Why do many CMOS mirrorless cameras still use a mechanical shutter instead of only an electronic shutter?
Asked 12/27/2014
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Many mirrorless cameras with CMOS sensors can show a live view and record video electronically, so it seems like they should be able to take still photos without a mechanical shutter as well. Yet many still rely on a mechanical shutter for normal shooting.
What are the practical advantages of a mechanical shutter in CMOS cameras, and what limits electronic shutters for still photography?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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There are CMOS-based cameras with electronic shutters (basically all cameras with video mode have electronic shutters) but the technology does have its limits.
When the camera reads from a CMOS sensor it reads the data line-by-line, not all at once, this means that, if the subject or the camera moves fast enough you can get very interesting effects.
CCD sensor, on the other hand, dumps the content of the entire sensor into a second set of components that are not exposed to the light, the camera can then read the "frozen" image.
Video uses the electronic shutter because:
there's less data to read — so the camera can read it faster (full HD is about 2 megapixels, 4K is more difficult at between 8 and 9 megapixels)
camera designers don't have a choice, a mechanical shutter that can run at 60FPS without breaking will be expensive
For still photos a mechanical shutter is still better.
Note: there are cameras that use the electronic shutter to begin the exposure and the mechanical shutter at the end of the exposure
Originally by user2481. Source · Licensed CC BY-SA 4.0
user2481
11y ago
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Generated from our catalog & community — verify before relying on it.
CMOS cameras can use an electronic shutter, and many do for video or special silent modes. The main limitation is that most CMOS sensors are read out line by line rather than all at once. That creates a rolling-shutter effect: if the camera or subject moves during readout, vertical lines can lean and motion can look distorted.
A mechanical shutter helps avoid that by defining the exposure more uniformly for still photos. It also works better with flash, while electronic shutters often cannot be used with flash reliably.
CCD sensors traditionally had an advantage here because they could transfer the whole image to a shielded storage area, effectively freezing the frame before readout.
Electronic shutters are still useful, but for stills they may have tradeoffs such as:
- rolling-shutter distortion during motion or panning
- flash limitations
- practical shutter-speed limits depending on implementation
So the advantage of a mechanical shutter in many mirrorless CMOS cameras is better image integrity for still photography, especially with motion and flash, even though it adds noise, size, and power use.
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