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Photo Forum / Digital Photography / DSLR Cameras / January 2007Need of mechanical shutter
Okay...so is it really needed for DSLR (or any digital camera) camera ? Why cant you make the 'shutter' with electronics ? Just activate the sensor only for the required time instead of permanently enabling the sensor and using a mechanical device to allow light fall on it ! Or is it done like this in digital cameras ? Jean > Okay...so is it really needed for DSLR (or any digital camera) camera > ? Why cant you make the 'shutter' with electronics ? Just activate the > sensor only for the required time instead of permanently enabling the > sensor and using a mechanical device to allow light fall on it ! Or is > it done like this in digital cameras ? In my Sony A100 there isn't a shutter - the noise that occurs when you take a picture is the mirror flipping out of the way. It's why dust is a problem for some folk :) James >In my Sony A100 there isn't a shutter - the noise that occurs when you take >a picture is the mirror flipping out of the way. It's why dust is a problem >for some folk :) What do other dslrs have? >>In my Sony A100 there isn't a shutter - the noise that occurs when you >>take [quoted text clipped - 3 lines] > > What do other dslrs have? I don't have any first hand experience - I assume something similar, like the OP, I can't really see the point of a physical shutter, but I'm willing to be proven wrong! James >>>In my Sony A100 there isn't a shutter - the noise that occurs when >>>you take a picture is the mirror flipping out of the way. It's why >>>dust is a problem for some folk :) Sorry, that's wrong. >> What do other dslrs have? Most DSLRs use a normal focal-plane shutter, but some use a combination. For instance, the Nikon D50 and D70 use a shutter for speeds below about 1/250, and at or above that the shutter opens but the short exposure time is controlled by the sensor. This has advantages like a higher flash sync speed and a slower shutter motor (lower cost). But it also introduces problems like blooming and grid artifacting since the sensor is trying to control the exposure time. Note that the higher priced Nikon D80 and D200 use only a focal-plane shutter to reduce these problems. > I don't have any first hand experience - I assume something similar, > like the OP, I can't really see the point of a physical shutter, but > I'm willing to be proven wrong! You claim to own the Sony A100 yet you don't even know that it DOES have a focal-plane shutter? That's sad. :-) Oh, and here's the proof from the specs: http://www.dpreview.com/reviews/sonydslra100/page2.asp Scroll down about half way. >>>>In my Sony A100 there isn't a shutter - the noise that occurs when you >>>>take a picture is the mirror flipping out of the way. It's why dust is a [quoted text clipped - 3 lines] > > :-) You know what? I just took off the lens and flipped the mirror and you're right. Last time I did this I could see the sensor though! Maybe I'd locked it in B mode and completely forgotten. You live and learn eh? >>>>> In my Sony A100 there isn't a shutter - the noise that occurs when you >>>>> take a picture is the mirror flipping out of the way. It's why dust is a [quoted text clipped - 7 lines] > right. Last time I did this I could see the sensor though! Maybe I'd locked > it in B mode and completely forgotten. You live and learn eh? Apparently not.... Your manual should be able to tell you a better reason for why you saw the sensor. >>>>> In my Sony A100 there isn't a shutter - the noise that occurs when you >>>>> take a picture is the mirror flipping out of the way. It's why dust is a [quoted text clipped - 7 lines] > right. Last time I did this I could see the sensor though! Maybe I'd locked > it in B mode and completely forgotten. You live and learn eh? One other thing: keep sticking your fingers in there and you *will* have a dust problem, Sony or no Sony. Those anti-dust thingies can only do so much. > I don't have any first hand experience - I assume something similar, like > the OP, I can't really see the point of a physical shutter, but I'm > willing to be proven wrong! > James It depends on the sensor technology. On point-and-shoots it is usual to have CCD sensors that can be left "on" all the time and read out as needed, which means they can give you video recording modes and do away with the mechanical shutter. Most DSLRs have sensors of a similar nature as I understand, the Canon 1D at least has