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Depth Of Feild

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Anonymous
February 27, 2005 12:34:40 PM

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

Are the depth of field markers on a 35mm film lens correct when the lens is
used on a DSLR with a 1.6x magnification factor?

If I have a depth of field of three metres to infinity using a 50mm lens on
a film SLR and I put it on a DSLR, does the DSLR still have a depth of field
of three metres to infinity or does the magnification factor impact it?

More about : depth feild

Anonymous
February 27, 2005 12:34:41 PM

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

"Edward Holt" <edward_holt@hotmail.com> wrote in message
news:4221949d$0$32605$db0fefd9@news.zen.co.uk...
> Are the depth of field markers on a 35mm film lens correct when the lens
> is used on a DSLR with a 1.6x magnification factor?
>
> If I have a depth of field of three metres to infinity using a 50mm lens
> on a film SLR and I put it on a DSLR, does the DSLR still have a depth of
> field of three metres to infinity or does the magnification factor impact
> it?
>
-----------
As mentioned before, there are many tutorials and threads pertaining to
your question. Depth of Field and Depth of Focus are commonly misunderstood
terms and much has been written about it.
An excellent (not too technical) source is:
www.luminous-landscape.com

Look under "Tutorials" and "Understanding Series". You will have a better
understanding of what you are looking for.
Regards,
Don F
February 27, 2005 12:56:29 PM

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

"Edward Holt" <edward_holt@hotmail.com> wrote in message
news:4221949d$0$32605$db0fefd9@news.zen.co.uk...
> Are the depth of field markers on a 35mm film lens correct when the lens
> is used on a DSLR with a 1.6x magnification factor?
>
> If I have a depth of field of three metres to infinity using a 50mm lens
> on a film SLR and I put it on a DSLR, does the DSLR still have a depth of
> field of three metres to infinity or does the magnification factor impact
> it?
>
>

No. Look for various threads in this group eg RE: DSLR Depth fo field 10/2
2005 . I learnt a lot from the group, in particuilar that the DOF scale is
only correct for 10x8 print when using 35mm film !
Related resources
Anonymous
February 27, 2005 1:27:33 PM

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

"dylan" <no@nospam.com> wrote in message
news:cvs5h4$54b$1@newsg1.svr.pol.co.uk...
>
> "Edward Holt" <edward_holt@hotmail.com> wrote in message
> news:4221949d$0$32605$db0fefd9@news.zen.co.uk...
>> Are the depth of field markers on a 35mm film lens correct when the lens
>> is used on a DSLR with a 1.6x magnification factor?
>>
>> If I have a depth of field of three metres to infinity using a 50mm lens
>> on a film SLR and I put it on a DSLR, does the DSLR still have a depth of
>> field of three metres to infinity or does the magnification factor impact
>> it?
>>
>>
>
> No. Look for various threads in this group eg RE: DSLR Depth fo field 10/2
> 2005 . I learnt a lot from the group, in particuilar that the DOF scale is
> only correct for 10x8 print when using 35mm film !
>

IMO logic would dictate that the magnification factor is only for your use
in determining what size your image will be. Keep in mind the focal length
of the lens does not change. The image is being "cropped" by a specific
ratio due to the smaller size of the image sensor. It is not being
magnified in any way. Therefore, the DOF should be the same.

As for the second statement: What difference should it make how large you
print your image? The DOF is in the image. The image does not change when
you blow it up, except for size, so how could DOF change? Your image is
only two dimensional. That's like saying if you take a photo of your
daughter and blow it up larger than 8x10 she will become your son.

Somebody correct me if I'm wrong.
Anonymous
February 27, 2005 3:09:04 PM

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

"dylan" <no@nospam.com> wrote in news:cvs5h4$54b$1@newsg1.svr.pol.co.uk:

> I learnt a lot from the group, in particuilar that the DOF scale is
> only correct for 10x8 print when using 35mm film !

