When I last discussed sharpness testing, it was in the context of shutter slap. Before, I’d been working on generalized sharpness testing, in which many sharpness-damaging effects — camera motion, diffraction, lens quality, flatness of field, adapter alignment, etc. — were given the opportunity to create the final result. While I’d like to be able to leave some of these out of the mix, such as field flatness and adapter alignment, when the methodology involves photographing flat test targets, these things come along for the ride, although they can be compensated for by repeated photographs focused on various areas of the target.
I’m still thinking about ways to measure shutter shock independently of everything else, but don’t have a good solution yet. I did try to photograph a laser level pattern, figuring that the beam couldn’t be displaced instantaneously, but however fast it is, it’s too fast to be useful as a way to see the sensor vibrations.
So I’m back to test targets. If you’ll remember from before, the difficulty with test targets was getting a continuous illumination source whose intensity can be varied without much affecting its spectrum, and ideally, a spectrum similar to that of electronic flash. That would allow successive exposures at constant ISO setting and f-stop across a range of shutter speeds. The light source should also be bright enough that exposures at fast shutter speeds can be compared with exposures using strobes, which would be the control.
I am happy to report that I’ve found an appropriate light source. I am not happy with the price, especially since I’ll need two. I’m going to keep looking, and I’d appreciate anyone’s ideas on the subject.