Why Mirror Lock-Up is an important feature of your digital SRL camera

If you want to get the most sharpness out of your digital camera, you should use the mirror lock-up feature of your camera for longer shutter speeds.
Most current digital SRL cameras (DSLRs) come with a feature called mirror lock-up. It’s used to reduce the vibrations caused the the mirror in the camera. After you press the shutter button, the mirror flips up before the shutter opens and lets light on the sensor.
This is a mechanical operation that can cause a slight shake inside the camera. It’s not really noticeable from the outside but you often can see it the effect (reduced sharpness) in the final image.
With mirror lock-up (MLU) you can tell the camera to flip up the mirror and then open the shutter only after the camera has “calmed down”. See below on how to best use mirror lock-up.

Here are two pictures taken to show the difference. Both shots are 100% crops of a picture I took today with a Canon EOS 40D and my Canon EF 180mm f/3.5L Macro USM, which is one of Canon’s best lenses. The combination was mounted on a tripod and I used a cable release for all shots. The shutter speed was 1/8th second.

Without mirror lock-up

With mirror lock-up

No sharpening in Photoshop was applied to those picture. If you look closely, you can see that the shot without mirror lock-up is not nearly as sharp as the one taken with mirror lock-up. Of course you could correct it to some degree with Lightroom or Photoshop, but the better the original image, the better the results with Photoshop.

When to use mirror lock-up?

Using mirror lock-up makes sense for all images taken with a shutter speed longer than 1/30th second. For long lenses like super telephoto lenses it makes sense even for shorter shutter speeds.
Because of the delay caused by using mirror lock-up, it’s not useful for moving targets, for example, a slowly swimming duck.
Image stabilization should be turned on (if your lens supports it when used with a tripod) but is not a complete substitute for mirror lock-up.
I use mirror lock-up for all my landscape and macro shots for which I use a shutter speed longer than 1/125th or 1/60th second.

How to use mirror lock-up

The camera must be mounted on a tripod and for best results I recommend using a cable release, as this avoid camera shake caused by the photographer when pressing the shutter button.
An alternative offered by some DSLRs is to use the self timer in combination with mirror lock-up. My Canon EOS 40D allows to set the self timer to 2 or 10 seconds. When I press the shutter (and mirror lock-up is enabled), the mirror flips up and after 2 or 10 seconds the shutter is opened and the image taken.

I hope this helps to make clear that mirror lock-up is an important feature of any DSLR camera. Almost every photographer comes into situations where he or she has to use long shutter speeds. Using mirror lock-up really can make the difference between a successful and unsuccessful picture.

If the manufacturer or the salesman in the camera shop tells you that mirror lock-up is no longer needed in modern cameras, don’t believe him.

Don’t buy a DSLR without mirror lock-up.

Unfortunately using mirror lock-up can be a pain when you need it often because some camera manufactures bury it deep inside the camera menu and you have to press several buttons to use it. But that should not keep you from using it.