Hmmmm ... no ... not really. Look at this ...

http://www.nikonlinks.com/unklbil/dof.htm

It says the CoC is defined as 5 l/mm for a 10x8. This will
result in CoC being d/1625, where d is the diagonal.

But the value 1625 can be used for any size, so - the DOF
scale on your lens is correct for any print size. It is
just to change the viewing distance.

OK - for smaller prints you need a magnifying glass and
vary good photo paper - so there is a limit for smaller prints.


/Roland
Anonymous
February 27, 2005 5:06:44 PM

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

Sheldon <sheldon@XXXXXXXXsopris.net> wrote:

> "dylan" <no@nospam.com> wrote in message
> news:cvs5h4$54b$1@newsg1.svr.pol.co.uk...
> > "Edward Holt" <edward_holt@hotmail.com> wrote in message
> > news:4221949d$0$32605$db0fefd9@news.zen.co.uk...
> >> Are the depth of field markers on a 35mm film lens correct when the
> >> lens is used on a DSLR with a 1.6x magnification factor?
> >>
> >> If I have a depth of field of three metres to infinity using a 50mm
> >> lens on a film SLR and I put it on a DSLR, does the DSLR still have a
> >> depth of field of three metres to infinity or does the magnification
> >> factor impact it?
> >
> > No. Look for various threads in this group eg RE: DSLR Depth fo field
> > 10/2 2005 . I learnt a lot from the group, in particuilar that the DOF
> > scale is only correct for 10x8 print when using 35mm film !
>
> IMO logic would dictate that the magnification factor is only for your use
> in determining what size your image will be. Keep in mind the focal
> length of the lens does not change. The image is being "cropped" by a
> specific ratio due to the smaller size of the image sensor. It is not
> being magnified in any way. Therefore, the DOF should be the same.

DoF resides in the capacity of your eye to see detail in the finished
print, not in the lens. So regardless of what the DoF indicators on the
lens says, different print sizes will result in different DoF.

> As for the second statement: What difference should it make how large you
> print your image? The DOF is in the image. The image does not change when
> you blow it up, except for size, so how could DOF change?

Again, DoF is *perceived,* it is not 'in the image.' If you take a
blurry image and shrink it, the shrunken image will appear to be
sharper. This is because the DoF has *changed.*

> Your image is only two dimensional. That's like saying if you take a photo
> of your daughter and blow it up larger than 8x10 she will become your son.

No, it's like saying that if you take a photo of your daughter and blow
it up larger than [whatever dimensions] it will become an image of your
daughter where the parts that are out of focus will appear much more out
of focus. :-)

> Somebody correct me if I'm wrong.

OK, will do. :-)

(Sorry, I couldn't resist.)
February 27, 2005 7:55:24 PM

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

> Hmmmm ... no ... not really. ...
>

so the reply (below) I got to an early post is wrong then ?

>> Thanks, I understand your argument but still not 100% convinced that's
>> the
> >whole story because how does the DOF scale work on a lens (not that the
> >latest models have them) , it would need to be related to the final print
> >size ?

>Yup. The DOF scale on the lens is based on an assumption that the output
>will be 8x10, 10 inches from your face. It's a safe assumption, too.

Confused !!
Anonymous
February 27, 2005 9:22:25 PM

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

"Edward Holt" <edward_holt@hotmail.com> wrote:

> Are the depth of field markers on a 35mm film lens correct when the
> lens is used on a DSLR with a 1.6x magnification factor?
>
> If I have a depth of field of three metres to infinity using a 50mm
> lens on a film SLR and I put it on a DSLR, does the DSLR still have a
> depth of field of three metres to infinity or does the magnification
> factor impact it?
>
>
>

