On Sharpness, ISO and Shutter Speed

Started Nov 29, 2013 | Discussions thread
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Ken Strain
Regular MemberPosts: 369
Re: On Sharpness, ISO and Shutter Speed
In reply to Jack Hogan, Nov 30, 2013

Jack Hogan wrote:

Ken Strain wrote:

These data are puzzling, two features disturb me most:

The spread between H and V gets to about 20% in several of the plots, including the points for the EM5 at 1/4000s.

Yes. That is the EM5 at ISO 6400, where it is very, very noisy - the noisiest of the sample by a fair margin. I mentioned in the other thread that I believe the spread there is due to the data being too noisy for a reliable MTF50 reading. I included it for completeness in case someone saw something else in it, but otherwise I would be tempeted to ignore it as being outside of usable range. I should experiment a bit with noisy images to see if that is indeed the case.

The EM1 plot is the only one that looks somewhat like I would expect if shutter shock were the main cause of the spread, but even here it appears that something else breaks the H-V symmetry with the opposite sign (such that there is roughly 6% discrepancy between the averaged H and V scopes of the 3 fastest speeds)

Fair point, I'd missed that.  Error bars or at least some statement, local to the results, of the random error in the MTF50 result would help.

Yes, I also wonder about that switch. The other camera that shows it is the A7r (but not the A7). Same problem?

I would be very interested to see a series of properly taken images form the EM1 and A7r at these same apertures with shutter speeds from a couple of seconds to 1/4000th every 1/2 stop or so to see whether I could pinpoint the issue.

A better-controlled set of inputs would help: such as two shutter speeds per exposure, two camera orientations per case, to look for AA filter asymmetry,  two camera mounts for each case - at least some variation to change the motion induced by shutter shock without changing other variables, and at least two samples of each camera.  But that becomes a huge task (16 pictures per case - and it would be good to take a few each time).


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