On Sharpness, ISO and Shutter Speed

Started Nov 29, 2013 | Discussions thread
Anders W
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Re: Another possible experiment
In reply to ProfHankD, 11 months ago

ProfHankD wrote:

Jack Hogan wrote:

2) Are the dips we see in MTF50 around 1/10th of a second to about 1/300th possibly due to shutter shock - or something else? What implications does this have for people choosing a high resolution camera today?

I'd guess that vibration is a factor here, and imprecision in electronic 1st curtain reset may be the cause of the other issue, but here's a possible experiment to try to resolve this....

In either a focal plane shutter or a not-really-simultaneous-global-electronic shutter, the sensor exposure interval is not really the same for all pixels. Some are exposed earlier and others later, with the overlap fraction dependent on shutter speed. Thus, it should be possible to profile the vibration/movement over time by using multiple targets positioned so that they are exposed in temporal sequence as the shutter travels across the frame. Shutter shock should be an impulse with periodic decay of the vibration over time, which I would expect to cause a measurable pattern in the MTF50 measurements along the shutter's travel direction.... The same test method could also be used to test external damping methods; for example, I'd actually expect human hands to do better damping than a tripod (us humans are after all a type of fluid damping system, right? ).

A more precise test could be made using controlled light pulses, but that's not as easy to do....

I have already conducted an experiment for the purpose of distinguishing between bell-type vibration and brute displacement of the camera as the mechanism whereby shutter action leads to blur. I did so by placing my E-M5 with my most shutter-shock-sensitive lens (Panasonic 100-300 at 300 mm, 600 mm EFL) on a very heavy and rigid surface (my kitchen floor with tiles on top of concrete). This prevents the camera from being displaced but not from vibrating. Result: No sign of blur. So at least in this case, brute displacement rather than vibration is the cause.

Note that I get clear blur due to shutter action in the critical range of shutter speeds when shooting the same combo from my reasonably sturdy tripod (Sirui T-1205X with G-10 head).

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