You'll have less depth of field with the DSLR. People will give you all
sorts of bullshit reasons why this isn't so but experimention bears this
out. It has to do with the difference in sensor size requiring a smaller
COC in order to maintain the same depth of field in indentically sized
prints. You'll get the same DOF that you'd have if you cut the
approprately sized piece out of the middle of one of your film camera
prints and enlarged it to the original print's size. DOF is a nebulous
term and requires that you standardize your print size and viewing
distance before any sort of meaningful numbers for comparison can be
generated.
Anonymous
February 27, 2005 9:22:26 PM

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

Bubbabob <rnorton@_remove_this_thuntek.net> wrote:

> "Edward Holt" <edward_holt@hotmail.com> wrote:
>
> > Are the depth of field markers on a 35mm film lens correct when the lens
> > is used on a DSLR with a 1.6x magnification factor?
> >
> > If I have a depth of field of three metres to infinity using a 50mm lens
> > on a film SLR and I put it on a DSLR, does the DSLR still have a depth
> > of field of three metres to infinity or does the magnification factor
> > impact it?
>
> You'll have less depth of field with the DSLR. People will give you all
> sorts of bullshit reasons why this isn't so but experimention bears this
> out. It has to do with the difference in sensor size requiring a smaller
> COC in order to maintain the same depth of field in indentically sized
> prints. You'll get the same DOF that you'd have if you cut the
> approprately sized piece out of the middle of one of your film camera
> prints and enlarged it to the original print's size. DOF is a nebulous
> term and requires that you standardize your print size and viewing
> distance before any sort of meaningful numbers for comparison can be
> generated.

I think you have confused 'Depth of Field' with 'Field of Vision.'
Anonymous
February 27, 2005 9:28:47 PM

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

"Sheldon" <sheldon@XXXXXXXXsopris.net> wrote:

>
> "dylan" <no@nospam.com> wrote in message
> news:cvs5h4$54b$1@newsg1.svr.pol.co.uk...
>>
>> "Edward Holt" <edward_holt@hotmail.com> wrote in message
>> news:4221949d$0$32605$db0fefd9@news.zen.co.uk...
>>> Are the depth of field markers on a 35mm film lens correct when the
>>> lens is used on a DSLR with a 1.6x magnification factor?
>>>
>>> If I have a depth of field of three metres to infinity using a 50mm
>>> lens on a film SLR and I put it on a DSLR, does the DSLR still have
>>> a depth of field of three metres to infinity or does the
>>> magnification factor impact it?
>>>
>>>
>>
>> No. Look for various threads in this group eg RE: DSLR Depth fo field
>> 10/2 2005 . I learnt a lot from the group, in particuilar that the
>> DOF scale is only correct for 10x8 print when using 35mm film !
>>
>
> IMO logic would dictate that the magnification factor is only for your
> use in determining what size your image will be. Keep in mind the
> focal length of the lens does not change. The image is being
> "cropped" by a specific ratio due to the smaller size of the image
> sensor. It is not being magnified in any way. Therefore, the DOF
> should be the same.
>
> As for the second statement: What difference should it make how large
> you print your image? The DOF is in the image. The image does not
> change when you blow it up, except for size, so how could DOF change?
> Your image is only two dimensional. That's like saying if you take
> a photo of your daughter and blow it up larger than 8x10 she will
> become your son.
>
> Somebody correct me if I'm wrong.
>
>
>

Images are 'perfectly' sharp only at a single distance. As you magnify
the print, objects in front and in back of this plane become unacceptably
unsharp. If you alter your viewing distance so that the image subtends
the same number of degrees as the smaller image, this is effectively
negated. If you don't back off, larger prints have less depth of field
because you're magnifying the COF.
February 27, 2005 10:34:40 PM

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

>
> IMO logic would dictate that the magnification factor is only for your use
> in determining what size your image will be. Keep in mind the focal
> length of the lens does not change. The image is being "cropped" by a
> specific ratio due to the smaller size of the image sensor. It is not
> being magnified in any way. Therefore, the DOF should be the same.
>
> As for the second statement: What difference should it make how large you
> print your image? The DOF is in the image. The image does not change
> when you blow it up, except for size, so how could DOF change? Your image
> is only two dimensional. That's like saying if you take a photo of your
> daughter and blow it up larger than 8x10 she will become your son.
>
> Somebody correct me if I'm wrong.
>

might be useful http://www.dofmaster.com/dofjs.html

PS. I originally didn't believe it either !!
Anonymous
February 27, 2005 11:50:41 PM

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

"dylan" <no@nospam.com> wrote in news:cvsu2j$a89$1@newsg3.svr.pol.co.uk:

> so the reply (below) I got to an early post is wrong then ?

Yes - it is wrong IMHO. Read the web page I gave in my reply.
There is it explained. And as far as I can see - the 10x8 is
just an example. If you use 10x8 and look at it at 25 cm (called
normal viewing distance), then the eye resolution is supposed to
be 1/5 mm. Therefore - this is used as the definition of DOF.
But - if you make a larger print at look at it further away you
get the same figure 1625 - and thus the same DOF. If you make a smaller
print - then it is problems though - and the DOF will in practice
increase.


/Roland
Anonymous
February 27, 2005 11:50:42 PM

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

Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:

> "dylan" <no@nospam.com> wrote in news:cvsu2j$a89$1@newsg3.svr.pol.co.uk:
>
> > so the reply (below) I got to an early post is wrong then ?
>
> Yes - it is wrong IMHO. Read the web page I gave in my reply.
> There is it explained. And as far as I can see - the 10x8 is
> just an example. If you use 10x8 and look at it at 25 cm (called
> normal viewing distance), then the eye resolution is supposed to
> be 1/5 mm. Therefore - this is used as the definition of DOF.
> But - if you make a larger print at look at it further away you
> get the same figure 1625 - and thus the same DOF. If you make a smaller
> print - then it is problems though - and the DOF will in practice
> increase.

You're saying that it's possible for the circle of confusion to be
equivalent if you change the size of the paper *and* the viewing
distance to maintain that relationship between them.

And in that circumstance, yes, the DoF would be the same for the two
prints. However, unless you somehow make it so that the larger image can
only be viewed from a certain distance, the DoF will change as people
get closer to it.
Anonymous
February 27, 2005 11:59:25 PM

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

Crownfield <Crownfield@cox.net> wrote in news:42220EAA.B10@cox.net:

>> Somebody correct me if I'm wrong.
>
> correction: you are wrong.
>

You are both right :) 

The definition is that the CoC is 1/1625 of the diagonal.
Then - it does not matter the slightest how large or
small the print is. The DOF scale on the lens is the same
for all print sizes. This is according to the defintion
of DOF - so - if we are talking about DOF - it does not
matter what print size you have.

But - it does matter in practice what print size you have.
In smaller prints you cannot see small details and when
viewing larger prints you can go nearer. So - the actual
sharpness needed usually change with print size. So - in
practice the definition used for DOF might not be all that
useful - and you could use another CoC. But - this is __NOT__
according to the definition of DOF - it is another value,
maybe more useful in some circumstances.


/Roland
Anonymous
February 27, 2005 11:59:26 PM

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

Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:

> Crownfield <Crownfield@cox.net> wrote in news:42220EAA.B10@cox.net:
>
> >> Somebody correct me if I'm wrong.
> >
> > correction: you are wrong.
>
> You are both right :) 
>
> The definition is that the CoC is 1/1625 of the diagonal.

....of an 8x10 print viewed at 25cm. :-)

> Then - it does not matter the slightest how large or small the print is.

....as long as it's an 8x10 print at 25cm. :-)

> The DOF scale on the lens is the same for all print sizes.

....that happen to be 8x10 viewed at 25cm. :-)

> This is according to the defintion of DOF - so - if we are talking about
> DOF - it does not matter what print size you have.

I think that if you look for more definitions of DoF, you'll find more
accurate information. '1/1625 of diagonal' is only part-way there. It's
like saying that the theory of relativity is equal to 3, because you can
solve e=mc^2 for e=3.

> But - it does matter in practice what print size you have. In smaller
> prints you cannot see small details and when viewing larger prints you can
> go nearer. So - the actual sharpness needed usually change with print
> size. So - in practice the definition used for DOF might not be all that
> useful - and you could use another CoC. But - this is __NOT__ according to
> the definition of DOF - it is another value, maybe more useful in some
> circumstances.

The CoC doesn't change; your eyes' capacity to see detail is really only
going to be affected by disease or old age. Relative to the constant
CoC, the DoF changes as you alter print size and viewing distance.
February 28, 2005 12:31:39 AM

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

"Roland Karlsson" <roland_dot_karlsson@bonetmail.com> wrote in message
news:Xns960ADE372E1C1klotjohan@130.133.1.4...
> "dylan" <no@nospam.com> wrote in news:cvsu2j$a89$1@newsg3.svr.pol.co.uk:
>
>> so the reply (below) I got to an early post is wrong then ?
>
> Yes - it is wrong IMHO. Read the web page I gave in my reply.
> There is it explained. And as far as I can see - the 10x8 is
> just an example. If you use 10x8 and look at it at 25 cm (called
> normal viewing distance), then the eye resolution is supposed to
> be 1/5 mm. Therefore - this is used as the definition of DOF.
> But - if you make a larger print at look at it further away you
> get the same figure 1625 - and thus the same DOF. If you make a smaller
> print - then it is problems though - and the DOF will in practice
> increase.
>
>
> /Roland

Thanks, makes sense now.
Anonymous
February 28, 2005 3:26:58 AM

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

usenet@mile23.c0m (Paul Mitchum) wrote:


>
> I think you have confused 'Depth of Field' with 'Field of Vision.'
>

In what way?
Anonymous
February 28, 2005 4:03:58 AM

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

Technically I agree with Bubbabob. Personally, I've always used the depth
of field preview button and then close down one additional stop for
insurance. It hasn't failed me yet regardless of format. I guess you might
need to use the scale on the lens for really low light photography where
the button is impracticle.

--
Message posted via http://www.photokb.com
Anonymous
February 28, 2005 8:43:18 AM

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

"stephen zimic via PhotoKB.com" <forum@PhotoKB.com> wrote:

> Technically I agree with Bubbabob. Personally, I've always used the
> depth of field preview button and then close down one additional stop
> for insurance. It hasn't failed me yet regardless of format. I guess
> you might need to use the scale on the lens for really low light
> photography where the button is impracticle.
>

I've experimentally determined the same thing. One additional stop seems to
do it.
Anonymous
February 28, 2005 6:05:50 PM

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

Bubbabob <rnorton@_remove_this_thuntek.net> wrote:

> usenet@mile23.c0m (Paul Mitchum) wrote:
>
> > I think you have confused 'Depth of Field' with 'Field of Vision.'
>
> In what way?

On a re-read, I see your point.
Anonymous
February 28, 2005 9:58:20 PM

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

usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsn9ki.mvaks61svhycwN%
usenet@mile23.c0m:

> You're saying that it's possible for the circle of confusion to be
> equivalent if you change the size of the paper *and* the viewing
> distance to maintain that relationship between them.

Yes - that is the definition of DOF.

> And in that circumstance, yes, the DoF would be the same for the two
> prints. However, unless you somehow make it so that the larger image can
> only be viewed from a certain distance, the DoF will change as people
> get closer to it.

Yes - you assume that you don't change the distance.

If you do change the distance - that is a useful meassure - but it is
not according to the definition of DOF.


/Roland
Anonymous
February 28, 2005 10:00:52 PM

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

usenet@mile23.c0m (Paul Mitchum) wrote in
news:1gsnab0.rmkzy015lf8baN%usenet@mile23.c0m:

> Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:
>
>> Crownfield <Crownfield@cox.net> wrote in news:42220EAA.B10@cox.net:
>>
>> >> Somebody correct me if I'm wrong.
>> >
>> > correction: you are wrong.
>>
>> You are both right :) 
>>
>> The definition is that the CoC is 1/1625 of the diagonal.
>
> ...of an 8x10 print viewed at 25cm. :-)

No - no - no - of any print size. The value 1/1625 has nothing
to do with the print size. The 8x10 is just a starting point.

Which make the rest of your reply irrelevant :) 




/Roland
Anonymous
February 28, 2005 10:00:53 PM

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

Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:

> usenet@mile23.c0m (Paul Mitchum) wrote in
> news:1gsnab0.rmkzy015lf8baN%usenet@mile23.c0m:
> > Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:
> >> Crownfield <Crownfield@cox.net> wrote in news:42220EAA.B10@cox.net:
> >>
> >> >> Somebody correct me if I'm wrong.
> >> >
> >> > correction: you are wrong.
> >>
> >> You are both right :) 
> >>
> >> The definition is that the CoC is 1/1625 of the diagonal.
> >
> > ...of an 8x10 print viewed at 25cm. :-)
>
> No - no - no - of any print size. The value 1/1625 has nothing
> to do with the print size.

That might be right, but the definition of CoC is that it's the smallest
practical perceptible angle of human eyesight, at a reasonable reading
distance. That ends up as a certain fraction of a certain size print
held at a certain distance. The fraction varies depending on who you ask
about it, but the fraction is still derived from print size and
distance-from-face.

> The 8x10 is just a starting point.

For what?

> Which make the rest of your reply irrelevant :) 

I never claimed relevance. :-)
Anonymous
February 28, 2005 10:03:40 PM

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

usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsn9po.8ddtiqmgczypN%
usenet@mile23.c0m:

> DoF resides in the capacity of your eye to see detail in the finished
> print, not in the lens. So regardless of what the DoF indicators on the
> lens says, different print sizes will result in different DoF.
>

Nope - DOF is defined to use a CoC of 1/1625 of the picture diagonal.

You might not like the definition. You might like to measure something
else. But - that is not DOF according to the definition.

And - what you proposes cannot be engraved into the lens and is
therefore in practice rather useless.


/Roland
Anonymous
February 28, 2005 10:03:41 PM

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

Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:

> usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsn9po.8ddtiqmgczypN%
> usenet@mile23.c0m:
>
> > DoF resides in the capacity of your eye to see detail in the finished
> > print, not in the lens. So regardless of what the DoF indicators on the
> > lens says, different print sizes will result in different DoF.
>
> Nope

Yup. :-) Try it and see! Find a somewhat fuzzy image, print it out tiny,
and and then big. Put them next to each other on a table. Compare. One
will appear sharper.

> - DOF is defined to use a CoC of 1/1625 of the picture diagonal.

Nope. :-) The markings on the lens *might* *assume* to use that
fraction. DoF isn't defined that way, however.

> You might not like the definition. You might like to measure something
> else. But - that is not DOF according to the definition.

The definition of DoF is this:

The area in front of and behind the image subject which appears to be
sharp.

This means that since a given print with some bokeh viewed from, say, 3
feet away will appear to be more sharp than if you view it 3 inches from
your face, the DoF of that image changes as you move it. Ditto for
resizing. And if you resize *and* move it, then all hell breaks loose.
:-)

> And - what you proposes cannot be engraved into the lens and is therefore
> in practice rather useless.

Ahh! Then you see my point! You don't discard it as incorrect, you
discard it as impractical.

