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f/22
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PostPosted: Sat Nov 03, 2012 6:29 pm    Post subject: Reply with quote
peterqd wrote:
Oh dear, I hope this interesting topic isn't going to be ruined by a rather pointless disagreement.


A discussion on this topic was held recently on one of the Photostock Library forums. The question of how far you can stop down, in order to improve DOF, and obtain acceptable sharpness, with or without sharpening , is one which is of interest to some commercial photographers.


PostPosted: Sat Nov 03, 2012 7:31 pm    Post subject: Reply with quote
Have you tried the calculator I linked to at 11:47 today (see above)?


PostPosted: Sat Nov 03, 2012 8:27 pm    Post subject: Reply with quote
twinquartz wrote:
Have you tried the calculator I linked to at 11:47 today (see above)?

It does not seem to account for diffraction.


PostPosted: Sat Nov 03, 2012 8:29 pm    Post subject: Reply with quote
twinquartz wrote:
Have you tried the calculator I linked to at 11:47 today (see above)?


Thanks for the link. I prefer dofmaster. It tells us explicity which equations it uses. It doesn't include diffraction effects. I assume that Photozone uses the same equations - but who knows ?

The sample pictures shown at the Photozone site are not very good. There is a change in framing/perspective from one to another. The green stuff in the background looks as though it's blowing in the wind. And have they used a lens which has a uniform performance from f/2.8 to f/11 ?


PostPosted: Sat Nov 03, 2012 8:35 pm    Post subject: Reply with quote
I use whatever aperture I think I need and can get the results I want on any piece of my equipment. It really comes from experience.


PostPosted: Sat Nov 03, 2012 8:41 pm    Post subject: Reply with quote
martinsmith99 wrote:
I use whatever aperture I think I need and can get the results I want on any piece of my equipment. It really comes from experience.


+1
I used to be deathly afraid of anything larger than F/5.6 as that is what everyone told me, then I tried it. Even if my sensor is diffraction limited at 5.6, I can still get better resolution on some lenses at f11 f16 as it uses better parts of the glass. It all comes down to what you are after, and I've never seen an image get truly soft from diffraction. even at F32. I'll blow the shot from lack of light before I blow it from diffraction sharpness.


PostPosted: Sat Nov 03, 2012 11:23 pm    Post subject: Reply with quote
Yes you can see the effects of diffraction if you blow up a photo enough and then look closely, a bit like going to an exhibition and then looking at details through a jewelers loupe.

I have seen example shots here (and taken some myself) of very busy subjects taken at f1.X and it is so difficult to see the in-focus bit that the whole thing looks like a big blur.

I think too much emphasis is given to wide open shots and wide open sharpness (or lack of it). Orio quite rightly points out that we have much more in our toolbox.


PostPosted: Sat Nov 03, 2012 11:25 pm    Post subject: Reply with quote
skida wrote:
Yes you can see the effects of diffraction if you blow up a photo enough and then look closely, a bit like going to an exhibition and then looking at details through a jewelers loupe.

I have seen example shots here (and taken some myself) of very busy subjects taken at f1.X and it is so difficult to see the in-focus bit that the whole thing looks like a big blur.

I think too much emphasis is given to wide open shots and wide open sharpness (or lack of it). Orio quite rightly points out that we have much more in our toolbox.


Anyone going to an exhibition and looking at the images through a jewelers loupe is not seeing the big picture Smile


PostPosted: Sun Nov 04, 2012 3:52 am    Post subject: Reply with quote
Bye the way I believe that some lenses behave better stopped down a lot than others.

I'm not sure anymore which lens it was but I guess it was a Pentacon 30/3.5 which looked very smeary - much more than usual diffraction only.


PostPosted: Sun Nov 04, 2012 4:23 am    Post subject: Reply with quote
I've never seen a lens perform worse stopped down, if there was one that did, I suspect it was faulty.


PostPosted: Sun Nov 04, 2012 11:20 am    Post subject: Reply with quote
iangreenhalgh1 wrote:
I've never seen a lens perform worse stopped down, if there was one that did, I suspect it was faulty.

I think that tends to be pixel peepers or for performance charts. I know where most of my lenses work best (at least from charts) but that doesn't mean I only use the `best' settings.


PostPosted: Sun Nov 04, 2012 4:25 pm    Post subject: Reply with quote
Photozone has reviewed the Zeiss Makro-Planar T* 50mm f/2 ZF. The resolution decreases as the lens is stopped down (EDIT ... after f/4 that is). At f/22 it is about one half of the value obtained at f/4. Photozone says ...

Beyond f/8 diffraction is the limiting factor so even Zeiss cannot fool physics.

Zeiss would appear to agree. Dr H H Nasse of Zeiss has written an article called Depth of Field and Bokeh.

On page 18 of the pdf, Dr Nasse shows a table of DOF calculations for the 50mm Makro-Planar. DOF calculations for different working distances and f-numbers are given. Also given are values for a parameter UF defined as ..

UF is the useful f-stop, where an MTF-figure of 10% for 90 linepairs/mm is achieved due to limitations by diffraction.

For a working distance of ~ 5m, representing a reproduction ratio of 1:100, UF~15. UF decreases as the working distance is decreased.

Dr Nasse goes on ....

This means that even with 24MP full frame cameras there is only a very small loss of sharpness that can still be balanced out with digital edge enhancement. Combinations of scale and f-number that no longer meet this requirement are listed in gray in the table.

All the entries (different working distances) for f/22 are in gray.

My interpretation is that if you work with this lens, the 50mm Makro-Planar, at f/22 diffraction will lead to softening which can't be removed by simple sharpening methods.


PostPosted: Mon Nov 05, 2012 4:52 pm    Post subject: Reply with quote
I'm not speaking about a little diffraction-unsharpness, I'm speaking more of a large deacrease in both resolution and clarity, maybe also CAs while stopping down, producing smeary look.

I know that a few lenses have their optimum wide open (CV APO 90/3.5 M39 for example) while already beeing less sharp than other lenses @F5.6 or F8
So not only diffraction is limiting sharpness while stopping down with some lenses


PostPosted: Tue Nov 06, 2012 1:25 pm    Post subject: Reply with quote
ForenSeil wrote:
I'm not speaking about a little diffraction-unsharpness, I'm speaking more of a large deacrease in both resolution and clarity, maybe also CAs while stopping down, producing smeary look.

I know that a few lenses have their optimum wide open (CV APO 90/3.5 M39 for example) while already beeing less sharp than other lenses @F5.6 or F8
So not only diffraction is limiting sharpness while stopping down with some lenses


I'm not sure that I understand - do you have any reviews/numbers ?

Presumably the CV 90mm is very well corrected wide open - f/3.5 is not very wide. If you take the Zeiss 50mm Makro-Planar, move the aperture ring limiter and paint out "2" and "2.8" you can sell it as an f/4 lens. Centre resolution is now a maximum wide open - at f/4 - and declines as you stop down. Border resolution increases a little as you stop down and then decreases. (These observations are from the Photozone link given in an earlier post). So there's no aberration to correct in the centre and resolution declines because of diffraction. At the borders uncorrected aberrations are removed as you stop down - the resolution goes up - and then the effect of diffraction dominates and the resolution decreases.
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