then is my subject getting closer
> (as if I was using a telephoto) *and* the view angle getting narrower or is
> it just the view angle getting narrower *without* the subject getting
> closer?

The latter. The multiplier comes from the fact that the digital
sensor is smaller than the full 35mm frame size. It's really a field
of view crop rather than optical magnification. Picture shooting
onto a 35mm negative, but then only being allowed to use the center
area of the film rather than the entire frame.

Best Regards,
--
Todd H.
http://www.toddh.net/
Anonymous
May 13, 2005 7:01:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

The Kodak DCS Pro SLR/n (36mm x 24mm, +-$5000) and Canon EOS-1DS Mark
II (36mm x 24mm, +-$8000) both have full frame CCDs...

bH
Related resources
Anonymous
May 13, 2005 7:01:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Todd H. wrote:
> It does, but as folks are pretty prickly and correct to point out
> often in this forum, the visual effect of field of view crop is
> different than true magnification.
>

Now wait for the if-you-print-to-same-size crowd to jump at you ;) 

Comparing 35mm vs sub-35mm lenses reminds me of what I was doing today,
that is, checking all my lenses. In one hand, I held a Minolta 35-70mm
and in the other I held a Pentax Super Takumar 50mm f/1.4. The Pentax
M42 mount lens has a much narrower barrel than the Minolta or my Canon
lenses including the 18-55mm EF-S lens. Now wasn't sub-35mm sensor
technology supposed to deliver lighter and smaller lenses?

- Siddhartha
Anonymous
May 13, 2005 7:01:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"JD" <no.spam.jdon@wanadoo.fr> writes:

> 1.Is it true to say that if I use a 50mm lens from a 35mm camera on a
> Digital SLR, I get the equivalent of a 75mm lens?

No. Yes. Well, sorta. :-)

First of all, it depends on *which* digital SLR. The ones I can think
of off-hand have crop factors from 1x (none) to 2x. The entry-level
ones are 1.5x (Nikon D70) and 1.6x (Canon Digital Rebel).

So for those entry level cameras, the 50mm lens gives the angle of
view of a 75 or 80mm lens on a 35mm film SLR.

The *actual focal length* does not change; that's an attribute of the
lens, so nothing in the camera body can change it. However, the
sensor is smaller than a 35mm image; the sensor is positioned in the
middle of the image projected by the lens, so think of it as cropping
out the center part of the picture. (The viewfinders are corrected to
show what the sensor captures, so you don't mostly have to think about
this when using the cameras.) So for computations that use the focal
length (like calculating your own dept of field tables, or doing
exposure compensation for bellows extension, or whatever), the focal
length is whatever is marked on the lens.

> 2. If the answer to question #1 it is yes, then is my subject
> getting closer (as if I was using a telephoto) *and* the view angle
> getting narrower or is it just the view angle getting narrower
> *without* the subject getting closer?

The two are inextricably linked; your question makes no sense. Making
the angle of view narrower is precisely what a "telephoto" does, and
that's why things appear closer.
--
David Dyer-Bennet, <mailto:D d-b@dd-b.net>, <http://www.dd-b.net/dd-b/&gt;
RKBA: <http://noguns-nomoney.com/&gt; <http://www.dd-b.net/carry/&gt;
Pics: <http://dd-b.lighthunters.net/&gt; <http://www.dd-b.net/dd-b/SnapshotAlbum/&gt;
Dragaera/Steven Brust: <http://dragaera.info/&gt;
Anonymous
May 13, 2005 7:01:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

JD wrote:

> Hi,
> 1.Is it true to say that if I use a 50mm lens from a 35mm camera on a
> Digital SLR, I get the equivalent of a 75mm lens?

As long as you carefully use words like "equivalent" or "effective"
focal length then it's reasonably true.

The commonly used term is "crop factor", and people immediately ignore
the math and present the FL enlargement factor, such as 1.5X (Nikon D70,
Pentax *ist, Minolta 7D) or 1.6X for the 20D/10D, etc.

Depth of field, being print size related, and hence enlargement factor
related, also is different (shallower) than the full frame image
enlarged to the same degree would provide.


> 2. If the answer to question #1 it is yes, then is my subject getting closer
> (as if I was using a telephoto) *and* the view angle getting narrower or is
> it just the view angle getting narrower *without* the subject getting

A lens doesn't make anything closer or farther. It magnifies by some
amount. The effect of the crop factor is to have smaller angle of view,
hence objects further away appear larger in the viewfinder (and in the
image) on a cropped sensor camera.

Cheers,
Alan


--
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May 13, 2005 7:22:29 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

> The latter. The multiplier comes from the fact that the digital
> sensor is smaller than the full 35mm frame size. It's really a field
> of view crop rather than optical magnification. Picture shooting
> onto a 35mm negative, but then only being allowed to use the center
> area of the film rather than the entire frame.
>
> Best Regards,
> --
> Todd H.
> http://www.toddh.net/

Thanks Todd for your quick answer.
As a consequence of that you wrote, the subject occupies more space in the
viewfinder and therefore must seem closer...
Jean.
Anonymous
May 13, 2005 7:22:30 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"JD" <no.spam.jdon@wanadoo.fr> writes:

> > The latter. The multiplier comes from the fact that the digital
> > sensor is smaller than the full 35mm frame size. It's really a field
> > of view crop rather than optical magnification. Picture shooting
> > onto a 35mm negative, but then only being allowed to use the center
> > area of the film rather than the entire frame.
> >
> > Best Regards,
> > --
> > Todd H.
> > http://www.toddh.net/
>
> Thanks Todd for your quick answer.
> As a consequence of that you wrote, the subject occupies more space in the
> viewfinder and therefore must seem closer...

It does, but as folks are pretty prickly and correct to point out
often in this forum, the visual effect of field of view crop is
different than true magnification.

But, yeah, stuff seems bigger and closer than it would on a film
camera. :-)

Best Regards,
--
Todd H.
http://www.toddh.net/
May 13, 2005 8:19:42 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"Todd H." <t@toddh.net> wrote in message news:84k6m3fe05.fsf@ripco.com...
> "JD" <no.spam.jdon@wanadoo.fr> writes:
>
> > > The latter. The multiplier comes from the fact that the digital
> > > sensor is smaller than the full 35mm frame size. It's really a field
> > > of view crop rather than optical magnification. Picture shooting
> > > onto a 35mm negative, but then only being allowed to use the center
> > > area of the film rather than the entire frame.
> > >
> > > Best Regards,
> > > --
> > > Todd H.
> > > http://www.toddh.net/
> >
> > Thanks Todd for your quick answer.
> > As a consequence of that you wrote, the subject occupies more space in
the
> > viewfinder and therefore must seem closer...
>
> It does, but as folks are pretty prickly and correct to point out
> often in this forum, the visual effect of field of view crop is
> different than true magnification.
>
> But, yeah, stuff seems bigger and closer than it would on a film
> camera. :-)
>
> Best Regards,
> --
> Todd H.
> http://www.toddh.net/

Thats right, so the "perspective" is not the same as when using a 1.6x50mm
(=80mm) lens on a t 35mm camera. When I say perspective it is the way
objects appear in the depth of field. For example, at telephoto, there is an
effect of "compression" (eg a line of trees apear compressed when using a
longer lens or focal length). The crop factor does not add to this
compression, but rather you get a "cropped" image and still keep the same
perspective. I hope this fully clarifies the question.

Thanks
Musty.
Anonymous
May 13, 2005 8:19:43 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Musty wrote:

> Thats right, so the "perspective" is not the same as when using a 1.6x50mm
> (=80mm) lens on a t 35mm camera. When I say perspective it is the way
> objects appear in the depth of field. For example, at telephoto, there is an
> effect of "compression" (eg a line of trees apear compressed when using a
> longer lens or focal length). The crop factor does not add to this
> compression, but rather you get a "cropped" image and still keep the same
> perspective. I hope this fully clarifies the question.

