How useful is the mirror lockup function?

A really easy way to check stability combinations is to mount(tape, rubber bands etc) a small mirror on the front of the lens/lens cap/camera you're checking.
Mont to the tripod,point a light source at the mirror/camera so you have a reflected spot of light on the opposite wall. Trip the shutter & observe the projected light. This will give you some idea of how much vibration is present.

I was surprised to feel that my Olympus OM-1, with the mirror locked up, also had an issue with the camera body trying to "torque" around the shutter opening and closing action. Almost ALL of my SLRs have a highly notable reaction to mirror movement, my Minolta x-700 being one of the worst. The absolute "king of the hill" for reacting against the mirror is my Bronica S2a, while my Nikon N80 is probably the best for NOT reacting to mirror movement.

Handy thing to have. As I found out the first time I had my Mamiya 645 on a tripod. I had been using a Slick U-212 for my 35mm and 6x6 TLR shots and thought it stable enough for my needs. Of course the TLR has a leaf shutter(Rolleicord1V) and thus adds little vibration into the mix and the 35mm cameras were smaller and lighter. The first time I used it with the 645 I forgot to lock the mirror up and when I pressed the cable release the camera shook like a puppy happy to see its owner. I locked the mirror up for the next shot. Little difference. The plastic parts that make up the tripod head of the U-212 are not rigid enough for this type of shutter/camera combo. I pulled out the Bogen I use for my 4x5" and that took care of that. But I still use the mlu when using a tripod.

John Koehrer said:

A really easy way to check stability combinations is to mount(tape, rubber bands etc) a small mirror on the front of the lens/lens cap/camera you're checking.
Mont to the tripod,point a light source at the mirror/camera so you have a reflected spot of light on the opposite wall. Trip the shutter & observe the projected light. This will give you some idea of how much vibration is present.

Click to expand...

I did something similar when testing my Pentax 6X7/tripod/tripodhead combination. I mounted a Laserpointer on the lens pointed against a mirror projecting the dot on the wall just behind me (lightpath=20m). I tried my Mannfrotto 055 (2,6kg) and my 058 (approx 6kg) using the mannfrotto 141 head. There was a lot of mirror slap (approx 15mm) and some shutter slap(less than 5mm). I was surprised to see that it didn't matter which tripod I used butI also learned that the little plastic thing that I used instead of the centercolumn was ....... So now I'm planning to cut the centercolumn down to make lowangleshots possible with it. I will also drill a hole in it so I can use the looptechnique mentioned if needed.
I draw some other conclusions but never mind.
Cheers Søren