an electronic shutter - in addition to a physical one I think, though I'm not going to dissect mine to find out - that allows it a very fast flash synch time of 1/500 seconds, as I understand it Nikon uses a similar arrangement. Canon DSLRs apart from the 1D does not have electronic shutters though, it seems they can't do this with the CMOS sensors that they use - the 1D uses a CCD, not CMOS. Their flash synch speed is a bit lethargic due to this; there is a limit to how fast they can make the mechanical shutter leaves move up and down. (They do make up for it with low noise at high ISO though.) Part of the reason why a mechanical shutter that physically blacks-out the sensor is still desireable is that it allows the sensor to start "clean" when taking a photo. There's no need to "empty" the sensor first. This also helps to keep temperature down, and in turn gives images with less noise in them. >> Okay...so is it really needed for DSLR (or any digital camera) camera >> ? Why cant you make the 'shutter' with electronics ? Just activate the [quoted text clipped - 6 lines] >for some folk :) >James Is Dpreview wrong? http://www.dpreview.com/reviews/sonydslra100/page2.asp "Electronically-controlled, vertical-traverse, focal-plane Shutter"  SignatureSenate Democrats proposed ethics reform legislation on Tuesday. It calls for lawmakers to pay the real cost of corporate jet flights and the full cost of skybox tickets for sporting events. If you want to know ahead of time what's going to happen to this bill, you simply need to watch the last five minutes of Old Yeller. >>In my Sony A100 there isn't a shutter - the noise that occurs when you >>take [quoted text clipped - 6 lines] > http://www.dpreview.com/reviews/sonydslra100/page2.asp > "Electronically-controlled, vertical-traverse, focal-plane Shutter" No, I was, see my reply earlier in the thread! >> Okay...so is it really needed for DSLR (or any digital camera) camera >> ? Why cant you make the 'shutter' with electronics ? Just activate the [quoted text clipped - 6 lines] > for some folk :) > James It is a problem for very few folk. It is a made-up problem so that some cameras can have a new, useless, 'feature.' > Okay...so is it really needed for DSLR (or any digital camera) camera > ? Why cant you make the 'shutter' with electronics ? Just activate the [quoted text clipped - 3 lines] > > Jean A DSLR has much faster response time than other cameras simply because it has a shutter. It does not have to wait for the sensor to change from viewing and framing mode to shooting mode, nor does it wait for the sensor to power up. The picture is taken when you press the shutter release, not a short time after. It frequently makes all the difference between getting a picture of a bird or an empty twig. > A DSLR has much faster response time than other cameras simply because it has > a shutter. I happen to own an 3MP digital P&S with a mechanical shutter, no, it's not faster than a DSLR. In other words: you are wrong. > It does not have to wait for the sensor to change from viewing and > framing mode to shooting mode, nor does it wait for the sensor to power up. The sensor in a P&S is always powered up, else no viewing. There is also no difference to the sensor between "viewing" and "framing", other that with viewing probably only partial sensor rows are read. > The picture is taken when you press the shutter release, not a short time > after. Please tell us how to flip up the mirror in ZERO time, open the shutter fully in ZERO time, etc. > It frequently makes all the difference between getting a picture of a > bird or an empty twig. Maybe you should investigate into the differences of AF in P&S and DSLR cameras ... -Wolfgang > Okay...so is it really needed for DSLR (or any digital camera) camera No, it is not *needed*, but a mechanical shutter does have a lot of advantages. Investigate into CCD sensors, how they are read out (by pushing charges from cell to cell), that you can push them into opaque rows to read out at leisure, how that "opaque" is not perfect, and so on and so on. > Or is it done like this in digital cameras ? All digital cameras offering "live preview" (video cameras, most P&S cameras, even a very few DSLRs) have an always-on chip (though that is not necessarily the recording chip, see the zigview devices for an example) and of necessicity an electronic shutter (a rotary mechanical wheel shutter is not really saleable these days.) -Wolfgang |
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