No it muddies it up a great deal! ;-)

[ You understand it, but you need to keep things distict ].

Depth of field is depth of field. It's apparent effect is only related
to the print. So enlarging from a smaller sensor to a given print size
results in less DOF in the print.

Perspective, most simply stated, is a question of distance to the
subject regardless of lens, focal length, film/sensor size, etc.

Cheers,
Alan.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
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-- e-meil: Remove FreeLunch.
Anonymous
May 13, 2005 10:04:18 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Musty <musty@nospam.net> wrote:

> Thats right, so the "perspective" is not the same as when using a 1.6x50mm
> (=80mm) lens on a t 35mm camera. When I say perspective it is the way
> objects appear in the depth of field. For example, at telephoto, there is an
> effect of "compression" (eg a line of trees apear compressed when using a
> longer lens or focal length). The crop factor does not add to this
> compression, but rather you get a "cropped" image and still keep the same
> perspective. I hope this fully clarifies the question.

Neither focal length nor crop factor has any effect on perspective.

If you make the same shot with a 50mm lens on a DSLR with a 1.5 crop factor,
and a 75mm lens on a 35mm camera, using the same framing, the perspective
will be the same. The "compression" of depth you refer to has nothing to
do with the focal length of the lens in use.

--
Jeremy | jeremy@exit109.com
Anonymous
May 13, 2005 10:54:02 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On 13 May 2005 09:43:21 -0700, Siddhartha Jain <losttoy@gmail.com> wrote:
>
> Comparing 35mm vs sub-35mm lenses reminds me of what I was doing today,
> that is, checking all my lenses. In one hand, I held a Minolta 35-70mm
> and in the other I held a Pentax Super Takumar 50mm f/1.4. The Pentax
> M42 mount lens has a much narrower barrel than the Minolta or my Canon
> lenses including the 18-55mm EF-S lens. Now wasn't sub-35mm sensor
> technology supposed to deliver lighter and smaller lenses?

I'd compare primes to primes, not to zooms. Not that many EF-S
primes out there; I only know of one, the 60mm macro. I guess you'd
have to compare it against a macro lens, since the floating element
might add bulk and weight.

--
Ben Rosengart (212) 741-4400 x215
Sometimes it only makes sense to focus our attention on those
questions that are equal parts trivial and intriguing.
--Josh Micah Marshall
May 13, 2005 11:15:38 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"Alan Browne" <alan.browne@freelunchVideotron.ca> wrote in message
news:D 62t17$2si$1@inews.gazeta.pl...
> Musty wrote:
>
> > Thats right, so the "perspective" is not the same as when using a
1.6x50mm
> > (=80mm) lens on a t 35mm camera. When I say perspective it is the way
> > objects appear in the depth of field. For example, at telephoto, there
is an
> > effect of "compression" (eg a line of trees apear compressed when using
a
> > longer lens or focal length). The crop factor does not add to this
> > compression, but rather you get a "cropped" image and still keep the
same
> > perspective. I hope this fully clarifies the question.
>
> No it muddies it up a great deal! ;-)
>

I may have used the DOF thing incorrectly. Ok, I did use it incorrectly.
Sorry about that.

> [ You understand it, but you need to keep things distict ].
>
> Depth of field is depth of field. It's apparent effect is only related
> to the print. So enlarging from a smaller sensor to a given print size
> results in less DOF in the print.

I agree. The DOF I suppose just relates to the depth of objects in
"relatively" good focus (atleast good enough for a certain print medium for
the human eye)

>
> Perspective, most simply stated, is a question of distance to the
> subject regardless of lens, focal length, film/sensor size, etc.

Ok, so I also used perspective incorrectly. So my question is regard to
"compression" and "expansion". If this is not perspective, what is the term
use? (I am asking)

This (compression, expansion) is something definitely affected by the focal
length and is not affected by cropping (obviously). So a 300mm lens will
compress the "trees" or wine barrels or whatever more than a 200mm lens
regardless if the crop factor is 1.0x , 1.5x, 1.6x, 2x etc. Is that a fair
statement?

Musty.

>
> Cheers,
> Alan.
>
> --
> -- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
> -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
> -- [SI] gallery & rulz: http://www.pbase.com/shootin
> -- e-meil: Remove FreeLunch.
Anonymous
May 13, 2005 11:15:39 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Musty wrote:

> This (compression, expansion) is something definitely affected by the focal
> length and is not affected by cropping (obviously). So a 300mm lens will
> compress the "trees" or wine barrels or whatever more than a 200mm lens
> regardless if the crop factor is 1.0x , 1.5x, 1.6x, 2x etc. Is that a fair
> statement?

It's easier to simply think in terms of angle of view. Say you're
standing 15 feet from the side a car that's 15 feet long. The angle of
view for you to see the car front to back is about 55°

Now back up 100 feet. Now the angle of view is less than 10°.

That's perspective. And it has nothing to do with the chosen lens.

For a lens, such as a 20mm, the case above will result in the middle of
the car bulging toward you, and the ends of the car shrinking in the
image. Your eyes do this too! You just don't notice it as much.

If you stand at one position far enough off and take a photo of a line
of trees from just off of the angle of the tree line, the 'compression'
is the same for a 50mm as it is for a 300mm. But normally, we don't
crop a 50mm shot 6X, so we don't notice the effect as much.

Cheers,
Alan

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
Anonymous
May 13, 2005 11:24:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Musty <musty@nospam.net> wrote:

> This (compression, expansion) is something definitely affected by the focal
> length and is not affected by cropping (obviously). So a 300mm lens will
> compress the "trees" or wine barrels or whatever more than a 200mm lens
> regardless if the crop factor is 1.0x , 1.5x, 1.6x, 2x etc. Is that a fair
> statement?

No. The focal length has nothing to do with it; it is caused by the position
of the camera relative to the subject and nothing else.

If you take your 300mm shot of the trees, with the "compression" effect of
perspective; then, standing in the same place, switch to a 17mm lens and take
the shot again, then enlarge the second image and crop out the center portion
so that it matches the framing of the 300mm shot, the perspective (and the
"compression") will be absolutely identical. Focal length has nothing to do
with it; a telephoto lens is simply cropping out the center portion of the
picture, it's just doing it optically.

--
Jeremy | jeremy@exit109.com
Anonymous
May 14, 2005 1:21:05 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On Fri, 13 May 2005 16:48:26 -0400, Alan Browne
<alan.browne@freelunchVideotron.ca> wrote:

>Musty wrote:
>
>> This (compression, expansion) is something definitely affected by the focal
>> length and is not affected by cropping (obviously). So a 300mm lens will
>> compress the "trees" or wine barrels or whatever more than a 200mm lens
>> regardless if the crop factor is 1.0x , 1.5x, 1.6x, 2x etc. Is that a fair
>> statement?
>
>It's easier to simply think in terms of angle of view. Say you're
>standing 15 feet from the side a car that's 15 feet long. The angle of
>view for you to see the car front to back is about 55°
>
>Now back up 100 feet. Now the angle of view is less than 10°.
>
>That's perspective. And it has nothing to do with the chosen lens.
>
>For a lens, such as a 20mm, the case above will result in the middle of
>the car bulging toward you, and the ends of the car shrinking in the
>image. Your eyes do this too! You just don't notice it as much.
>
>If you stand at one position far enough off and take a photo of a line
>of trees from just off of the angle of the tree line, the 'compression'
>is the same for a 50mm as it is for a 300mm. But normally, we don't
>crop a 50mm shot 6X, so we don't notice the effect as much.

