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06-05-2013, 01:27 PM   #1
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focus peaking for testing the lens sharpness

A few days ago I bought a Vivitar Series-1 24-70mm 1:3.8-4.8 VMC Macro Focusing Zoom manual focus lens. What I noticed when I tested it was that the focus peaking was not so much contrast and expressed as the smc PENTAX-DA 40mm F2.8 XS that I have as kit lens. After a two days shooting I was not happy with the results from the Vivitar. It was not sharp at all. So today I swapped it for SMC Pentax-A 50mm F1.7, where the focus peaking worked fine and was seen quite clearly and with more contrast as my 40XS.
So I am curious If anyone else has noticed a similar dependence between focus peaking and lens sharpnes or it is only my imagination Unfortunately I only have three lenses and I can not verify this observation.

06-05-2013, 01:47 PM   #2
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I personally don;t like this implementation of focus peaking, and it would be much better with an option to select what colors should be used for an indication of in-and out- of focus areas. So instead I stick to zoom on focus function - in manual mode after pressing OK it gives nice closeup of cetral part of image - since I switched to it - I hardly miss the focus anymore.
06-05-2013, 02:30 PM   #3
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The peaking is an indication of contrast, not sharpness; but contrast can make images appear to be sharper. It can be quite difficult to focus a low contrast lens with peaking. Magnification would be a better choice.
06-05-2013, 03:22 PM - 1 Like   #4
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It would really depend on the specific inplementation of peaking. Which I don't know.

A possibility is to highlight pixels where luminosity difference to neighbors exceeds a given threshold. Such an implementation would sense resolution expressed as 10-90% edge rise width (which is closely related to MTF50 resolution).

So yes, it cannot be ruled out that some focus peaking algorithm can be used to judge lens resolution. However, lightning, fstop, distance and field of view then should be kept constant.

06-05-2013, 03:51 PM   #5
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QuoteOriginally posted by falconeye Quote
It would really depend on the specific inplementation of peaking. Which I don't know.

A possibility is to highlight pixels where luminosity difference to neighbors exceeds a given threshold. Such an implementation would sense resolution expressed as 10-90% edge rise width (which is closely related to MTF50 resolution).

So yes, it cannot be ruled out that some focus peaking algorithm can be used to judge lens resolution. However, lightning, fstop, distance and field of view then should be kept constant.
Thanks!
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