On Sharpness, ISO and Shutter Speed

Started Nov 29, 2013 | Discussions thread
ferrellmc Regular Member • Posts: 106
Re: On Sharpness, ISO and Shutter Speed

Bernard Delley wrote:

Thanks for your quick and precise answer. And sorry for my slow reply.

I feed MTFMapper the two slanted edges separately (labeled Horizontal and Vertical in the graphs), in the form of TIFFs cropped from the grayscale full resolution image obtained by clipping to zero and white balancing the relative Raw data. The data thus obtained is undemosaiced and as raw as it gets - you can read a bit more about my procedure here . Keep in mind that it only works with neutral subjects lit by a well behaved illuminant (such as D50)

What did you find out with your tests?

I have been looking into PAF behavior like accuracy, repeatability, focus shift, AF tuning and AF color sensitivity using MTFMapper profiles. The trouble is to provide a clean data set supporting a clear message that will not be misunderstood. -- It gets too time consuming to do it. -- I may post focus shift data in a new thread later today.

In this thread we have the riddle of 20% difference between vertical and horizontal resolutions occurring one way with A7 and the other way around with D610. Obvious possible causes include vertically running shutter shake, decentered lens, misaligned Bayer filter etc. The A7r at 1/200s seems consistent with vertical shutter shake.

One would wish further investigation to confirm the effect and narrow down on possible causes; or dismiss the effect as not repeatable. 'Easy' to do for somebody with a camera in question (not me) and prepared with MTFMapper; just set up a single slanted edge against a uniform background (perhaps blue or overcast sky) and analyze the images.

Would it make any sense to shoot an image with no shutter shake and remove that as a variable? Set up the camera in a dark room, set the timer for 10s and fire some off camera strobes at 7s - enough time to allow any shutter vibrations to dampen.

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