Ahh.. it's about time for the return of 'The Perspective Wars'...

What about barrel distortion?

;-)

...better still, ignore I said that.

Uh, shouldn't you have qualified your lenses as having to be
rectilinear?

....no, don't start...ignore me still...

....refrain...

--
Owamanga!
http://www.pbase.com/owamanga
Anonymous
May 14, 2005 2:11:26 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In article <1189vo5pgjeqj5f@corp.supernews.com>,
Jeremy Nixon <jeremy@exit109.com> wrote:
>Musty <musty@nospam.net> wrote:
>> This (compression, expansion) is something definitely affected by the focal
>> length and is not affected by cropping (obviously). So a 300mm lens will
>> compress the "trees" or wine barrels or whatever more than a 200mm lens
>> regardless if the crop factor is 1.0x , 1.5x, 1.6x, 2x etc. Is that a fair
>> statement?
>
>then enlarge the second image and crop out the center portion
>so that it matches the framing of the 300mm shot, the perspective (and the
>"compression") will be absolutely identical.

From this we can conclude that it is simply field-of-view.

There is however one catch, it is the field of view in the print (or other
kind of display) that you are watching that determines whether perspective
is compressed or expanded. If the print shows a smaller field of view than
what you can expect to see based on the size of the print and distance
from which you are watching the print, then the perspective appears
compressed.

On the other hand, if the print shows more, you get a wide-angle view.
As you get closer to a wide-angle print, the perspective may become more
'normal'.


--
That was it. Done. The faulty Monk was turned out into the desert where it
could believe what it liked, including the idea that it had been hard done
by. It was allowed to keep its horse, since horses were so cheap to make.
-- Douglas Adams in Dirk Gently's Holistic Detective Agency
May 14, 2005 4:19:03 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Jeremy Nixon wrote:

> Musty <musty@nospam.net> wrote:
>
>> This (compression, expansion) is something definitely affected by the
>> focal
>> length and is not affected by cropping (obviously). So a 300mm lens
>> will compress the "trees" or wine barrels or whatever more than a 200mm
>> lens regardless if the crop factor is 1.0x , 1.5x, 1.6x, 2x etc. Is that
>> a fair statement?
>
> No. The focal length has nothing to do with it; it is caused by the
> position of the camera relative to the subject and nothing else.
>
> If you take your 300mm shot of the trees, with the "compression" effect of
> perspective; then, standing in the same place, switch to a 17mm lens and
> take the shot again, then enlarge the second image and crop out the center
> portion so that it matches the framing of the 300mm shot, the perspective
> (and the
> "compression") will be absolutely identical.

And doesn't the viewing distance from the print also enter into if it seems
compressed perspective etc? Just asking as it seems like I read that
somewhere..

--

Stacey
Anonymous
May 14, 2005 8:23:16 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga wrote:

> Ahh.. it's about time for the return of 'The Perspective Wars'...
>
> What about barrel distortion?

Perspective is perspective regardless of other (non) qualities.

Besides, Musty clearly understands it, he's just not famillar with all
the distinctions and definitions.

So, no war. Just a treaty. Damn it.

Cheers,
Alan


--
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Anonymous
May 14, 2005 9:28:22 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Tony Polson wrote:

> The perspective of a shot is simply what it is, being defined solely
> by the camera's position relative to the subject, regardless of the
> focal length of the lens in use. It cannot be "compressed".
>
> You should buy a book on the basics of photography and learn what
> perspective means. Then you will be in no doubt.

So, perhaps, should you Tony. One of the most 'basic' photography
books, the National Geographic Photography Field Guide, has a paragraph
entitled, "Compressed Perspective" on page 63 and talks specifically
about the effect (appearance or illusion if you prefer) of telephoto lenses.

Cheers,
Alan.

--
-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm
-- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm
-- [SI] gallery & rulz: http://www.pbase.com/shootin
-- e-meil: Remove FreeLunch.
Anonymous
May 15, 2005 3:46:26 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

JD wrote:
>
> Hi,
> 1.Is it true to say that if I use a 50mm lens from a 35mm camera on a
> Digital SLR, I get the equivalent of a 75mm lens?
> 2. If the answer to question #1 it is yes, then is my subject getting closer
> (as if I was using a telephoto) *and* the view angle getting narrower or is
> it just the view angle getting narrower *without* the subject getting
> closer?
> Regards,
> Jean.

The image thrown by a given lens does not change with a change in
film/sensor size. All a smaller sensor does is record only the part of
the image that falls on the sensor, the rest of the image is lost. More
image is recorded on a larger sensor or film, but it is the same image.
All that happens is you get a wider field of view, whereas a small
sensor gives a narrower field of view.

The *effect* of a narrower field of view can be duplicated on a larger
sensor by changing to a longer lens, so (in your example) the field of
view of a 50mm lens on a dslr can be duplicated witha 75mm lens on a
35mm camera. Larger sensor, larger image, longer lens. It's all in
direct ratio.

Colin.
Anonymous
May 15, 2005 4:44:35 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <1189vo5pgjeqj5f@corp.supernews.com>,
Jeremy Nixon <jeremy@exit109.com> wrote:

>Focal length has nothing to do
>with it; a telephoto lens is simply cropping out the center portion of the
>picture, it's just doing it optically.

.... and they can't focus close enough to make someone's nose twice as
big as their ears.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
May 15, 2005 5:28:40 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <d65qhj$4nt$1@inews.gazeta.pl>,
Alan Browne <alan.browne@freelunchVideotron.ca> wrote:

>So, perhaps, should you Tony. One of the most 'basic' photography
>books, the National Geographic Photography Field Guide, has a paragraph
>entitled, "Compressed Perspective" on page 63 and talks specifically
>about the effect (appearance or illusion if you prefer) of telephoto lenses.

Well, that is true pragmatically, because you don't want to crop a 10mm
lens for the same effect, and lose most of the resolution of your
recording medium.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
May 15, 2005 1:17:08 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Alan Browne wrote:

> Tony Polson wrote:
>
>> The perspective of a shot is simply what it is, being defined solely
>> by the camera's position relative to the subject, regardless of the
>> focal length of the lens in use. It cannot be "compressed".
>>
>> You should buy a book on the basics of photography and learn what
>> perspective means. Then you will be in no doubt.
>
>
> So, perhaps, should you Tony. One of the most 'basic' photography
> books, the National Geographic Photography Field Guide, has a paragraph
> entitled, "Compressed Perspective" on page 63 and talks specifically
> about the effect (appearance or illusion if you prefer) of telephoto
> lenses.


I still can't wrap my head around the compression of perspective notion.
Let me think aloud here... Hmm so if there is a bird in the foreground
and a building beyond, they are both the same height at 70mm in the
frame... zooming in to 200mm I guess they are indeed the same height
still... now if you step back AND zoom to 200mm till the bird is the
same percent of the frame as it was at 50mm, then the building "grows"
taller than the bird. So there is such a thing as compressed perspective
and it is accomplished with a long lens but it requires more than just
zooming, it also requires walking back away from the foreground... that
makes sense.

What doesn't make sense is looking at a line of telephone poles. There
is an angle on the print of a picture which can be measured. That angle
ought not to change no matter what zoom you use... it is a straight
line! So how does the building grow bigger than the bird in the first
example if it is a straight line? Thinking of it in terms of cropping or
magnification, the closest two telephone poles should have the same
ratio between their heights as the last two telephone poles... the
"compressed perspective" exists in the wide view, you just have to crop
the picture to see it??? Or is that wrong and the ratio of height
between the first two and the last two poles different? It must be.
Things closer to the camera must show more distortion (greater percent
difference in height between two adjacent poles) but the zoomed/cropped
view loses sight of the closest telephone poles off the edge of the
frame so all you can fit in the frame is the further poles which are
less distorted.

