On Sharpness, ISO and Shutter Speed

Started 11 months ago | Discussions thread
Anders W
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Re: On Sharpness, ISO and Shutter Speed
In reply to Austinian, 11 months ago

Austinian wrote:

Anders W wrote:

Austinian wrote:

Anders W wrote:

External damping does help. Put the camera on a heavy and perfectly rigid surface (like for example a stone floor) and you won't see any sign of shutter shock even with lenses far more sensitive to the problem than a short tele. I have tried it with my Oly E-M5 and Pany 100-300 at 300 mm (600 mm EFL) and see no problem at all under those conditions. When shooting the same combo from a reasonably sturdy tripod, however, I can't get blur-free images in the critical range of shutter speeds (about 1/25 to 1/250 with the peak about 1/100 or slightly higher).

Interesting. I'm guessing the camera isn't actually attached to the stone floor (as it would be for a tripod), so I wouldn't think it would provide much internal damping.

Correct. That's the point of the test. It rules out displacement of the body as a whole but it does not rule out what we might refer to as bell-type vibration.

Perhaps the vibrations really are causing whole-camera movement, rather than my original notion of sensor-only movement.

The tests I am aware of suggest that bell-type vibration isn't involved at all, at least not as a rule (exceptions may exist with certain specific pieces of equipment). Rather, the blur occurs because of displacements of the body in direct response to the way the shutter blades move and stop inside the camera. When these displacements are completely prevented, as they are with the camera on a very heavy and rigid surface, there is no blur.

Your info opens up a good deal of speculation on my part; would the problem be minimized by hand-gripping the tripod and camera (with consequent damping),

No, since the mechanism is not that of bell-type vibration.

and/or by leaving the IBIS on even when using a tripod?

Based on my testing, there is no evidence that IBIS (of the type used in the E-M5 and some later Oly bodies) misbehaves as a result of vibration when used on a tripod. While the manual recommends that you turn it off when shooting from a tripod, I have seen no ill effects from forgetting to do so, as I sometimes have, even in cases where I was shooting specifically for the purpose of sharpness testing.

On the other hand, I have seen no evidence that IBIS helps against shutter shock either. Regardless of whether you shoot hand-held or on a tripod, the evidence I have suggest that IBIS doesn't exacerbate the blur due to the shock but doesn't help against it either. The reason why it does not help is in all likelihood that the displacements involved are faster than the range the IBIS system can handle.

This is all rather a surprise to me. I wouldn't have thought that the forces involved in shutter opening/closing would have been enough to physically move the entire camera, since I understood that shutters themselves were quite light. The forces in the rest of the mechanism must be considerable though, I guess.

You are right that the shutter blades are very light (probably no more than a gram or so). But they are accelerated up to considerable speed (on the order of 10 meters per second) within an extremely short time and the force responsible for this acceleration as well as the momentum passed on to the body when the blades come to a sudden halt (even more sudden than the very brief acceleration phase) must by physical necessity affect the entire camera body. The only case in which we can be sure that their impact is too small to cause any displacement worth worrying about is when the camera is placed on a very heavy and rigid surface, like the one I mentioned.

I have found one instance where the stabilization system is indeed able to counteract the shock: the OIS on my Panasonic 14-45/3.5-5.6. Since the OIS on this lens is also about as effective as the E-M5 IBIS, shutter-shock aside, I use OIS rather than IBIS when I have this particular lens mounted.

This appears to be a rather special case, however. I have found no evidence that the OIS on the other two OIS lenses I have (Pany 45-200/4-5.6 and 100-300/4-5.6) help against shutter shock. Rather, just like IBIS, it neither hurts nor helps.

Shutter-shock issues aside, there may be instances where it is a good idea to leave the stabilization system on in tripod-based shooting. If you have trouble with the wind, for example, the displacements involved may well be slow enough for the stabilization to cope with them. This is not something I have tried to test however.

Thank you for all this info.

Turning off the stabilization on my A57 requires a menu change which I seldom remember to make. I have not noticed any problems yet on test shots.

Jack Hogan has brought up some really interesting issues in this thread, but I'm clearly out of my depth here as far as figuring out what's actually happening is concerned.

I wish I wasn't, because some of the possibilities (less vibration with smaller sensors/shutters for a given camera weight?, strange manufacturer inattention to this issue?, need for electronic first-curtain?) have some fascinating implications for our cameras.

And that's without even thinking about the horizontal/vertical differences on the A7 and D610...

I'll be lurking and learning with great interest.

 Anders W's gear list:Anders W's gear list
Panasonic Lumix DMC-G1 Olympus OM-D E-M5 Olympus E-M1 Panasonic Lumix G Vario 14-45mm F3.5-5.6 ASPH OIS Panasonic Lumix G Vario 7-14mm F4 ASPH +21 more
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