Michael Reichmann has published a very interesting article called “Understanding Mirror Lock-Up” on his Luminous Landscape website. The article strongly encourages you to use the mirror lock-up function on your camera (if it has it) to ensure optimum image sharpness. Despite this being accessed through a number of menus as a custom function on the Canon EOS 10D, I intend to follow Michael’s advice in the future. But I won’t be trying this test:

“Here’s a small test that you can do. Set your camera on a firm support, such as a tripod, and then place a small glass of water on the hot-shoe (balance it carefully). Set the exposure time to about 1 second, and once the water is very still press the shutter release.

What you’ll likely see are ripples on the surface of the water. This may be caused by your touching the camera to press the shutter and / or the mirror flipping upwards. If you know how to set mirror lock-up on your camera body, do so, and then do the experiment again, but also instead of pressing the shutter release manually, use a remote release, cable release or the camera’s self timer. See any difference in the ripples?”

Website: Understanding Mirror Lock-Up