DSLR Image Capture vs Video Recording??
I just had a question which has been bothering me for a bit. When DSLRs record video, the mirror is up, therefore blocking the viewfinder. How come the sensor is constantly exposed when recording video (essentially capturing 30 or 60 images per second), but when capturing images, the mirror must expose the sensor for a certain amount of time depending on how the shutter speed is set?
I just wanted an in-depth explanation about the difference in the mechanics and science between image capture and video recording on a DLSR.
If possible, could any of you also tell me how mirrorless differs image capture wise??
I know I've asked some pretty technical questions, but I'd appreciate it if you could help me out a bit!
The mirror assembly in a DSLR is rated for between 50,000 and 150,000 actuations ( actuation = flipping the mirror ).
If you flipped the mirror for every frame of a movie, a shutter rated for 50,000 actuations would manage about 2000 seconds at 25fps before it broke - that's just 33 minutes !
So using the mirror for video is just not practical - you'd be buying a new camera every day for video.
People tend to forget this when they needlessly apply burst modes to every shot, BTW. If you reel off five shots every time you hit a shutter you're wasting four of them, is my view, and shortening the life of your camera. Use burst mode where it's really needed.
This might help explain why the shutter type is important and why :
When shooting video (or using live view in general), DSLR becomes a mirrorless camera. Mirror is locked in up position, viewfinder is blacked out, and mechanical shutter is open. So there is no difference between a DSLR and a mirrorless when in video mode.
Professional cinematography cameras utilized a rotating round mirror with cutouts, placed at 45 degrees into the optical path. Having anything of the sort in an SLR would make it prohibitively bulky.
A camera can use an electronic shutter for both still and video. In this case, the pixels are electronically reset, exposed for a given amount of time, and then read out.
An electronic shutter makes no audible noise, and has no moving parts to wear out.
Alternatively, the camera can use a mechanical shutter. A mechanical shutter is typically more precise in timing. With an electronic shutter -- unless you add extra electronics to the sensor -- the top and bottom are read out at slightly different times, giving a bit of a funny effect. A mechanical shutter also allows the camera to play tricks to reduce image noise. It can, for example, take two shots -- one with the shutter closed, and one open -- and use that to do some calibration.
If you're optimizing for image quality, you therefore go with a mechanical shutter. For video, flipping the shutter 30 or 60 times per second would be impractical. So you go with electronic. It turns out that in video, the quality matters much less than stills too, so it's a good fit.
But there are cameras which use mechanical shutters or video, as well as electronic shutters for stills.
Right! But then why can't you decide to lock up the mirror when you want to do burst mode... Basically can you do burst in live view? Because I watched a video of the mirror mechanism during burst on a D4 and it's just crazy. That's one of the reasons the high end ones cost so much!
Also how does the shutter work on a digital mirrorless camera during burst?