Rolling/electronic shutter vs mechanical shutter?

Started Sep 24, 2022 | Questions thread
John Sheehy Forum Pro • Posts: 27,387
Re: Rolling/electronic shutter vs mechanical shutter?

Bikeridr wrote:


Apparently I've been registered earlier here as I got message of an existing account while registering. When resetting the password, now the forum indicates I registered today.
Anyway, been "lurking" (and apparently been a member) since 2004, and now I have a question.

I am just curious about the difference between the electronic vs the mechanical shutter.
My Canon EOS R5 ( migrated from Canon EOS 20D, via 5D Mk II to R5) can choose between electronic and mechanical shutter. Shutter speed is the same in both (max 1/8000th of a second).

How come the rolling shutter gives bent lines or variations in the light d.t grid frequency while the mechanical doesn't?

I know that the mechanical shutter "rolls" over the sensor during exposure while the electronical "reads and records" each line during exposure.

Shouldn't the mechanical shutter also give the "rolling shutter" artefacts as it still travels over the sensor?

It does; it is just more subtle than slow-rolling e-shutters. Take the Canon R7; it seems to roll its mechanical shutter pretty fast, something close to 1/400s, one of the fastest around, but its e-shutter takes 1/30s, and this is in the range where a lot of fast-moving pans or subjects can create noticeable distortion.

When shooting with flash and deliberately exceed the sync speed, one can see the mechanical shutter blocking part of the image as first curtain opens and the second curtin follows, making a "slit" over the sensor through the exposure.
How does the readout differ between the mechanical and the electronic shutter?

Readout is always with the second electronic curtain. Every mechanical-shutter exposure is an electronic one, too, it's just that there is no light at the beginning of pixel activation or just before readout, so the mechanical shutter alone determines exposure. During those "dark periods", the pixels pick up a little bit of extra thermal noise which they would not have with an e-shutter of the same exposure time, but it is probably tiny in most cases.

Also, why does the R5 "reduce" to 12 bit in electronic mode while having 14 bit in mechanical. I'm shooting solely in raw format.

The R5 is able to read the entire sensor out in 1/60s, allegedly because of the faster 12-bit readout. It would be slower at 14 bits, most likely.

Sorry for the quirky explanation, English is not my native language.

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