TUTORIAL: Mirror Lock-up Explained
8 January 2018 | Category: Stills
Unlike mirrorless cameras, DSLRs have a mirror inside that bounces light from the lens into the optical viewfinder. In order to let you see the scene in the viewfinder, this mirror sits between the lens and the sensor. This means that when you’re composing an image in the viewfinder, the sensor can’t receive any light from the lens – even if the shutter is open.
In order for the camera’s sensor to record an image, the mirror has to lift up and the shutter open for the specified exposure time. At the end of the exposure, the shutter closes and the mirror flips back down into place, allowing you to see the scene again through the viewfinder. These mirror movements cause slight vibration and with relatively long exposure times this can introduce some blur into your image.
For this reason, most DSLR cameras have a mirror lock-up feature that allows you to lift the mirror up slightly earlier than normal – before the shutter opens. This gives the vibration time to die down so that the image is recorded with minimal blur.
With Canon DSLRs, mirror lock-up is accessed via the main menu, with Nikon DSLRs like the D5, it’s on the release-mode dial.
Once mirror lock-up mode has been selected, the first full press of the shutter release lifts the mirror while the second trips the shutter. The mirror will flip back down automatically after the shutter has closed. You need to compose the scene and focus the lens prior to pressing the shutter release for the first time as once the mirror lifts, you will be unable to see the scene in the viewfinder and the autofocus sensor will not function as it won’t receive any light.
Nikon Exposure Delay
With many cameras, the pause between the mirror lifting and the shutter firing is dictated by the photographer and the timing of the second press of the shutter release, however, some Nikon cameras have a helpful ‘Exposure delay’ option in the menu which automates the delay. When this mode is selected you don’t need to turn the release mode dial to mirror lock-up and you only need to press the shutter release once.
Canon 5DS and 5DS R Mirror Lock-up Options
It’s especially important to avoid small vibrations with a high-resolution camera and with this in mind, the 50Mp Canon 5DS and 5DS R have a collection of mirror lock-up options to make using it easier. In addition to the standard ‘Press shutter release twice to shoot’ option, there are options that allow you to shoot with a single press with a timed delay to the shutter firing. It’s just a case of selecting the one with the delay that you want.
When to use Mirror Lock-up
It’s advisable to use mirror lock-up whenever a DSLR is on a tripod and the exposure time is slower than about 1/125 sec. This value varies a little by camera, but using 1/125 sec as a cut-off should ensure you get the sharpest images possible.
Ideally when you’re using a two-press mirror lock-up system you should fire the shutter with a remote release to avoid introducing vibration by touching the camera.