What's engraved into the lens is a safe assumption. And that assumption
is a certain fraction of a print at a certain size held a certain
distance from the face of the viewer. Like I said. :-)

But the reality outside that assumption is not useless, either... For
instance, if I were to get an adaptor and use a medium format lens on my
digital SLR, the lens' DoF indicators would be meaningless (because
they're probably calibrated to something like a print size 5x that of
medium format film, which is huge.). But since I know how DoF actually
works, I can do that math if I need to, and end up with a pretty picture
of the dandelion in the foreground and the mountain range in the
distance, all in focus. More or less. :-)
Anonymous
February 28, 2005 10:05:56 PM

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

"stephen zimic via PhotoKB.com" <forum@PhotoKB.com> wrote in
news:421a8a52c99a4c698d402c7ea14cc14b@PhotoKB.com:

> Technically I agree with Bubbabob. Personally, I've always used the
> depth of field preview button and then close down one additional stop
> for insurance. It hasn't failed me yet regardless of format. I guess
> you might need to use the scale on the lens for really low light
> photography where the button is impracticle.

I have used the DOF markings on the lesns to set the lens
to the hyper focal distance, i.e. you put the farthest 8
(if you use F/8) at infinity.


/Roland
Anonymous
February 28, 2005 10:43:25 PM

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

Roland Karlsson wrote:
[]
> Nope - DOF is defined to use a CoC of 1/1625 of the picture diagonal.
>
> You might not like the definition. You might like to measure something
> else. But - that is not DOF according to the definition.

What does that say about the number of distinctly resolvable pixels which
can be present in the image?

Cheers,
David
Anonymous
March 1, 2005 12:57:04 AM

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

"David J Taylor"
<david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote in
news:xvKUd.25544$8B3.22456@text.news.blueyonder.co.uk:

> What does that say about the number of distinctly resolvable pixels
> which can be present in the image?

Nothing.

DOF is defined with regard to a viewer. It has nothing to do with
film resolution and pixels. DOF is used to evaluate the quality
of a picture. If you print the picture too small or use a to coarse
film or digital sensor, then DOF loses its meaning. If you make
a large enough print and the quality is high - then DOF is meaningful.


/Roland
Anonymous
March 1, 2005 12:08:50 PM

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

Roland Karlsson wrote:
> "David J Taylor"
> <david-taylor@blueyonder.co.not-this-bit.nor-this-part.uk> wrote in
> news:xvKUd.25544$8B3.22456@text.news.blueyonder.co.uk:
>
>> What does that say about the number of distinctly resolvable pixels
>> which can be present in the image?
>
> Nothing.
>
> DOF is defined with regard to a viewer. It has nothing to do with
> film resolution and pixels. DOF is used to evaluate the quality
> of a picture. If you print the picture too small or use a to coarse
> film or digital sensor, then DOF loses its meaning. If you make
> a large enough print and the quality is high - then DOF is meaningful.

Well, I think it does.

By saying that anything 1/1800 of the diagonal cannot be separately
resolved (or whatever the figure is), then it's like saying that anything
1/1500 of the width, or 1/1000 of the height can't be resolved either.
See what I'm getting at? Defining DOF with a particular fraction image
diagonal is implying that there are a particular number of pixels
resolvable in the image as presented to the viewer. I'm not saying it's
1500 x 1000 pixels exactly (would need to do the maths), but I'm sure it's
related.

Cheers,
David
Anonymous
March 2, 2005 12:30:34 AM

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

usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsp619.eux89pf7jmm8N%
usenet@mile23.c0m:

>> No - no - no - of any print size. The value 1/1625 has nothing
>> to do with the print size.
>
> That might be right, but the definition of CoC is that it's the
smallest
> practical perceptible angle of human eyesight, at a reasonable reading
> distance. That ends up as a certain fraction of a certain size print
> held at a certain distance. The fraction varies depending on who you
ask
> about it, but the fraction is still derived from print size and
> distance-from-face.
>
>> The 8x10 is just a starting point.
>
> For what?

As I understand it the definition goes something like this.

