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f/8 is the magic aperture for sharpness

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January 21, 2005 4:51:27 PM

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

According to this page f/8 is much sharper than higher or lower
apertures: http://www.photodo.com/art/Impr13.shtml.
Scroll to the bottom for test shots at f/1,8-f/22

I had no idea. It seems too simple, surely it varies depending on the
lens? The writing is a bit confusing, I think these are the relevant
parts explaining this chart: http://www.photodo.com/pix/art/best_at_8.gif

"In the diagram above with the two curves, the descending curve
symbolizes diffraction. At wide apertures the diffraction is minimal.
The part of the light beam that turns fuzzy is very small. But when you
stop down and the hole gets smaller the diffraction gets worse."

"A lens improves optically when stopped down. At large apertures most of
the glass in the lens is used, resulting in a slight blur caused by
unavoidable imperfections in the lenses. When stopping down you screen
off parts of the lens and use only the central area of it. The optical
picture is more correct and the resolution improves. The ascending
curve, starting at 40, symbolizes this "optical" and theoretical sharpness."

"It's only the light passing closest to the aperture edge that turns off
and becomes fuzzy, so when you are using a wider aperture the percentage
of light that is fuzzy decreases. Small holes result in a lot of
diffraction."

"When a wave passes an edge, it turns slightly. It's called diffraction.
The diameter if the light passing a lens is limited by the diameter of
the aperture. The aperture forms a sharp edge and the light closest to
the edges turns off slightly. The edges of the aperture cause a certain
fuzziness."
Anonymous
January 21, 2005 6:09:03 PM

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

"paul" <paul@not.net> wrote in message
news:UtKdneYdmN_95GzcRVn-gA@speakeasy.net...
> According to this page f/8 is much sharper than higher or lower apertures:
> http://www.photodo.com/art/Impr13.shtml.
> Scroll to the bottom for test shots at f/1,8-f/22
>
> I had no idea. It seems too simple, surely it varies depending on the
> lens? The writing is a bit confusing, I think these are the relevant parts
> explaining this chart: http://www.photodo.com/pix/art/best_at_8.gif
>

Hence the phrase: "f8 and be there..."
Anonymous
January 21, 2005 9:06:27 PM

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

paul wrote:
> According to this page f/8 is much sharper than higher or lower
> apertures: http://www.photodo.com/art/Impr13.shtml.
> Scroll to the bottom for test shots at f/1,8-f/22

It's part right. The real deal is that for most lenses, peak sharpness begins
at about 2 to 3 stops closed from max aperture. So the story is slightly
different for an f/1.4 lens v. an f/3.5 lens or a zoom that starts at f/5.6.
Most lenses are fairly sharp through about f/16.

OTOH, if you don't use a tripod, it is all a very moot point.

It's not a bad rule of thumb to assume f/8 and the differences between f/8, f/11
and f/16 in sharpness are not very discernible in an image that is worth pondering.

There are diffraction limited lenses that are sharp at their widest apertures
and remain sharp for 4 or 5 stops down from there before becoming softer due to
difraction at very small apertures.

Having said all that, composition is usually more important than sharpness, so
choose the aperture for the composition.

Cheers,
Alan

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Anonymous
January 21, 2005 9:54:49 PM

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

On Fri, 21 Jan 2005 13:51:27 -0800, paul <paul@not.net> wrote:

