Almost sounds like a Ken Rockwell post, doesn't it?
Seriously, though, I realize that there are times when MLU is important (long lenses on tripods, night/low light situations, etc).
Good lighting, sturdy tripod/ballhead, remote switch or timer, then it shouldn't make much of a difference on the image sharpness, correct?
What would be the cut off point, in terms of benefit? A shutter speed that is the reciprocal of the len's focal length?
Mirror slap is an intrinsic vibration source (internal to the camera), and it occurs just as the exposure is being made. Even though a good (heavy) tripod can help damp that a little bit, it's intrinsic - right next to the sensor. My interpretation of that is to always use mirror lockup when on a tripod, unless you're shooting action that precludes it. I'd say the only exception to that is with really long exposures (several seconds), where the duration of the vibration is such a tiny fraction of the total exposure duration that any vibration-induced blur will just be averaged out (and even then, with an exposure that long, what's the point in 'saving' another couple of seconds by not using MLU with the 2-second timer?).
Originally Posted by neuroanatomist
Sounds good, but when shooting action, the shutter speed is likely to be fast enough to give sharp images (e.g., 1/500 sec).
Thus, would a MLU with 1/500 sec on a tripod be a significant improvement for a still shot, vs hand held, in terms of sharpness?
I'm thinking it wouldn't. Sure, intrinsically, the mirror slap will induce vibrations, but will it significantly affect image sharpness? There has to be a diminishing return.
Certain situations (AEB), especially for fast shutter speed requirements, don't lend themselves well with MLU. Timers really slow things down, too, for AEB combined with MLU.
Significantly? I suspect not. Technically, it will affect it to some extent, probably non-linearly depending on the frequencies of the vibration relative to the shutter speed. But the effect may not be detectable in the final image with high shutter speeds, or with very long exposures. I'd guess (and it's completely a guess) that mirror slap would affect the image most with exposures in the 1/100 - 1 second range, and yes, focal length will matter (because the smaller the angle of view, the more sensitive to vibration).
I can tell you that vibrations can affect image sharpness even at high 'shutter speeds' - not based on experience with camera optics, but microscopy. Even with exposures of 2 milliseconds (= 1/500 s) in digital microscopy, the vibration inherent in buildings (HVAC, plumbing, etc.) that we humans can't perceive causes loss of sharpness (in this situation, there's nothing else moving in the optical system - the 'shutter' is electronic). For that reason, my microscopes are on air tables (metal-clad slabs of granite/marble weighing a few hundred pounds, floating on a cushion of nitrogen gas). Just a little more stable than your average tripod. []
But, that's a different application than shooting with a dSLR. In the 'real world' I'd suspect that a fast shutter speed will overcome most of the vibration issue, if not all. I guess my philosophy is that if I'm going to take the effort to set up a tripod and use a cable release or timer, I might as well use MLU as well. If I'm trying to shoot someone or some creature moving around, timing the shot is more important, so that precludes using MLU.
Isn't the mirror already locked up when shooting in live view?
Yes, it is (although I don't know that we were discussing Live View, were we?). [:P].
However, if you're in Live View but using the Quick Mode AF option (vs. Live Mode aka contract detection AF), the mirror will flip down to focus - so unless you've set up back-button AF and removed AF from the shutter release, you'll get a mirror flip when you snap the pic (two, actually, down for AF then back up for image capture).
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