EF 17-40mm L, optimum performance

[geert_de_keyser1]

Hi,

 

I've read a few times here that lenses don't always produce the

sharpest image at the smallest aperture, say f22 for most DSLRs. I'm

shooting a series of wideangle shots with an EOS1DIIN and the 17-40mm

and my ideay was simply to put it on a tripod, use mirror lock up, use

the smallest aperture possible to get overal sharpness out of maximal

DOF. I've read a few times here that whilst that may be the right

thing for film, it's not for digital. Can someone explain 'cos I'm

getting confused. And no, you don't have to explain the difference

between sharpness and DOF to me.

[mike_smith2]

research "diffraction softening"

 

Mike Smith

[erick_kyogoku]

Bob Atkins wrote a good overview of diffraction and optimum aperture <a href="http://

bobatkins.com/photography/technical/diffraction.html">here</a>.

[mike butler]

All lenses are subject to the laws of diffraction. Digital or film doesn't matter. Diffraction

makes itself known upon enlargement. Even LF people try to avoid extreme apertures of f/

45 and more if they can, unless they're making contact prints. A pinhole camera can give

you almost unlimited DOF, but there's a tradeoff in diffraction. I try to keep my 17-40 at f/

11-13.

[pjmeade]

I was very pleased with the results I got on my 20D at as little as f8, with good dof and sharpness.

 

In this shot I used f8 to get very acceptable results: -

 

http://www.photo.net/photo/4341413

 

I would happily use f32 on film using a Tamron 28mm/f3.5, but don't go much above f8-11 for the 17-40.

[dave_trayers]

Here is another excellent tutorial on diffraction limits:<p>

<a href="http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm">http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm</a>

[geert_de_keyser1]

thx a lot to all for your advice

[howard_slavitt2]

Diffraction will start diminishing resolution at between f5.6 and f8.0 for a theoretically perfect lens. So to establish the best fstop to use for a particular use, you need to establish how much DOF you need, and then test the lens from f5.6 (or to be less perfectionist f8, which is the rule of thumb cutoff for diffraction limits) through approximately f16 for full frame to see where the corners are acceptably sharp. By f22 you'll see diffraction clearly on a full frame camera, but you still may prefer larger dof for the tradeoff of overall softness. I can usually see some diffraction at f16, but it wouldn't likely be noticeable to anyone but me looking at it on screen at 100%.

[john_jovic]

F8-11, forget about anything else if you want a good sharp image. Even then it's not exactly stunning, but it is very good!

 

JJ

[sattler123]

I shoot also Large Format and am relatively new to the digital world. The issue of diffraction alsways comes up when you use LF gear - we typically use very small apertures to get the desired DOF. I have decided that diffraction is not an issue for my landscape work - for me it is more important to have the necessary DOF than worry about some softness in the corners - and most people will not even notice it. At least in Large Format photography difraction is blown out of proportion - it is NOT that big of an issue. I have not done any meaningful tests with my 5D yet - so I can't speak for the digi-world.

[justin_goeden]

If focusing at infinity (if I understand it right) you're losing 2/3 of your field of acceptable sharpness. DOF is approximately 1/3 in front of the focus point and 2/3 behind the focus point. If you practice focusing with "hyperfocal distance" or whatever the exact terminology is, then you could in turn focus on more with f/8 than you would at f/22 or f/32 (all movements of LF put aside). It's all in how you focus, not just stopping down as far as you can. GO and buy Canon's TS-E 24mm f/3.5L if you want the most "DOF" (well at least change your focus plane to give the effect of more DOF). Good luck!

[peter_white2]

You don't need anyone else's opinion about this. All you need to do is put your camera on a tripod and make a series of exposures with progressively smaller apertures. Load the images into your computer and line them up side by side on your monitor at 100%. Just use a narrow strip from each exposure to find the point at which diffraction becomes the major factor limiting resolution.

 

Do this with each of your lenses and keep track of the results. Then you'll know what f stop to use with every lens when maximum resolution is the most important criterium.

[sheldonnalos]

I find f/8-11 the best. F/8 for best center resolution, f/11-13 for better corner resolution at the slight expense of center resolution. It's also sharper at the wide (17mm) end and slightly softer at the long (40mm) end.

[j.kivekas]

May be you'd find this one interesting:<p>

<a href="http://www.photozone.de/8Reviews/lenses/canon_1740_4/index.htm">EF17-40 tested at Photozone</a>.