Thanks for letting me muddle through that: There is more perspective
distortion in close objects, more perspective compression (equalization
actually) in distant objects. Telephoto lenses enlarge the less
distorted part that exists in a wide angle lens. The less distorted part
in a wide angle view is tiny in the middle so is not noticeable.


--
Paul Furman
http://www.edgehill.net/1
san francisco native plants
Anonymous
May 15, 2005 2:44:19 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"Musty" <musty@nospam.net> writes:
> This (compression, expansion) is something definitely affected by
> the focal length and is not affected by cropping (obviously).

I use a Canon Powershot G5 a lot. It has a zoom with a focal length
from 7 mm to 28 mm. On this camera, because of its small sensor,
28 mm is /tele/. It results in the same "perspective" (i.e. appearent
"compression" effect) that a 140 mm lens would give on a camera using
135 film if used it to photograph the same subject from the same
position.

The "wide-angle expansion" that you seem to think would be the result
when shooting with a 28 mm lens simply does not happen. If I were to
show you two 8x10 prints of (say) an image of a row of telegraph poles
vanishing into the distance from the shots taken with the film camera
with f=140 mm, and the Canon G5 with f=28 mm - you would not be able
to tell the difference.

> So a 300mm lens will compress the "trees" or wine barrels or
> whatever more than a 200mm lens regardless if the crop factor is
> 1.0x , 1.5x, 1.6x, 2x etc. Is that a fair statement?

Sure. As long as you make sure that you are comparing apples with
apples (i.e. compare focal lenghts without changing the size of
the imager).

The mistake a lot of people make is that they believe that the
"effect" they get from using a lens of a particular focal length
does not change if they change the size of the imager. It does.
This is very obvious when you look at the "tele" effect you get
when using a focal length of 28 mm on a digital compact camera.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
------------------------------------------------------------------------
Kodak DCS460, Canon Powershot G5, Olympus 2020Z
------------------------------------------------------------------------
Anonymous
May 15, 2005 6:50:39 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

To make it simpler do the exercise.

Shoot a row of trees while standing 15 feet off of the line of trees
with a 50mm lens. Then back off on a line parallel to the tree line
(remain 15 feet from the tree line) far enough to fit the same trees
into the view of a 200 or 300mm lens. The compressed look will be
evident enough. Shoot that same second shot with the 50mm, and crop it
down to the same view as the 200 or 300 ... and the perspective will be
shown to be identical ... and the compresion look too.

On small aperture shots of subejcts far enough away the distance between
objects along that axis can be lost in the compression. Sometimes with
confusing results.

Cheers,
Alan


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Anonymous
May 16, 2005 1:53:01 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

In message <Ga6dneR_lLqY6xrfRVn-uQ@speakeasy.net>,
Paul Furman <paul-@-edgehill.net> wrote:

>the closest two telephone poles should have the same
>ratio between their heights as the last two telephone poles...

They shouldn't, and they don't. The angle that the poles subtend is
inversely proportional to their distance from your vantage point: 1/2,
1/3, 1/4, 1/5, 1/6, 1/7, 1/8, etc, as they get further away from you and
are equally spaced. 1/2 / 1/3 = 3/2 = 1.5. 1/7 / 1/8 = 8/7 = 1.14
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
May 16, 2005 1:53:02 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

JPS@no.komm wrote:

> In message <Ga6dneR_lLqY6xrfRVn-uQ@speakeasy.net>,
> Paul Furman <paul-@-edgehill.net> wrote:
>
>
>>the closest two telephone poles should have the same
>>ratio between their heights as the last two telephone poles...
>
>
> They shouldn't, and they don't. The angle that the poles subtend is
> inversely proportional to their distance from your vantage point: 1/2,
> 1/3, 1/4, 1/5, 1/6, 1/7, 1/8, etc, as they get further away from you and
> are equally spaced. 1/2 / 1/3 = 3/2 = 1.5. 1/7 / 1/8 = 8/7 = 1.14


Hmmm... yes...

OK, here's a way to put it that makes intuitive sense in a visual rather
than mathematical way:

Perspective shrinks out to a "vanishing" point and an infinite line of
poles would never actually vanish from sight, just get smaller more and
more gradually. The first few get smaller quickly (lots of distortion).
Far away, there isn't much room to shrink so there is much less distortion.

If you zoomed in to a million miles away on this line of poles, they
would all look about the same height. This is actually less distorted so
it should look normal but our eyes are accustomed to seeing things fade
in perspective at about 50mm (I assume that's where 50mm "normal" comes
from). So if the lens is wider or longer than 50mm, things look
abnormal, out of kilter, unnatural.

Applying that again to the 1.5 crop of DSLRs would it be incorrect to
say that a 35mm lens is a "normal" lens because it would really be more
distorted? No because the field of view is less... so printed at the
same size, the crop factor IS EXACTLY THE SAME AS ZOOMING. The size of
the sensor is really irrelevant because there can be a variety of
different pixel densities.

From that I conclude that people are correct when they say "my 200mm
lens is really a 350mm lens on the digital" well, not technically
correct with that wording but the intent is absolutely correct.

So... is the DOF actually different? If you print at the same size? If
so, that's the only difference. I don't think it is different. I think
cropping is exactly the same as zooming in all respects as long as you
print at the same size and the lens/sensor is sensitive enough to pick
up the detail.

Now for the bonus question. Does stepping away from a print change the
zoom/crop factor? Does it make the distortion less? More? Not really
because we think of the angle of view as defining the image in terms of
perspective distortion & we know it's a picture. If we thought it was a
window, that might work. Stepping closer to a print decreases distortion
only if it's big enough that it goes outside out field of view.

However, stepping away from a print does increase the DOF because we
can't focus well enough at a distance to distinguish the blur, the whole
picture looks sharper.


--
Paul Furman
http://www.edgehill.net/1
san francisco native plants
Anonymous
May 16, 2005 1:25:33 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

"Musty" <musty@nospam.net> writes:
> "Alan Browne" <alan.browne@freelunchVideotron.ca> wrote:

>> Perspective, most simply stated, is a question of distance to the
>> subject regardless of lens, focal length, film/sensor size, etc.

> Ok, so I also used perspective incorrectly. So my question is regard
> to "compression" and "expansion". If this is not perspective, what
> is the term use? (I am asking)

The "compression" look associated with telephoto lenses and
"expansion" associated with wide-angle lenses is often (and
IMHO) correctly referred to as "perspective".

> This (compression, expansion) is something definitely affected by
> the focal length and is not affected by cropping (obviously).

Take a look at the two photographs on this page. It shows the same
scene shot with a 135 mm lens and a 28 mm lens. The 28 mm lens
image is cropped so that it exactly matches the FOV of the 135 mm
lens: http://folk.uio.no/gisle/photo/crop.html#per .

As you can clearly see, the perspective (compression look) is the
same, so it is /not/ in any way affected by the focal length used.
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
------------------------------------------------------------------------
Kodak DCS460, Canon Powershot G5, Olympus 2020Z
------------------------------------------------------------------------
Anonymous
May 16, 2005 3:11:50 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Gisle Hannemyr wrote:

> As you can clearly see, the perspective (compression look) is the
> same, so it is /not/ in any way affected by the focal length used.

Ahem. The way somebody would normally use each of those lenses (that is
to say, not crop small sections of wider angle shots) is why longer FL's
usually show the compressed effect in the final image and the wider
angle don't. You usually photography with a FL appropriate to the final
print, IOW.


