Today’s Question: I don’t know how I never knew about this, but I just learned that my camera has a mirror lockup feature. Should I leave this turned on always?
Tim’s Quick Answer: I only recommend enabling the mirror lock-up feature when you are using a shutter speed that is at (or very close to) 1/15th of a second. At shutter speeds that are a bit faster or slower than 1/15th of a second it is safe to leave this feature turned off.
More Detail: In an SLR camera there is a mirror that diverts the light from the lens away from the image sensor (or film) and up to the viewfinder. This is what enables you to see the view through the lens when configuring a photo. The mirror then moves out of the way for the actual exposure.
The reason the mirror lock-up feature exists is to enable you to compensate for the vibrations caused by the movement of the mirror. When you enable the mirror lock-up feature, you will generally press the shutter release button twice to capture a photo. The first time the mirror will be locked up, and the second time the photo will be captured. This enables you to have the vibrations from the movement of the mirror dissipate before you capture the photo.
When the shutter speed is a bit faster than about 1/15th of a second, the exposure is so short that the vibrations caused by the mirror movement shouldn’t affect your photo. Obviously the faster the shutter speed (the shorter the exposure time) the less this vibration is a factor.
With exposures that are a bit longer than 1/15th of a second, the portion of the exposure that is affected by the vibration will be very minor compared to the overall exposure, and so the impact on the photo will be minimal (or non-existent).
Naturally, you could simply leave the mirror lock-up feature enabled for all photos to ensure the vibrations caused by the movement of the mirror are never a factor. However, it is only with shutter speeds of around 1/15th of a second where this can be a significant consideration.
Note, by the way, that the mirror lock-up feature is addressed in lesson 3 of my “Photo Gear Quick Tips” course, which you can find in the GreyLearning library here: