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vibration in cameras
These comments apply very generally to all SLRS.
The mirror slap on an SLR causes a damped vibration that damps out after around 20ms or 1/50s. There is some variation of amplitude and damping time between camera models but 20ms is a reasonable average.
A 1/50s exposure or 1/60s is the closest on most cameras is obviously going to capture a large % of the vibration amplitude. There is a small delay between pressing the shutter release and the shutter opening. Part of this is a delay between the mirror flip and the shutter opening that cuts out part of the vibration. Mass market demands minimal delays between shutter press and exposure so manufacturers can't allow too big a gap to keep the delay to a minimum.
Faster exposures and slower exposures are progressively affected less and less.
If the vibration lasts for 1/50s and you make a
1/30s exposure, 60% of the light will be subject to the vibration.
1/15s exposure, 30% of the light will be subject to the vibration.
1/8s exposure, 15% of the light will be subject to the vibration.
1/4s exposure, 8% of the light will be subject to the vibration.
1/2s exposure, 4% of the light will be subject to the vibration.
1s exposure, 2% of the light will be subject to the vibration.
2s exposure, 1% of the light will be subject to the vibration.
and so on.
As exposures get longer on fainter objects, the vibration is progressively underexposed.
As you go faster and faster, the exposure only captures smaller and smaller parts of the vibration.
Shutters still impart some vibration. Mirror lock up(MLU) is useful for some things. For a single manual astronomical exposure, the top hat or black card method is the most effective. For a computer controlled set of subs then there is some merit to use of MLU however longer 30+s subs should not show much effect from mirror slap.
The only application I can think of where you would make multiple subs in the 1/125-1s range are lunar and solar eclipses.
Obviously MLU is worth using if you have it, but a camera without is still highly useable particularly with subs longer than 1s.
Joe
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