--
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Anonymous
May 17, 2005 1:08:32 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Alan Browne <alan.browne@freelunchVideotron.ca> wrote:

> So, perhaps, should you Tony. One of the most 'basic' photography
> books, the National Geographic Photography Field Guide, has a
> paragraph entitled, "Compressed Perspective" on page 63 and talks
> specifically about the effect (appearance or illusion if you prefer)
> of telephoto lenses.
>
>

Then they're wrong or they're aware that they're writing for people who
could never comprehend the reality of the situation.
Anonymous
May 17, 2005 1:08:33 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Bubbabob wrote:
> Alan Browne <alan.browne@freelunchVideotron.ca> wrote:
>
>
>>So, perhaps, should you Tony. One of the most 'basic' photography
>>books, the National Geographic Photography Field Guide, has a
>>paragraph entitled, "Compressed Perspective" on page 63 and talks
>>specifically about the effect (appearance or illusion if you prefer)
>>of telephoto lenses.
>>
>>
>
>
> Then they're wrong or they're aware that they're writing for people who
> could never comprehend the reality of the situation.

The term 'compression' is an awkward one, but what better to describe a
presentation of a scene that looks very flat when we know there is more
than the presented depth?

It is all in the eye of the beholder. But the print he is holding in
his hand is not a scene as he would normally take it in with his eyes.

1) We "see" a scene that is fairly large, about 40 or 50° wide. So a
print (or screenshot) that shows a narrow telephoto view is missing the
information that we usually have to judge the scene.

2) We focus on what we are looking at. We can't even control that.
Whereas a telephoto shot, esp. one with deep DOF is presented as we
never perceive it with out eyes. The print is always in focus, even the
out of focus parts.

Oddly enough, an hour ago I was watching a NOVA DVD (Elegant Universe)
which opened with a television commercial with a car travelling a very
long and stragiht piece of highway. The powerline poles on the left and
near the POV, looked 'normal'; the the phone polls in the distance
looked packed closer together as persepctive normally shows.

In my mind I cropped the distant poles and imageined the image blown
up... indeed a compression effect. IOW, had a long lens been used from
the same POV, those poles in the distance would have looked to be
compressed.

In the program that followed, the narrator walked, talking, towards the
camera down a busy city sidewalk, isolated by the narrow FOV. All the
'business' and depth of the scene was compressed by the narrow FOV.
(eg: street signs loomed large in the FG but looker close to him in the
presented image .. the sense of depth was lost).

An example from photozone...
http://www.photozone.de/4Technique/compose/focal.htm

http://www.photozone.de/4Technique/compose/compress.htm

So no, they're not wrong. At worst, the word compression is just
awkward. In the context of perspective and long lenses it is the term
that usually comes up. If you have better one word description, let's
hear it.

Cheers,
Alan.

--
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Anonymous
May 17, 2005 2:28:48 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Bubbabob <rnorton@_remove_this_thuntek.net> wrote:

>Alan Browne <alan.browne@freelunchVideotron.ca> wrote:
>
>> So, perhaps, should you Tony. One of the most 'basic' photography
>> books, the National Geographic Photography Field Guide, has a
>> paragraph entitled, "Compressed Perspective" on page 63 and talks
>> specifically about the effect (appearance or illusion if you prefer)
>> of telephoto lenses.
>>
>>
>
>Then they're wrong or they're aware that they're writing for people who
>could never comprehend the reality of the situation.


They are of course absolutely wrong, but most people who buy the NG
Field Guide wouldn't ever notice.

Still, on balance, if it encourages people to take up photography, or
engage in it on a more serious basis, the NG Field Guide can only be a
good thing. Hopefully, people who begin to take a more serious
interest in photography will soon realise that this unfortunate basic
error was just one of several in the Guide.

We should therefore be wary of quoting from the NG Field Guide as
though it in any way resembled a respected work of reference,
especially when it is so patently wrong on such a fundamental issue.
Anonymous
May 17, 2005 2:28:49 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Tony Polson wrote:

> They are of course absolutely wrong, but most people who buy the NG
> Field Guide wouldn't ever notice.

REF: http://tinyurl.com/c47ls
*************************************************************
FROM: Tony Polson Jun 14 2001, 7:36 am

Hi Greg,

If you want to learn how today's National Geographic shooters work, try
reading the National Geographic Field Guide by Robert Caputo and Peter
Burian. It makes interesting reading.

Best regards,

--
Tony Polson
**************************************************************
Anonymous
May 17, 2005 2:28:49 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Tony Polson wrote:

> They are of course absolutely wrong, but most people who buy the NG
> Field Guide wouldn't ever notice.

The specific phrase used in the book is:

"Telephoto lenses make objects at various distances appear closer
together than the naked eye perceives."

Like most such references, they are referring to the look of the image.
They do not say that the scene *is* compressed, they say that the
scene "appears" compressed. Compression being in the depth of the scene.

What is "absolutely wrong" about that?

Please explain it in definite terms, Tony.

> Still, on balance, if it encourages people to take up photography, or
> engage in it on a more serious basis, the NG Field Guide can only be a
> good thing. Hopefully, people who begin to take a more serious
> interest in photography will soon realise that this unfortunate basic
> error was just one of several in the Guide.

Please be specic with references and state your rebuttal, in detail.

> We should therefore be wary of quoting from the NG Field Guide as
> though it in any way resembled a respected work of reference,
> especially when it is so patently wrong on such a fundamental issue.

Indeed? Have you changed your tune, then?

"If you want to learn how today's National Geographic shooters work, try
reading the National Geographic Field Guide by Robert Caputo and Peter
Burian. It makes interesting reading." -- June 2001 --Tony Polson
Ref: http://tinyurl.com/c47ls

"Anyone who has the slightest doubt about Peter's ability as a writer on
photography should read the National Geographic Field Guide he
co-authored. It's *excellent*." -- Nov 2000 --Tony Polson
Ref: http://tinyurl.com/7dd34

"National Geographic Photography Field Guide (Burian/Caputo).
Excellent!" --Tony Polson --Dec 2000
Ref: http://tinyurl.com/awuq6

"A Happy New Year and welcome back to the newsgroup. Since Christmas I
have been enjoying reading the National Geographic Field Guide; it's one
of the most enjoyable books about photography I've ever read and it is
without doubt the most readable." --Jan 2001 --Tony Polson
Ref: http://tinyurl.com/7g4cy

The 'must buy' book is the National Geographic Field Guide to
Photography by Peter K Burian and Robert Caputo. It's available in
paperback for a mere £11.99 from stock at Amazon:
-- Nov 2000 -- Tony Polson
Ref: http://tinyurl.com/a2cpn

Cheers,
Alan.

--
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Anonymous
May 17, 2005 8:50:20 AM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Alan Browne <alan.browne@freelunchVideotron.ca> writes:
> Gisle Hannemyr wrote:

>> As you can clearly see, the perspective (compression look) is the
>> same, so it is /not/ in any way affected by the focal length used.

> Ahem. The way somebody would normally use each of those lenses
> (that is to say, not crop small sections of wider angle shots) is
> why longer FL's usually show the compressed effect in the final
> image and the wider angle don't. You usually photography with a FL
> appropriate to the final print, IOW.

And that is what I did.

You didn't even bother look at the page before typing in your
comment, did you?
--
- gisle hannemyr [ gisle{at}hannemyr.no - http://folk.uio.no/gisle/ ]
------------------------------------------------------------------------
Kodak DCS460, Canon Powershot G5, Olympus 2020Z
------------------------------------------------------------------------
Anonymous
May 17, 2005 12:53:51 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Gisle Hannemyr wrote:

> Alan Browne <alan.browne@freelunchVideotron.ca> writes:
>
>>Gisle Hannemyr wrote:
>
>
>
>>>As you can clearly see, the perspective (compression look) is the
>>>same, so it is /not/ in any way affected by the focal length used.
>
>
>
>>Ahem. The way somebody would normally use each of those lenses
>>(that is to say, not crop small sections of wider angle shots) is
>>why longer FL's usually show the compressed effect in the final
>>image and the wider angle don't. You usually photography with a FL
>>appropriate to the final print, IOW.
>
>
> And that is what I did.
>
> You didn't even bother look at the page before typing in your
> comment, did you?

