Diffraction Limited Camera Optics

[Jay Gould]

The smallest aperture is not always the best aperture!

While at first glance for us newbies we tend to think that with landscapes we want to stop down to or almost to the extreme, i.e., the smallest f/stop the lens offers. This article from Cambridge In Color addresses the issue of Diffraction Limited Camera Optics: http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm

Even I can understand what they are saying!!

For those that haven't cybered into CIC in the past, there is a wealth of information for you to consider, and, yes, another Forum!

Enjoy; looking forward to everyone's comments.

[John Chardine]

Thanks for the site Jay.

I imagine this can be a particular problem for macro photography where f22 and smaller is SOP. In this case, the camera with the biggest sensor sites will be the least affected. Right now these are the FF Nikons (except D3x) and the 5D mk I.

When I had a 50D I did a few tests around the f-stop where this was supposed to be a problem (around f8 if I remember), and I found very little if any difference in IQ at f11 and f16. I could see an effect at smaller f-stops.

[Don Lacy]

Are smaller pixels somehow worse? Not necessarily. Just because the diffraction limit has been reached with large pixels does not mean the final photo will be any worse than if there were instead smaller pixels and the limit was surpassed; both scenarios still have the same total resolution (although one will produce a larger file). Even though the resolution is the same, the camera with the smaller pixels will render the photo with fewer artifacts (such as color moiré and aliasing). Smaller pixels also provide the flexibility of having better resolution with larger apertures, in situations where the depth of field can be more shallow. When other factors such as noise and depth of field are considered, the answer as to which is better becomes more complicated.
Like all photography their are trade offs and one should use the aperture needed to achieve the image you wish to create. Look thru the marco forum and you will see some of the best images were created at f/16 and higher with cameras that have high MP.

[Mike Moats]

I shoot f/32 on almost everyone of my images where I want everything in focus, yes some slight softness from diffraction but I just add a little more sharpening. Never heard anybody say my images didin't look sharp or see any problems from the extra sharpening. I can't say what happens for the landscape and wildlife photogs shooting stopped down, only what happen with my macro images.

[Mike Moats]

Here's a link to a test on did on a macro image with the difraction issue. Its from my blog back a year or so ago.
http://tinylanscapes.wordpress.com/2009/03/03/diffraction-in-macro/

[Desmond Chan]

I shoot f/32 on almost everyone of my images where I want everything in focus, yes some slight softness from diffraction but I just add a little more sharpening.

I could be wrong, but I think Photoshop and the like has made problems such as the softness caused by diffraction or any ill effect supposedly caused by the use of protection filter no longer an issue these days.

[Mike Moats]

Hey Desmond, most photographers from the film days were affraid of diffraction as they had no recourse to correct it, but you're right with sharpening in photoshop we can add the sharpness back in. Now the larger full frame sensors with the higher megapixel tend to have a little more problems with diffraction and need even more sharpening.

[Roger Clark]

My 2 cents.

Diffraction decreases contrast at the finest scale, and while technically does make things softer, that is not as apparent as the loss of contrast. That loss in contrast versus pixel spacing is shonw in Figure 9 at:
http://www.clarkvision.com/articles/digital.sensor.performance.summary/
And, as people have noted, unsharp mask can recover some of that contrast (although Richardson-Lucy deconvolution will do a better job). But some detail will not recover and the detail is lost. Th loss of
detail and loss of contrast is illustrated in Figure 4 on this page, comparing lines and spots:
http://www.clarkvision.com/articles/sampling1/
Notice howlittle difference there is between f/8 and f/11 (I need to do this test again with a camera with smaller pixels and a less aggressive blur filter, like a 1D4). Note too the blur filter mitigates the differences due to diffraction (by making the fast f/ratios worse).

But in macro photography, and other DOF limited photography, out of focus is more harmful to the image detail than diffraction, so stopping down definitely helps overall image quality even if if blurs the in focus area a tiny bit. Mike's web page shows that nicely.

For macro photography of static subjects, there is a win-win situation: fast f/stops and move the plane of focus making many images and use helicon focus or other software to merge the many frames. Actually works on any DOF limited photography of static subjects. I used varying focus on landscape mosaics to give me the DOF I want.

Roger