I was thinkig about real velocity of shutter curtain. I guess that vertial curtain velocity does not change and changes just timing of second curtain release. It means that slot between curtains travels at constant speed, but width of slot depends on shutter speed set up. The amount of light reaching the sensor is the same as shutter would have been fully opened for a very short time, e. g. 1/8000 s. Are my thoughts correct? If yes, how fast the curtain could travel?
Vertical curtain velocity
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millan said:
At fast shutter speeds with a focal plane shutter, the shutter is never 'fully opened'. Instead, the second curtain starts moving before the first curtain completes its traverse, so in effect there's a 'moving window' between the curtains – that window gets narrower as shutter speeds get higher. The fastest shutter speed at which the sensor is fully exposed (first curtain finishes before second curtain starts) is the camera's Xsync speed – the flash duration very short, so the whole sensor must be exposed when the flash fires. From that, you can tell that the 6D (1/180 s Xsync) moves slower than the 5DIII (1/200 s) which is slower than the 1D X (1/250 s). Crop sensor can cameras have higher Xsync because the distance the curtains travel is less (1/250 s for 7DII, 1/300 s for 1DIV).
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Hi Milan.
To answer your first question, it looks like you understand the operation, yes the width of the slot is the equivalent of the shutter exposing the whole sensor for e.g. 1/8000th of a second. As Neuro has explained the longest fully open I'll leave it there. As for how fast, others already gave the numbers for that.
Cheers, Graham.
To answer your first question, it looks like you understand the operation, yes the width of the slot is the equivalent of the shutter exposing the whole sensor for e.g. 1/8000th of a second. As Neuro has explained the longest fully open I'll leave it there. As for how fast, others already gave the numbers for that.
Cheers, Graham.
millan said:
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BozillaNZ said:
Yeah. I really don't understand why camera tech took such a huge step backwards, going from electronic shutters to leaf shutters. Global electronic shutters are clearly far better than anything you can do mechanically. And if we had it on modern sensors with low enough noise, we could just stop caring about ISO entirely. Sample the sensor several times, sum the values, and you're no longer limited by the bit depth of the ADC or the full well capacity of the sensors. Instant high ISO DR. Instead, we're stuck with these clunky mechanical things that fail whenever it is most inopportune....
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dgatwood said:We don't read out CMOS sensors in the dark when using them for video, so obviously that's not essential. I'm pretty sure the real answer is that it's cheaper to toss a leaf shutter in than to do it right....
That's where you get the rolling shutter artifacts. The shutter is required to get one image without much of a time component messing with it. Once you manage to read the sensor fast enough that stops being a problem, at least for usage w/o flash - but until then you need either a bucket brigade or as recently suggested an electrochrome layer.
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dgatwood said:neuroanatomist said:
We don't read out CMOS sensors in the dark when using them for video, so obviously that's not essential. I'm pretty sure the real answer is that it's cheaper to toss a leaf shutter in than to do it right....
As Lawliet correctly points out, there's a good reason why the sensor is read out after the mechanical shutter closes. Maybe you wouldn't mind being limited to slow shutter speeds, but for those of us who need to stop action, eliminating the mechanical shutter is not a tenable solution. As readout electronics and speed improve we will eventually get to a global electronic shutter for dSLRs, but we're not there yet.
Also, as I stated previously, Canon dSLRs do not use leaf shutters.
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Lawliet said:dgatwood said:We don't read out CMOS sensors in the dark when using them for video, so obviously that's not essential. I'm pretty sure the real answer is that it's cheaper to toss a leaf shutter in than to do it right....
That's where you get the rolling shutter artifacts.
You get rolling shutter artifacts because Canon's CMOS sensors don't have a global electronic shutter. The way a global electronic shutter works is pretty straightforward: in a single parallel operation, you shift the values of every pixel into a buffer. Then, you read the buffered values at your leisure. There's no rolling shutter problem, because the readout occurs simultaneously across all the pixels.
A global electronic shutter is significantly better than a focal plane shutter in every way. Even focal plane shutters exhibit a small amount of roll, whereas a global electronic shutter behaves more like a traditional round leaf shutter outside the focal plane, exposing the entire sensor at once and ending that exposure at once. And unlike either leaf or focal plane shutters, global electronic shutters are almost infinitely fast, so you can stop worrying about flash X-sync speed.
And, of course, they're more reliable....
neuroanatomist said:
We should be there. There's no reason you can't do global electronic shutters with CMOS. Several companies have been building CMOS sensors with GES for years. It has nothing to do with speed, and everything to do with simply deciding that the GES is worth the extra sensor fabrication cost and complexity.
neuroanatomist said:
Sorry, I meant focal plane shutter. Terminology fail.
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