fp: 1/8000 sec. shutter vs readout ~1/40 sec. vs flash sync. speed ...

Started 8 months ago | Discussions thread
Buhl213 Regular Member • Posts: 344
Re: fp: 1/8000 sec. shutter vs readout ~1/40 sec. vs flash sync. speed ...

mark-vdi wrote:

I genuinely don't know the answer here, so let me try and explain and will be happy to let somebody explain ...

With a mechanical shutter camera, to get a very fast shutter speed say 1/4000 sec. or whatever in this region, the closing curtain has to follow the opening curtain very closely. That is, the sensor (or in the past, the film) is never fully open. This is why you can't get a flash at this speed. Only a narrow band of the sensor would see the flash. The fastest sync. speed for a flash is defined by the fastest speed the opening curtain can open to show the full sensor area (and hence can be uniformly lit by the flash) and then the closing curtain can close.

So far so good ...

The fp has an electronic shutter that can expose up to 1/8000 sec. For me this means irrespective of the relatively slow read out rate (ca 1/30. or 1/40 sec. or whatever in this region) it must be possible to "turn on" and "turn off" all the pixels in 1/8000 sec. (there is no mechanical trailing shutter ...). That it then takes 1/30 sec. to read out the data is for the exposure and freezing of movement irrelevant (the shot is finished). But if that were to be the case, then that would mean all the pixels can be turned on within 1/8000 sec. so, why can't the flash have a sync. speed much faster than 1/30 sec ... The readout is happening "after the shot" (if that is what the problem is ...)

Anyway, I don't know the answer and would be happy to hear any thoughts ...

All the best, Mark

I have never designed analogue chips so its just a thought, but I would guess you will either have per-pixel-logic to store the charge for a variable length of time, or have to read the charge at an exact time after exposure. The former option is expensive for large sensors, and the latter requires the sensor to be able to offload all information at the same time. So the cheapest solution is to fire and read each pixel sequentially or only "slightly parallel".

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