“Lock It or Lose It!”
by Bill Debley

No, I’m not talking about the personal items in your car, I’m talking about your camera and image sharpness! Locking up your mirror can prevent the loss of image sharpness. Mirror Lock Up (MLU) is a feature that is often overlooked when using long exposures of <1/60 sec. – several seconds or longer. Although the difference is slight, if you don’t use MLU, it’s enough to degrade you image and you will not have critical sharpness where you want it. In Canon DSLR’s it’s very easy to use but a little harder to find. For example on the Canon 5D you have to go to C.Fn III – 6. I recommend that you use either your 2 sec self-timer or a remote shutter release. With MLU enabled, the first press of your shutter locks the mirror up and exposes the sensor, the second shutter press or when the self-timer times out the shutter exposes the frame.

Manufacturers go to great lengths to minimize the vibrations caused by the movement of the mirror, and yes it is very fast but it does not “slam” or “crash” the inside top of the box as some proponents of MLU suggest. If that were the case it wouldn’t last very long, but the slight vibration can cause a decrease in image sharpness.

If you are a Canon user like me, and you want to use exposure bracketing for HRD or the best exposure, say three shots with the self-timer when you press the shutter it snaps off three shots in succession. Simple right? 

You’ll never guess what happens when you activate Mirror Lock Up with the self-timer or remote shutter cable! MLU negates the firing of all three shots at once and you have to activate the self-timer or remote shutter release for each bracketing setting until you sequence is finished.

How stupid is that? But, there’s an easy solution, use Live View with the 2 second self-timer! In fact, for those shots of 1/60th sec to several seconds simply use Live View with MLU! In Live View the mirror locks up and 2 seconds later the three shots fire off in rapid succession just like without MLU. The same is true for a single photo.

Finally, controlled lab tests using different focal length lenses, shutter speeds, and apertures have shown that with a very stable tripod and ball-head there was no difference in image sharpness with or without Mirror Lock up. Of course, the tripod and ball head costs more that your DLSR and lens.