When shooting using burst mode on a dslr, why does the mirror moves up and down for every photo that is being taken? Wouldn't it be better if the mirror only opens once and the shutter moves for every photo? This would allow the camera to have better burst fps.

On this video we can see how slow the mirror is, when compared to the shutter : https://www.youtube.com/watch?v=wsC8MRiU6GQ


Because in most shooting modes you want the camera to perform Auto Focus and/or metering between each frame. If you are shooting action or sports and your subject is moving towards or away from you AF for each frame is essential. In conventionally designed DLSRs, the mirror must be down to auto focus and to meter.

There are some higher end cameras that allow the end user to elect to shoot the entire burst with the AF and/or metering results of the first frame. This allows the mirror to remain up throughout the entire burst.

  • This is the answer I was looking for. – zguo38953 Jun 7 '15 at 10:22

Mirror moves so that you can track image in real time, framing object better and keeping eye on surroundings. Also, when mirror comes back to normal position, so does AF/AE system.

In some DSLRs (maybe SLRs as well) quick shooting with mirror locked-up (and sometime additional restrictions like locked metering) gives higher frame-rate.

Example is Canon's 1Dx, which is rated at 12 fps at regular settings and 14fps with mirror (and everything else) locked.

In mirrorless cameras you still can track scene via viewfinder because what you see is real captured picture (because viewfinder is electronic)

  • Ok, I didn't know there was an option to lock up the mirror on high-end cameras. – zguo38953 Jun 7 '15 at 10:11

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