>According to this page f/8 is much sharper than higher or lower
>apertures: http://www.photodo.com/art/Impr13.shtml.
>Scroll to the bottom for test shots at f/1,8-f/22
>
>I had no idea. It seems too simple, surely it varies depending on the
>lens? The writing is a bit confusing, I think these are the relevant
>parts explaining this chart: http://www.photodo.com/pix/art/best_at_8.gif
>
>"In the diagram above with the two curves, the descending curve
>symbolizes diffraction. At wide apertures the diffraction is minimal.
>The part of the light beam that turns fuzzy is very small. But when you
>stop down and the hole gets smaller the diffraction gets worse."
>
>"A lens improves optically when stopped down. At large apertures most of
>the glass in the lens is used, resulting in a slight blur caused by
>unavoidable imperfections in the lenses. When stopping down you screen
>off parts of the lens and use only the central area of it. The optical
>picture is more correct and the resolution improves. The ascending
>curve, starting at 40, symbolizes this "optical" and theoretical sharpness."
>
>"It's only the light passing closest to the aperture edge that turns off
>and becomes fuzzy, so when you are using a wider aperture the percentage
>of light that is fuzzy decreases. Small holes result in a lot of
>diffraction."
>
>"When a wave passes an edge, it turns slightly. It's called diffraction.
>The diameter if the light passing a lens is limited by the diameter of
>the aperture. The aperture forms a sharp edge and the light closest to
>the edges turns off slightly. The edges of the aperture cause a certain
>fuzziness."

For crummy, cheap regular lenses, stopping down always improves
sharpness. This is a shame in a way because the larger the aperture
of the lens, the more true resolution it should have.
The diffraction limit, which imposes the limit on detail seen is
roughly 4.48 arc seconds (smallest detail resolvable) per inch of
lens aperture. So a 1" lens can show detail 4.48 arc seconds across
a 2" wide lens will show detail half that size, 2.24" across, etc.
For instance, given the same quality, a lens with a 4" wide aperture
should yield details twice as small as a lens of 2" aperture.
However, this only applies to lenses with enough focal length to take
advantage of the resolution afforded by aperture. This would
(unfortunately) mean having a focal length = 2500mm for a 4" aperture
lens or 1200mm for a lens with a 2" maximum aperture. This is one way
to reach the diffraction limit for a lens. The only way to provide
that kind of focal lenght for those aperture is to use a telescope
which consists of a "prime" lens (called the objective) and a series
of positive lenses interposed between the camera the the prime lens.
Camera lenses are not designed to approach the diffraction limit, none
of them are made to a high enough standard (1.8th wave accurate or so)
to get to the diffraction limit. However, there have been
(apparently) camera lenses designed to provide maximum sharpness when
at full aperture, some of the "Noct" lenses from Nikon or Leica are
such lenses. However, I don't know if the claims for their sharpness
are true or not.
But getting back to the original concept of stopping a lens down.
Suppose you stop a lens with a 2" wide front lens down to f8. That
means that the focal length versus the aperture is now 8:1. For
a 100mm prime lens with a 2" (50mm) front lens, this means the lens
opening is only 12.5mm across and it's theoretical maximum resolution
is now only 9 arc seconds, far less than if the original 2" aperture
could be used. What you have done by stopping the lens down is
minimize the inherent aberrations in that lens. Sperical aberration
(the inability to focus light entering different areas of the front
lens to the same point) chromatic aberration, astigmatism, coma, etc.
This means that the residual aberrations of the camera lens (on
average) are so bad that you must drastically reduce the aperture to
obtain maximum sharpness. However, because of the limit on focal
length verus aperture in a camera lens, the lens's true resolving
power (even at a small 12.5mm aperture) is never reached.
-Rich
-Rich
Anonymous
January 22, 2005 12:30:21 AM

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

I think it depends on the lens. I've used my 85 1.8 to take some awesome
and very sharp 35mm photos taking advantage of the limited depth of field
the lens provides. Looking forward to getting my new D70 and using the lens
with it. The only thing I'll miss is the up-close-and-personal touch the 85
gave me when I used it for portraits. I'll have to back up a bit due to the
magnification factor.