Yes I did. The point still required clarification.

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Anonymous
May 17, 2005 6:06:23 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On Mon, 16 May 2005 20:45:01 -0400, Alan Browne
<alan.browne@freelunchVideotron.ca> wrote:

>Bubbabob wrote:
>> Alan Browne <alan.browne@freelunchVideotron.ca> wrote:
>>
>>
>>>So, perhaps, should you Tony. One of the most 'basic' photography
>>>books, the National Geographic Photography Field Guide, has a
>>>paragraph entitled, "Compressed Perspective" on page 63 and talks
>>>specifically about the effect (appearance or illusion if you prefer)
>>>of telephoto lenses.
>>
>> Then they're wrong or they're aware that they're writing for people who
>> could never comprehend the reality of the situation.
>
>The term 'compression' is an awkward one, but what better to describe a
>presentation of a scene that looks very flat when we know there is more
>than the presented depth?

Alan, I believe you are wasting your time. This type of argument was
used in the first perspective wars, and NG members like Tony patently
refuse to see any wider definition of the word/concept than the
extremely limited one defined as the photographers location in
relation to the subject.

Bitch-slapping Tony (in that other post) probably doesn't help much
either. :-) Funny though.

>It is all in the eye of the beholder.

Indeed.

Some dead guy wrote a book called 'The Camera', in which he states on
pages 97 & 106 "True perspective depends only on upon the
camera-to-subject distance." but he does acknowledge the terms
"wide-angle perspective" and "telephoto perspective", albeit as
"imprecise terms". He was of course, Ansel Adams.

My problem with his oversimplification is this: Can a tilt-lens affect
perspective? - If it can, how does it do that without significantly
changing the 'camera-to-subject' distance that Adams insists defines
perspective?

If a tilted film plane can affect perspective then so can a crop, a
frame, a telephoto lens and even an aperture setting - through optical
illusion maybe, but the effect is loosely termed 'perspective'.

I picked up a copy of a UK mag last week (Total Digital Photography),
which had a cool article on making a lilliputian train scene - from an
original photo of a life-sized British Rail train at a station, using
photoshop to introduce a graduated lens blur to the foreground and
background, the train remained in focus on a horizontal line in the
center of the image. So, now because of the tight DOF, it looks like a
toy train. The viewer believes they are a few inches away from the
train, instead of 150ft away where the original picture was taken -
so, if I can change the appearance of the camera-to-object distance,
have I not also altered perspective? - It fit's within Ansel's
definition.

To demonstrate this affect (my description is poor) I followed the
tutorial on the cover CD and came up with this:
http://www.pbase.com/owamanga/image/43502987

Due to copyright issues, that may not stay up for long...

--
Owamanga!
http://www.pbase.com/owamanga
Anonymous
May 17, 2005 6:06:24 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga wrote:

> On Mon, 16 May 2005 20:45:01 -0400, Alan Browne
> <alan.browne@freelunchVideotron.ca> wrote:
>
>
>>Bubbabob wrote:
>>
>>>Alan Browne <alan.browne@freelunchVideotron.ca> wrote:
>>>
>>>
>>>
>>>>So, perhaps, should you Tony. One of the most 'basic' photography
>>>>books, the National Geographic Photography Field Guide, has a
>>>>paragraph entitled, "Compressed Perspective" on page 63 and talks
>>>>specifically about the effect (appearance or illusion if you prefer)
>>>>of telephoto lenses.
>>>
>>>Then they're wrong or they're aware that they're writing for people who
>>>could never comprehend the reality of the situation.
>>
>>The term 'compression' is an awkward one, but what better to describe a
>>presentation of a scene that looks very flat when we know there is more
>>than the presented depth?
>
>
> Alan, I believe you are wasting your time. This type of argument was
> used in the first perspective wars, and NG members like Tony patently
> refuse to see any wider definition of the word/concept than the
> extremely limited one defined as the photographers location in
> relation to the subject.

The notion that perspective is isolated to the POV is solid and
acceptable. What I believe people are 'mixing up' is what the term
'compression' means.

In the sense of one object behind another, compression does _not_ mean
their vertical or horizontal presentation. In that sense, proportions
are maintained geometrically (aside from lens distortion, of course).

It _does_ mean that in terms of depth perception there is a flattening
of the image referred to by many as compression.

>>It is all in the eye of the beholder.

> Indeed.
>
> Some dead guy wrote a book called 'The Camera', in which he states on
> pages 97 & 106 "True perspective depends only on upon the
> camera-to-subject distance." but he does acknowledge the terms
> "wide-angle perspective" and "telephoto perspective", albeit as
> "imprecise terms". He was of course, Ansel Adams.
>
> My problem with his oversimplification is this: Can a tilt-lens affect
> perspective? - If it can, how does it do that without significantly
> changing the 'camera-to-subject' distance that Adams insists defines
> perspective?

I'm no expert on tilt-shift lenses, far from it. But my take is that a
tilt shift lens does not change perspective, it changes the projection
onto the negative. I know that sounds like heads of pins and angels.

To me, architectural photos are not perspective correct, they are
architecure presentation correct. Your eye sees the way a 'normal' lens
sees but, as it always has the same FOV, and human vision is very
subjective, you do not notice it in most situations. Take a card and
cut a rectangle into it and view a tall building through it, and voila,
you will see as any FL lens (from about 50mm up) sees by simply moving
the card in and out to crop the image.

<snipped>
> toy train. The viewer believes they are a few inches away from the
> train, instead of 150ft away where the original picture was taken -
> so, if I can change the appearance of the camera-to-object distance,
> have I not also altered perspective? - It fit's within Ansel's
> definition.
>
> To demonstrate this affect (my description is poor) I followed the
> tutorial on the cover CD and came up with this:
> http://www.pbase.com/owamanga/image/43502987

I'm sorry, but all I see is an image that has been blurred fore and aft
to isolate the train. It does not give me the sense that I'm close up
to a tiny train model.

Cheers,
Alan


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Anonymous
May 17, 2005 6:06:24 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga wrote:
> On Mon, 16 May 2005 20:45:01 -0400, Alan Browne
> <alan.browne@freelunchVideotron.ca> wrote:
>
>> Bubbabob wrote:
>>> Alan Browne <alan.browne@freelunchVideotron.ca> wrote:
>>>
>>>
>>>> So, perhaps, should you Tony. One of the most 'basic'
>>>> photography
>>>> books, the National Geographic Photography Field Guide, has a
>>>> paragraph entitled, "Compressed Perspective" on page 63 and talks
>>>> specifically about the effect (appearance or illusion if you
>>>> prefer) of telephoto lenses.
>>>
>>> Then they're wrong or they're aware that they're writing for
>>> people
>>> who could never comprehend the reality of the situation.
>>
>> The term 'compression' is an awkward one, but what better to
>> describe a presentation of a scene that looks very flat when we
>> know
>> there is more than the presented depth?
>
> Alan, I believe you are wasting your time. This type of argument was
> used in the first perspective wars, and NG members like Tony
> patently
> refuse to see any wider definition of the word/concept than the
> extremely limited one defined as the photographers location in
> relation to the subject.
>
> Bitch-slapping Tony (in that other post) probably doesn't help much
> either. :-) Funny though.
>
>> It is all in the eye of the beholder.
>
> Indeed.
>
> Some dead guy wrote a book called 'The Camera', in which he states
> on
> pages 97 & 106 "True perspective depends only on upon the
> camera-to-subject distance." but he does acknowledge the terms
> "wide-angle perspective" and "telephoto perspective", albeit as
> "imprecise terms". He was of course, Ansel Adams.
>
> My problem with his oversimplification is this: Can a tilt-lens
> affect
> perspective? - If it can, how does it do that without significantly
> changing the 'camera-to-subject' distance that Adams insists defines
> perspective?
>
> If a tilted film plane can affect perspective then so can a crop, a
> frame, a telephoto lens and even an aperture setting - through
> optical
> illusion maybe, but the effect is loosely termed 'perspective'.
>
> I picked up a copy of a UK mag last week (Total Digital
> Photography),
> which had a cool article on making a lilliputian train scene - from
> an
> original photo of a life-sized British Rail train at a station,
> using
> photoshop to introduce a graduated lens blur to the foreground and
> background, the train remained in focus on a horizontal line in the
> center of the image. So, now because of the tight DOF, it looks like
> a
> toy train. The viewer believes they are a few inches away from the
> train, instead of 150ft away where the original picture was taken -
> so, if I can change the appearance of the camera-to-object distance,
> have I not also altered perspective? - It fit's within Ansel's
> definition.
>
> To demonstrate this affect (my description is poor) I followed the
> tutorial on the cover CD and came up with this:
> http://www.pbase.com/owamanga/image/43502987
>
> Due to copyright issues, that may not stay up for long...

To my eye, untrained and rheumy as it is, your work looks like a
selectively blurred photograph. If I hadn't been forewarned, or not
had the comparison photo for, uh, comparison, I think I'd have
thought: "Hm. Wonder what that is supposed to represent".

--
Frank S

"Verbing wierds language."
-Calvin
Anonymous
May 17, 2005 7:34:57 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On Tue, 17 May 2005 07:48:57 -0700, "Frank ess" <frank@fshe2fs.com>
wrote:

>Owamanga wrote:
>
>> To demonstrate this affect (my description is poor) I followed the
>> tutorial on the cover CD and came up with this:
>> http://www.pbase.com/owamanga/image/43502987
>>
>> Due to copyright issues, that may not stay up for long...
>
>To my eye, untrained and rheumy as it is, your work looks like a
>selectively blurred photograph. If I hadn't been forewarned, or not
>had the comparison photo for, uh, comparison, I think I'd have
>thought: "Hm. Wonder what that is supposed to represent".

I don't actually have the mag with me, it looked better in print - I
have the tutorial CD, and followed the video on that. Selective
blurring is of course what has been done. I admit, my attempt doesn't
reflect what I recall in the mag too well. Oh well, I tried.

It's just an example... there is probably some... er.. skill involved
or something....

--
Owamanga!
http://www.pbase.com/owamanga
Anonymous
May 17, 2005 7:34:58 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga wrote:

> I don't actually have the mag with me, it looked better in print - I
> have the tutorial CD, and followed the video on that. Selective
> blurring is of course what has been done. I admit, my attempt doesn't
> reflect what I recall in the mag too well. Oh well, I tried.

Appropriately (or oddly) enough (your pick), I believe the problem is
simply that the blurring is not in the correct, natural distribution
(progression) that a lens would create from that downward looking angle.
Hence it looks artificial in that sense. Our visual BS detector goes off.

To me it recalls one of the early SI shots
http://www.pbase.com/shootin/image/22166132 that had an unnatural
out-of-focus area. The photographer (one of the better SI
contributors), was drawing attention to aspects of the child's
dissability (boundary). Gary was roundly criticized for this rule
breaking, including by me [ a) rules, b) didn't need it in the context
of the SI mandate ] Beyond that, most everyone commented that it simply
"didn't look right at all".

Cheers,
Alan.


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Anonymous
May 17, 2005 7:34:59 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Alan Browne wrote:

> Owamanga wrote:
>
>> I don't actually have the mag with me, it looked better in print - I
>> have the tutorial CD, and followed the video on that. Selective
>> blurring is of course what has been done. I admit, my attempt doesn't
>> reflect what I recall in the mag too well. Oh well, I tried.
>
>
> Appropriately (or oddly) enough (your pick), I believe the problem is
> simply that the blurring is not in the correct, natural distribution
> (progression) that a lens would create from that downward looking angle.
> Hence it looks artificial in that sense. Our visual BS detector goes off.

In addition to that, scenes are 3D, but photoshop work is 2D. So at a
down looking angle, there will be vertical objects that are OOF at their
base, but in-focus higher up as they cross into the DOF zone. This is
lost at a fine level in the image. Even the pole on the right, just the
other side of the train, should perhaps be in focus near its top. Our
ingrained visual processor just says 'error' without saying why...

This image is pretty wide angle as well, looking near vertical at the
bottom, and looking near horizontal at the top of the image. This makes
it even harder, I suppose, to effect the DOF effect properly.

Cheers,
Alan.

--
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Anonymous
May 17, 2005 7:47:53 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On Tue, 17 May 2005 10:40:39 -0400, Alan Browne
<alan.browne@freelunchVideotron.ca> wrote:

>Owamanga wrote:
>
>> On Mon, 16 May 2005 20:45:01 -0400, Alan Browne
>> <alan.browne@freelunchVideotron.ca> wrote:
>>
>>
>>>Bubbabob wrote:
>>>
>>>>Alan Browne <alan.browne@freelunchVideotron.ca> wrote:
>>>>
>>>>
>>>>
>>>>>So, perhaps, should you Tony. One of the most 'basic' photography
>>>>>books, the National Geographic Photography Field Guide, has a
>>>>>paragraph entitled, "Compressed Perspective" on page 63 and talks
>>>>>specifically about the effect (appearance or illusion if you prefer)
>>>>>of telephoto lenses.
>>>>
>>>>Then they're wrong or they're aware that they're writing for people who
>>>>could never comprehend the reality of the situation.
>>>
>>>The term 'compression' is an awkward one, but what better to describe a
>>>presentation of a scene that looks very flat when we know there is more
>>>than the presented depth?
>>
>>
>> Alan, I believe you are wasting your time. This type of argument was
>> used in the first perspective wars, and NG members like Tony patently
>> refuse to see any wider definition of the word/concept than the
>> extremely limited one defined as the photographers location in
>> relation to the subject.
>
>The notion that perspective is isolated to the POV is solid and
>acceptable. What I believe people are 'mixing up' is what the term
>'compression' means.

I guess where I'm coming from is this: Any rider/subclassification on
the word perspective, including 'compression' falls affects the
definition of perspective for that instance. 'Compressed perspective'

>In the sense of one object behind another, compression does _not_ mean
>their vertical or horizontal presentation. In that sense, proportions
>are maintained geometrically (aside from lens distortion, of course).
>
>It _does_ mean that in terms of depth perception there is a flattening
>of the image referred to by many as compression.

...so the viewer is under the (false) impression that two objects are
closer together than they actually are...right?

><snipped>
>> toy train. The viewer believes they are a few inches away from the
>> train, instead of 150ft away where the original picture was taken -
>> so, if I can change the appearance of the camera-to-object distance,
>> have I not also altered perspective? - It fit's within Ansel's
>> definition.
>>
>> To demonstrate this affect (my description is poor) I followed the
>> tutorial on the cover CD and came up with this:
>> http://www.pbase.com/owamanga/image/43502987
>
>I'm sorry, but all I see is an image that has been blurred fore and aft
>to isolate the train. It does not give me the sense that I'm close up
>to a tiny train model.

I guess I screwed it up... Once I get the mag again, I'll have another
go. It looked good more convincing in the mag.

