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lawman

Measuring diffraction on zooms

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Has anyone done any testing to determine where diffraction becomes noticeable on the 3 TL zoom lenses?  I notice that many posted images were taken at fairly slow aperatures - I have always thought that diffraction becomes an issues with full frame sensors at f8-11 and at faster aperatures with the APS-C sized sensors. Any comments would be appreciated.

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Rules of thumb might suggest that a limitation at f/8 for full frame  translates into the same problem at f/5.6 for APS-C sensors, but I use f/5.6 when I have no need for shallow depth of field in all CL primes and the CL wide zoom and don't see any problem.  With the 55-135 I do use f/8, again without problems.  So if there is a diffraction limit, it seems to be higher up somewhere.  These lenses are also sharp wide open so I suspect most of us explore the other end of the range.

Edited by scott kirkpatrick

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And the diffraction limit will vary with the changing focal length of a zoom lens.

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8 hours ago, scott kirkpatrick said:

Rules of thumb might suggest that a limitation at f/8 for full frame  translates into the same problem at f/5.6 for APS-C sensors, but I use f/5.6 when I have no need for shallow depth of field in all CL primes and the CL wide zoom and don't see any problem.  With the 55-135 I do use f/8, again without problems.  So if there is a diffraction limit, it seems to be higher up somewhere.  These lenses are also sharp wide open so I suspect most of us explore the other end of the range.

This has been my practice as well - I was asking the question because of photos posted on the forum where aperatures in the f13 range were being used a lot and I would have thought this would have been very much in diffraction territory.

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10 hours ago, jaapv said:

They are - but you wouldn't notice it on a web JPG.

Thanks for the replies- I guess you can’t fool physics 😊

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From my tests, there is a little bit of sharpness loss at f/16 on the 55-135 and 18-56. Easily corrected with a bit of sharpening in Lightroom. Below that they seem remarkably good.

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52 minutes ago, Tobers said:

From my tests, there is a little bit of sharpness loss at f/16 on the 55-135 and 18-56. Easily corrected with a bit of sharpening in Lightroom. Below that they seem remarkably good.

Sharpening is contrast manipulation. It does not compensate for loss of resolution or acuity, however, higher edge contrast tricks the eye into a perception of sharpness.

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