# Question about the diffraction limit of sensors



## BruinBear (Oct 12, 2012)

So i was looking up diffraction limits and i noticed that on my crop body, 60D the diffraction limit is f/6.9.

What does this mean in practical terms? If a lens i have is sharpest between f/8-f/11 should i still keep the aperture greater than f/6.9 because of this limit?

Thanks guys


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## neuroanatomist (Oct 12, 2012)

It's not a hard limit at all. For the 60D, f/6.9 is the point at which diffraction _just begins_ to affect sharpness. If your lens is sharpest at f/8-11, then f/9 will likely not look too different from f/6.3.


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## mb (Oct 12, 2012)

How did you find out the limit?
Do you know of a lookup table or a formula?


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## traveller (Oct 12, 2012)

Lens softness is far more noticable than diffraction at medium apertures (i.e. ~f/5.6 - f/8 on APS-C). You'll need very sharp lenses to see the benefit of using larger apertures and you'll certainly notice the softness caused by inadequate depth of field more than diffraction. I'd recommend reading this article by Ctein, which helps put it all in perspective: 

http://theonlinephotographer.typepad.com/the_online_photographer/2011/08/nex-7-diffraction-effects.html

If you're really going to get anal, you'll need a tilt shift lens or a view camera and learn to focus using Scheimpflug principle. 

P.S. - link for a good diffraction calculator (and website in general): 

http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm


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## BruinBear (Oct 12, 2012)

Thanks traveller.

And the f/6.9 i was refering to i found here, on a table about 1/8 of the way down the page.
http://www.the-digital-picture.com/Reviews/Canon-EOS-5D-Mark-III-DSLR-Camera-Review.aspx


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## bvukich (Oct 12, 2012)

Here is a well written, easy to understand post explaining DLA:

http://photography-on-the.net/forum/showthread.php?t=747761


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## Mt Spokane Photography (Oct 12, 2012)

BruinBear said:


> So i was looking up diffraction limits and i noticed that on my crop body, 60D the diffraction limit is f/6.9.
> 
> What does this mean in practical terms? If a lens i have is sharpest between f/8-f/11 should i still keep the aperture greater than f/6.9 because of this limit?
> 
> Thanks guys


Diffraction is a property of lenses, not sensors as your title suggests. Therefore, a 60D does not have a diffraction limit. 
Resolution of a lens depends on the lens design, and will be highest at different apertures for different lenses. However, having a high resolution is only one part of a high IQ. As you stop down, most lenses have reduced distortion, and reduced CA's.
Where a sensor comes in, is that sensors with more resolution can see diffraction better, but it is caused by the lens. 
As you can see in this chart with a 15mp Canon 50D and 40mm f/2.8 lens, the resolution does not vary greatly out to f/8. The Chart below it shows basically the same pattern for the 5D MK II

*40mm on 50D*







*40mm on 5D Mark II*





Now, here is the Canon EF 100mm f/2.8 USM Macro lens. It shows the effects of diffraction really taking hold at f/16 and f/22. 

*100mm on 50D*


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