--
Owamanga!
http://www.pbase.com/owamanga
Anonymous
May 17, 2005 7:47:54 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga wrote:

> ..so the viewer is under the (false) impression that two objects are
> closer together than they actually are...right?

Yes, and/or simply sees that it doesn't look as things normally look.

> I guess I screwed it up... Once I get the mag again, I'll have another
> go. It looked good more convincing in the mag.

See my other reply.

Cheers,
Alan
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Anonymous
May 17, 2005 10:43:29 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On Tue, 17 May 2005 13:16:59 -0400, Alan Browne
<alan.browne@freelunchVideotron.ca> wrote:

>Owamanga wrote:
>
>> I don't actually have the mag with me, it looked better in print - I
>> have the tutorial CD, and followed the video on that. Selective
>> blurring is of course what has been done. I admit, my attempt doesn't
>> reflect what I recall in the mag too well. Oh well, I tried.
>
>Appropriately (or oddly) enough (your pick), I believe the problem is
>simply that the blurring is not in the correct, natural distribution
>(progression) that a lens would create from that downward looking angle.
> Hence it looks artificial in that sense. Our visual BS detector goes off.

There was one thing I wasn't sure was correct in the tutorial - an
alpha channel was added, and then a reflected gradient (equal top and
bottom) was used to define the level of blurring, with a shift-lock on
the direction to make it exactly horizontal.

Horizontal I could understand, because the focal plane intersects the
scene at the horizontal, but equal back to front? Your tests on lenses
demonstrated that more of the COC lies behind the focal point than in
front. An equally matched gradient doesn't reflect that fact.

>To me it recalls one of the early SI shots
>http://www.pbase.com/shootin/image/22166132 that had an unnatural
>out-of-focus area. The photographer (one of the better SI
>contributors), was drawing attention to aspects of the child's
>dissability (boundary). Gary was roundly criticized for this rule
>breaking, including by me [ a) rules, b) didn't need it in the context
>of the SI mandate ] Beyond that, most everyone commented that it simply
>"didn't look right at all".

Photoshop... or perhaps one of those weird lenses that give you two
COC's at different distances...

<g>

That's a spooky image at a lot of levels.

--
Owamanga!
http://www.pbase.com/owamanga
Anonymous
May 17, 2005 10:43:30 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga wrote:

> There was one thing I wasn't sure was correct in the tutorial - an
> alpha channel was added, and then a reflected gradient (equal top and
> bottom) was used to define the level of blurring, with a shift-lock on
> the direction to make it exactly horizontal.
>
> Horizontal I could understand, because the focal plane intersects the
> scene at the horizontal, but equal back to front? Your tests on lenses
> demonstrated that more of the COC lies behind the focal point than in
> front. An equally matched gradient doesn't reflect that fact.

Yes, plus as I state in my addendum post, the downward angle really
screws up the 2D photoshop against focus plane and DOF field in a 3D
world...

The COC fore-aft asymetry depends on distance from the lens, focal
length, etc. as was discussed a month or so ago (and clearing me up on
an erroneous notion...)

> That's a spooky image at a lot of levels.

A lot of impact. Metaphorical 'boundary' and one of the stronger images
in that SI round.

Cheers,
Alan


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Anonymous
May 17, 2005 10:45:29 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

On Tue, 17 May 2005 13:33:30 -0400, Alan Browne
<alan.browne@freelunchVideotron.ca> wrote:

>Alan Browne wrote:
>
>> Owamanga wrote:
>>
>>> I don't actually have the mag with me, it looked better in print - I
>>> have the tutorial CD, and followed the video on that. Selective
>>> blurring is of course what has been done. I admit, my attempt doesn't
>>> reflect what I recall in the mag too well. Oh well, I tried.
>>
>>
>> Appropriately (or oddly) enough (your pick), I believe the problem is
>> simply that the blurring is not in the correct, natural distribution
>> (progression) that a lens would create from that downward looking angle.
>> Hence it looks artificial in that sense. Our visual BS detector goes off.
>
>In addition to that, scenes are 3D, but photoshop work is 2D. So at a
>down looking angle, there will be vertical objects that are OOF at their
>base, but in-focus higher up as they cross into the DOF zone. This is
>lost at a fine level in the image. Even the pole on the right, just the
>other side of the train, should perhaps be in focus near its top. Our
>ingrained visual processor just says 'error' without saying why...
>
>This image is pretty wide angle as well, looking near vertical at the
>bottom, and looking near horizontal at the top of the image. This makes
>it even harder, I suppose, to effect the DOF effect properly.

Good points, but in the nature of a rapid magazine tutorial, they
skipped all the steps where they rubberbanded all the different
objects based on height....

Even if they hadn't, for what I was doing, I certainly would have.

<g>

--
Owamanga!
http://www.pbase.com/owamanga
Anonymous
May 17, 2005 10:45:30 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga wrote:

> On Tue, 17 May 2005 13:33:30 -0400, Alan Browne
> <alan.browne@freelunchVideotron.ca> wrote:
>
>
>>Alan Browne wrote:
>>
>>
>>>Owamanga wrote:
>>>
>>>
>>>>I don't actually have the mag with me, it looked better in print - I
>>>>have the tutorial CD, and followed the video on that. Selective
>>>>blurring is of course what has been done. I admit, my attempt doesn't
>>>>reflect what I recall in the mag too well. Oh well, I tried.
>>>
>>>
>>>Appropriately (or oddly) enough (your pick), I believe the problem is
>>>simply that the blurring is not in the correct, natural distribution
>>>(progression) that a lens would create from that downward looking angle.
>>> Hence it looks artificial in that sense. Our visual BS detector goes off.
>>
>>In addition to that, scenes are 3D, but photoshop work is 2D. So at a
>>down looking angle, there will be vertical objects that are OOF at their
>>base, but in-focus higher up as they cross into the DOF zone. This is
>>lost at a fine level in the image. Even the pole on the right, just the
>>other side of the train, should perhaps be in focus near its top. Our
>>ingrained visual processor just says 'error' without saying why...
>>
>>This image is pretty wide angle as well, looking near vertical at the
>>bottom, and looking near horizontal at the top of the image. This makes
>>it even harder, I suppose, to effect the DOF effect properly.
>
>
> Good points, but in the nature of a rapid magazine tutorial, they
> skipped all the steps where they rubberbanded all the different
> objects based on height....

I don't see at all how it could determine what projected throgh the
focus plane.

Cheers,
Alan


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Anonymous
May 17, 2005 10:55:33 PM

Archived from groups: rec.photo.digital.slr-systems (More info?)

Owamanga <owamanga(not-this-bit)@hotmail.com> wrote:

> My problem with his oversimplification is this: Can a tilt-lens affect
> perspective?

No. Moving the camera in conjunction with using it is what affects the
perspective.

Example: you're pointing your camera up at a building. You don't like
the converging lines, so you want to use a shift to correct for them.
So, in addition to shifting the lens -- you move the camera so it's
not pointing up any more.

> original photo of a life-sized British Rail train at a station, using
> photoshop to introduce a graduated lens blur to the foreground and
> background, the train remained in focus on a horizontal line in the
> center of the image. So, now because of the tight DOF, it looks like a
> toy train. The viewer believes they are a few inches away from the
> train, instead of 150ft away where the original picture was taken -
> so, if I can change the appearance of the camera-to-object distance,
> have I not also altered perspective?

No, you haven't. You haven't altered the apparent camera-to-subject
distance, you've fooled (some) viewers into thinking you have due to
preconditioning in terms of what kind of shots usually have limited
depth of field. You're not exploiting perspective to create the
illusion, you're exploiting expectations.

--
Jeremy | jeremy@exit109.com
!