"paul" <paul@not.net> wrote in message
news:UtKdneYdmN_95GzcRVn-gA@speakeasy.net...
> According to this page f/8 is much sharper than higher or lower apertures:
> http://www.photodo.com/art/Impr13.shtml.
> Scroll to the bottom for test shots at f/1,8-f/22
>
> I had no idea. It seems too simple, surely it varies depending on the
> lens? The writing is a bit confusing, I think these are the relevant parts
> explaining this chart: http://www.photodo.com/pix/art/best_at_8.gif
>
> "In the diagram above with the two curves, the descending curve symbolizes
> diffraction. At wide apertures the diffraction is minimal. The part of the
> light beam that turns fuzzy is very small. But when you stop down and the
> hole gets smaller the diffraction gets worse."
>
> "A lens improves optically when stopped down. At large apertures most of
> the glass in the lens is used, resulting in a slight blur caused by
> unavoidable imperfections in the lenses. When stopping down you screen off
> parts of the lens and use only the central area of it. The optical picture
> is more correct and the resolution improves. The ascending curve, starting
> at 40, symbolizes this "optical" and theoretical sharpness."
>
> "It's only the light passing closest to the aperture edge that turns off
> and becomes fuzzy, so when you are using a wider aperture the percentage
> of light that is fuzzy decreases. Small holes result in a lot of
> diffraction."
>
> "When a wave passes an edge, it turns slightly. It's called diffraction.
> The diameter if the light passing a lens is limited by the diameter of the
> aperture. The aperture forms a sharp edge and the light closest to the
> edges turns off slightly. The edges of the aperture cause a certain
> fuzziness."
January 22, 2005 1:00:24 AM

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

paul wrote:

> According to this page f/8 is much sharper than higher or lower
> apertures: http://www.photodo.com/art/Impr13.shtml.
> Scroll to the bottom for test shots at f/1,8-f/22
>
> I had no idea. It seems too simple, surely it varies depending on the
> lens?

It does. A good lens is best at much larger openings.

And this part of the article shows me it's BS..

"The 50/1,8 lens was focused using the cameras superb auto-focus."

You NEVER use auto focus for lens testing.


Bottom line, test your own lenses. Some medium format lenses need to be
stopped down to f11 to be "their best" some of the newest digital lenes are
best at f4.

--

Stacey
Anonymous
January 22, 2005 2:09:28 AM

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

paul <paul@not.net> wrote in news:UtKdneYdmN_95GzcRVn-gA@speakeasy.net:

> According to this page f/8 is much sharper than higher or lower
> apertures: http://www.photodo.com/art/Impr13.shtml.
> Scroll to the bottom for test shots at f/1,8-f/22
>
> I had no idea. It seems too simple, surely it varies depending on the
> lens? The writing is a bit confusing, I think these are the relevant
> parts explaining this chart: http://www.photodo.com/pix/art/best_at_8.gif

Hmmmm ... I am just as surprised as you. If you have a perfect
circular aperture, then the diffraction is very easy to calculate.
So - thats not a problem. But - it sounds very strange that the
unsharpness due to lens faults should follow some kind of curve
that is similar for different lenses. Are you sure that it is not
first of April? :) 


/Roland
Anonymous
January 22, 2005 11:09:32 PM

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

In message <css1tk$mua$1@inews.gazeta.pl>,
Alan Browne <alan.browne@freelunchVideotron.ca> wrote:

>paul wrote:
>> According to this page f/8 is much sharper than higher or lower
>> apertures: http://www.photodo.com/art/Impr13.shtml.
>> Scroll to the bottom for test shots at f/1,8-f/22
>
>It's part right. The real deal is that for most lenses, peak sharpness begins
>at about 2 to 3 stops closed from max aperture. So the story is slightly
>different for an f/1.4 lens v. an f/3.5 lens or a zoom that starts at f/5.6.
>Most lenses are fairly sharp through about f/16.
>
>OTOH, if you don't use a tripod, it is all a very moot point.

