On Sharpness, ISO and Shutter Speed

Started 8 months ago | Discussions thread
Anders W
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Re: Quite a lot of problem parameters...
In reply to The_Suede, 7 months ago

The_Suede wrote:

Anders W wrote:

The_Suede wrote:

Falk's studies are here, and there's others out there too. He's done some more on the same site too, with other cameras. I also have some accelerometer studies on the older D700 that basically say just the same thing, regarding the time spread of the vibration.

Yes, I am well aware of Falk Lumo's shutter-shock studies since a long time and have done a fair amount of testing in this area myself with my MFT gear, just not quite as ambitious. As you might already be aware, there has been very intense discussion about this matter in the MFT forum during the past year. What I was wondering about was specifically data supporting your contention that modern camera (as opposed to older) have very little mirror-slap impact but more so from the shutter.

Of course, the speed of the shutter-blade movement (and thus its impact) has increased historically from the 1/125 s sync speed offered by the first vertical metal-blade shutters of the 1960s but is currently not as high as when it peaked about year 2000.

I would rather attribute the change to a lowering of the mirror-induced force than to an increase in the shutter induced force.

Total system weight for the average mirror-with-submirror assembly has gone down steadily for the lifetime of the SLR-type camera, as has the inertial mass of the controlling motors/mechanisms. And the motion control systems now almost all have tapered force distributions, allowing air brake formation to supply quite a large bit of the motion stopping power.

When plastics were less understood, heavier and bulkier, and motion control systems were full-power until end-stop impact, mirrors were a major contributor to vibrations affecting the image. Now, on any modern camera, those vibrations have almost died out to zero before the first curtain starts to open - maybe also because we have a better understanding of the needed resonance damping qualities needed in the mirror-box to minimize the effect?

Thanks for developing your thoughts of the changes that have taken place with regard to the mirror-induced forces. What you say makes a lot of sense.

Someone in our astro-group did formal tests with long lenses collar mounted, on starscapes (actually distant point-source lights, not really "stars"...) :), I'll see if I find them, and get back to you.

Thanks.

Don't thank me yet... I'll have to find it first. But I think I know who did it.

I thought that your willingness to search for it merited thanks in its own right.

That was just for two cameras though, but I've found the general theory sound in practice too. Placing a hand on the camera when shooting with long lenses mounted to the collar gives sharper images in the 1/30-1/200s range than using timer release or remote release, something I've found that others that I trust to be reasonably methodical about their photography to concur on.

Yes, I understand the idea. A long FL obviously increases the risk of blur due to any displacement of the camera. And having the support directly under the point where the shutter is should be preferable (from a shutter-shock point of view, not necessarily others) to having it somewhere else, since it decreases the likelihood that shutter action forms part of a moment arm. Such an arm increases the likelihood of blur for reasons outlined here:

http://www.dpreview.com/forums/thread/3496076

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