1. If you look at a print at normal viewing distance (25 cm),
then a reasonable sized picture to look at is 8x10.

2. At normal viewing distance the resolution is
approx 1/5 mm for normal sight.

3. This will give a resolution to diagonal of 1/1625.

4. If you look at larger prints, then you adjust the viewing
distance so the picture has the same FOV, i.e. the resolution
to diagonal is still 1/1625.

5. If you look at smaller prints, then the DoF really does not
hold. And it is not really important to optimize smaller
pictures for quality anyway.

This leads to the conclusion that 1/1625 is the magic number
for CoC - and then you have a fixed DoF scale on any lens as
soon as you know the sensor size.



/Roland
Anonymous
March 2, 2005 12:30:35 AM

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

In article <Xns960CE4FAEFF9Bklotjohan@130.133.1.4>,
Roland Karlsson <roland_dot_karlsson@bonetmail.com> wrote:
>usenet@mile23.c0m (Paul Mitchum) wrote in news:1gsp619.eux89pf7jmm8N%
>usenet@mile23.c0m:

[ ... ]

>>> The 8x10 is just a starting point.
>>
>> For what?
>
>As I understand it the definition goes something like this.
>
>1. If you look at a print at normal viewing distance (25 cm),
> then a reasonable sized picture to look at is 8x10.
>
>2. At normal viewing distance the resolution is
> approx 1/5 mm for normal sight.
>
>3. This will give a resolution to diagonal of 1/1625.
>
>4. If you look at larger prints, then you adjust the viewing
> distance so the picture has the same FOV, i.e. the resolution
> to diagonal is still 1/1625.

[ ... ]

>This leads to the conclusion that 1/1625 is the magic number
>for CoC - and then you have a fixed DoF scale on any lens as
>soon as you know the sensor size.

O.K. Working from that diagonal, and an 8x10 print (with
presumed 1/4" borders, so it is in reality 7.5x9.5"), we come out with a
diagonal angle of 37.92 degrees, and applying that to the 1625
resolution, it would require a minimum resolution at the camera of
1282x999 pixels to support that (about 1.28 MP) -- and probably better
at double that (as linear dimensions) or four time that as area, so we
need perhaps 5.1 MP to support an 8x10 at the standard viewing distance.
(And actually, a bit more, because some of the picture must be cropped
to fill an 8x10, as the aspect ratio is not the same as the standard
35mm frame of 24x36.

But it would also be the same minimum for a larger print viewed
from the proper distance for that size. So you don't need more than 6MB
unless you are going to be viewing it too closely. :-)

Of course -- if you are cropping more deeply into an image, you
need even more resolution.

Enjoy,
DoN.
--
Email: <dnichols@d-and-d.com> | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
Anonymous
March 2, 2005 11:09:19 PM

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

dnichols@d-and-d.com (DoN. Nichols) wrote in news:D 033du$q5j$1@fuego.d-and-
d.com:

> O.K. Working from that diagonal, and an 8x10 print (with
> presumed 1/4" borders, so it is in reality 7.5x9.5"), we come out with a
> diagonal angle of 37.92 degrees, and applying that to the 1625
> resolution, it would require a minimum resolution at the camera of
> 1282x999 pixels to support that (about 1.28 MP) -- and probably better
> at double that (as linear dimensions) or four time that as area, so we
> need perhaps 5.1 MP to support an 8x10 at the standard viewing distance.
> (And actually, a bit more, because some of the picture must be cropped
> to fill an 8x10, as the aspect ratio is not the same as the standard
> 35mm frame of 24x36.
>
> But it would also be the same minimum for a larger print viewed
> from the proper distance for that size. So you don't need more than 6MB
> unless you are going to be viewing it too closely. :-)
>
> Of course -- if you are cropping more deeply into an image, you
> need even more resolution.

Nothing wrong did I find.

> Enjoy,

Did :) 
!