That would depend on your shutter speed, and angle of view. A tripod
can only improve on a 15mm lens at 1/2000 in terms of steadily
maintaining composition and rotation. It doesn't improve sharpness.
--

<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<>
John P Sheehy <JPS@no.komm>
><<> <>>< <>>< ><<> <>>< ><<> ><<> <>><
Anonymous
January 23, 2005 4:44:07 PM

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

On 22-Jan-05 20:09:32, JPS said
>In message <css1tk$mua$1@inews.gazeta.pl>,

>>paul wrote:
>>> According to this page f/8 is much sharper than higher or lower
>>> apertures: http://www.photodo.com/art/Impr13.shtml.
>>> Scroll to the bottom for test shots at f/1,8-f/22
>>
>>It's part right. The real deal is that for most lenses, peak sharpness
>>begins at about 2 to 3 stops closed from max aperture. So the story is
>>slightly different for an f/1.4 lens v. an f/3.5 lens or a zoom that starts
>>at f/5.6. Most lenses are fairly sharp through about f/16.
>>
>>OTOH, if you don't use a tripod, it is all a very moot point.

Just to muddy the waters.... at my last place of work, I foolishly went to
take a group photo without a tripod, this was a cloudy December afternoon.

I was using a D1X with I think a 35-70(?) Nikkor zoom. I usually keep it
at 200 ISO but went to 400 for another stop and ended up using the lens
wide open. The results were pretty horrible, people out of the centre of
the picture were really blurry - and it wasn't a big group ( a frontage of
only 10 people).. I thought it was a "rotating" camera movement but my
colleague (who uses identical kit" said after a similar experience, he
never goes below f8 with a group. I went outside and photographed the wall
at a similar distance to the group shot - on a tripod -same aperture. The
result was the same yukky sharpness (forgive the technical term) off the
centre. I was surprised that a new and well looked-after lens could not
yield an acceptable result in these conditions.

Therefore, in practice I would avoid large apertures like the plague where
definiton off the centre of the image was a factor.




All the best,
Angus Manwaring. (for e-mail remove ANTISPEM)

I need your memories for the Amiga Games Database: A collection of Amiga
Game reviews by Amiga players http://www.angusm.demon.co.uk/AGDB/AGDB.html
January 23, 2005 4:44:08 PM

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

Angus Manwaring wrote:

> On 22-Jan-05 20:09:32, JPS said
>
>>In message <css1tk$mua$1@inews.gazeta.pl>,
>
>
>>>paul wrote:
>>>
>>>>According to this page f/8 is much sharper than higher or lower
>>>>apertures: http://www.photodo.com/art/Impr13.shtml.
>>>>Scroll to the bottom for test shots at f/1,8-f/22
>>>
>>>It's part right. The real deal is that for most lenses, peak sharpness
>>>begins at about 2 to 3 stops closed from max aperture. So the story is
>>>slightly different for an f/1.4 lens v. an f/3.5 lens or a zoom that starts
>>>at f/5.6. Most lenses are fairly sharp through about f/16.
>>>
>>>OTOH, if you don't use a tripod, it is all a very moot point.
>
>
> Just to muddy the waters.... at my last place of work, I foolishly went to
> take a group photo without a tripod, this was a cloudy December afternoon.
>
> I was using a D1X with I think a 35-70(?) Nikkor zoom. I usually keep it
> at 200 ISO but went to 400 for another stop and ended up using the lens
> wide open. The results were pretty horrible, people out of the centre of
> the picture were really blurry...
>
> Therefore, in practice I would avoid large apertures like the plague where
> definiton off the centre of the image was a factor.

That makes sense that the wide apertures are used for single portraits
for an extra blurry background & a fairly soft face. Hmm, now that I
think of it, the people at the edges would be further away than the
middle unless they stood in a semi-circle with the camera at the center.
What's a bit contradictory though is that page says narrow apertures
cause more edge blur due to diffraction across the edge of the narrow
opening. Their diagram indicates this should be much worsse at the edges
and negligible in the center (except at very very small apertures).

Larger apertures (according to them) cause blur due to the larger area
of glass being used introducing more imperfections in the glass,
especially with zoom lenses having more glass in them (is that
correct?). I don't know, if there were slight imperfections in the
center of the glass, that could be badly emphasized too I would think.
Higher quality lenses should have little loss at wide apertures but even
expensive lenses should suffer at small apertures (except in the center).

I'm not very experienced but the f/36 on my D70 is unusually tiny isn't
it? I did this hasty test leaning the camera on a doorway (no tripod):
<http://www.edgehill.net/1/?SC=go.php&DIR=Misc/photograp...;
it's a 28-200 nikor which is rated well considering the huge zoom range
but obviously not the most extraordinary lens. (you will also notice the
hideous sensor dist at f/36 which I pointed out in another thread.
January 23, 2005 4:44:08 PM

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

Angus Manwaring wrote:

>
> Therefore, in practice I would avoid large apertures like the plague where
> definiton off the centre of the image was a factor.
>

If you're using a cheapo zoom lens. A good lens =IS= sharp enough at the
edges wide open, a poor one isn't. But then again a lens that is sharp at
the edges wide open isn't going to be cheap either.

--

Stacey
Anonymous
January 24, 2005 2:00:27 AM

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

paul wrote:
> According to this page f/8 is much sharper than higher or lower
> apertures: http://www.photodo.com/art/Impr13.shtml.
> Scroll to the bottom for test shots at f/1,8-f/22
>

Isn't DoF also an issue? I mean at wider apertures you have shallow DoF
making it difficult to focus accurately as I discovered with a Pentax
Super-Takumar 50mm f/1.4.

The limited testing I did with my Canon dRebel kit lens and the pentax
lens told me the same thing as the photodo test - that the lens is
sharpest from f8-f11. From then on, given enough light I use the lenses
at f8.

- Siddhartha
Anonymous
January 24, 2005 6:23:23 PM

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

Kibo informs me that Stacey <fotocord@yahoo.com> stated that:

>Angus Manwaring wrote:
>
>>
>> Therefore, in practice I would avoid large apertures like the plague where
>> definiton off the centre of the image was a factor.
>>
>
> If you're using a cheapo zoom lens. A good lens =IS= sharp enough at the
>edges wide open, a poor one isn't. But then again a lens that is sharp at
>the edges wide open isn't going to be cheap either.

You can get cheap primes that are that good, though.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
January 24, 2005 6:23:24 PM

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

Lionel wrote:

>>
>> If you're using a cheapo zoom lens. A good lens =IS= sharp enough at the
>>edges wide open, a poor one isn't. But then again a lens that is sharp at
>>the edges wide open isn't going to be cheap either.
>
> You can get cheap primes that are that good, though.
>

=SOME= cheap primes are, many are not. Very few of the 'old skool' fast
lenses are very good wide open on the edges either.

--

Stacey
Anonymous
January 24, 2005 8:39:53 PM

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

Kibo informs me that Stacey <fotocord@yahoo.com> stated that:

>Lionel wrote:

>> You can get cheap primes that are that good, though.
[...]
>
>=SOME= cheap primes are, many are not.

Very true - that's why I said "can get". ;) 

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
Anonymous
January 25, 2005 9:47:40 PM

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

On 23-Jan-05 18:36:31, Stacey said
>Angus Manwaring wrote:

>>
>> Therefore, in practice I would avoid large apertures like the plague where
>> definiton off the centre of the image was a factor.
>>

> If you're using a cheapo zoom lens. A good lens =IS= sharp enough at the
>edges wide open, a poor one isn't. But then again a lens that is sharp at
>the edges wide open isn't going to be cheap either.


Well I'd have expected better performance from a Nikor, and it wasn't a
one-off, as I said my colleague's lens behaved in the same way.

All the best,
Angus Manwaring. (for e-mail remove ANTISPEM)

I need your memories for the Amiga Games Database: A collection of Amiga
Game reviews by Amiga players http://www.angusm.demon.co.uk/AGDB/AGDB.html
!