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06-02-2011, 06:45 PM   #1
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Shutter Question

I'm not sure if this is a dumb noob question or not but I am wondering... why have a shutter at all? If the imager is an electronic imager, why not leave it active and simply record what's on the imager at the time the shutter button is pressed. Doing it this way, you eliminate the shutter vibration, you can take pictures almost as fast as possible... and you can raise your shutter speed to almost anything... 1/50,000 of a second anyone??

Seems like the way to go to me so... what is missing from my knowledge (just on this subject anyway)!

06-02-2011, 06:52 PM   #2
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Being able to view the framed scene in *real time* is the reason for a mirror mechanism (I gather that's what you mean when you say 'shutter'). The mirror redirects the image through the viewfinder until the instant the camera needs to take the image, in which case the mirror flips up to permit the light rays to pass through unimpeded onto the sensor or film on the back of an SLR camera. Without the mirror, you have a sensor that is constantly active, leading to heating issues (for one) but mostly, it is actually slower than composing a shot optically (through the viewfinder). And if someone needs a shutter speed of greater than 1/8,000 sec, then that person would be going for a much more specialised camera...
06-02-2011, 07:25 PM   #3
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The circuitry involved for an electronic shutter, with current technology, comes with some significant degradation of image quality. Weird patterns, extra noise, decreased dynamic range. I don't really understand why, that's just what you can read from many sources. Nikon had some cameras that did this. The D70, for example. I still have one, for the novelty of being able to synch my strobes at 1/8000s. Not that I ever do, LOL.
06-02-2011, 11:51 PM   #4
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QuoteOriginally posted by mdbrown Quote
I'm not sure if this is a dumb noob question or not but I am wondering... why have a shutter at all?
1-Sensor has to be charged to be able to sensitive to the light, before you took the picture. Charge levels are in fact sensitivity (ISO) . Before sensor is fully charged it is practically useless.
2-Charging times are unacceptability long for photography, like close to 1 sec.

3-I am not good at electronics at all.

06-03-2011, 01:06 AM - 1 Like   #5
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Eventually all the DSLR will move to electronic shutter. Here is one article that has some answers why it's not done currently.

http://www.steves-digicams.com/knowledge-center/why-digital-cameras-have-mec...-shutters.html
06-03-2011, 02:11 AM   #6
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QuoteOriginally posted by mdbrown Quote
I'm not sure if this is a dumb noob question or not but I am wondering... why have a shutter at all? If the imager is an electronic imager, why not leave it active and simply record what's on the imager at the time the shutter button is pressed. Doing it this way, you eliminate the shutter vibration, you can take pictures almost as fast as possible... and you can raise your shutter speed to almost anything... 1/50,000 of a second anyone??

Seems like the way to go to me so... what is missing from my knowledge (just on this subject anyway)!
That's not the question. All point-and-shoot cameras do it this way - shooting video and saving one frame as a shot. Did you use these P&S cameras? They're soooo slow, and hardly can do 1/1000 of a second.

The P&S sensor is small and can be cooled down more easily than big aps-c sensor. Yup, now you can shoot video with it, but it's 1Mp and 30 fps. That is you use 1/15 or 1/20 of the pixels of your sensor and have a shutter speed less than 1/50. The limitation is the heat and cumulative charge in sensor's elements.

Moreover, there are high-speed video cameras that can 1/50,000 of a second... You can get one... 5 kilos camera for the 5 kilos of cash and 5 kilos of ice to cool it.
06-05-2011, 12:35 PM   #7
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The answer is actually pretty simple. It would significantly lower the quality of the image if it used the same system as P&S cameras + there would be no way to cool the sensor. Yes, there are already cameras that can release the shutter electronically by turning the sensor on and off again (I think the 5D mark II can do that), but it probably doesn't allow as fast shutter speeds. Also I think it's not ready for mass production and probably is really expensive to manufacture.
07-08-2011, 07:53 PM   #8
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QuoteOriginally posted by mdbrown Quote
I'm not sure if this is a dumb noob question or not but I am wondering... why have a shutter at all? If the imager is an electronic imager, why not leave it active and simply record what's on the imager at the time the shutter button is pressed. Doing it this way, you eliminate the shutter vibration, you can take pictures almost as fast as possible... and you can raise your shutter speed to almost anything... 1/50,000 of a second anyone??

Seems like the way to go to me so... what is missing from my knowledge (just on this subject anyway)!

Actually, Sony answered this for me. The new top of the line Sony DSLR uses a pellicle mirror. 30% of the light is reflected up to a meter and the remaining 70% passes through to the sensor which is always active. The viewfinder is an lcd just like the rear display. Makes sense although it seems to me that the 30% reduction in light to the sensor would be an issue. There is no mirror to swing out of the way anymore though. Takes up to 10 images per second... thoughts???

07-08-2011, 11:06 PM   #9
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QuoteOriginally posted by mdbrown Quote
Actually, Sony answered this for me. The new top of the line Sony DSLR uses a pellicle mirror. 30% of the light is reflected up to a meter and the remaining 70% passes through to the sensor which is always active. The viewfinder is an lcd just like the rear display. Makes sense although it seems to me that the 30% reduction in light to the sensor would be an issue. There is no mirror to swing out of the way anymore though. Takes up to 10 images per second... thoughts???
I don't know, but I suspect the new Sony pellicle-mirror cameras will still have a mechanical shutter. Again I don't know, but I suspect a lot of P&S cameras have mechanical shutters. Mine certainly has one.

The way these shutters work may vary. Either the shutter closes when you press the shutter release button, then opens, then closes to complete the exposure, or the sensor is electronically reset and the shutter is closed when the exposure is complete. The second system sounds nicer, but will be more prone to the "blooming" problem which is associated with electronic shutters (i.e. a bright highlight can "bleed" charge over an appreciable area).

Sony's system sounds like a bit of a white elephant to me. To waste 30% of the light through a part-mirror which can get dirty, just so you can have phase-detect AF isn't ideal. Anyway, Fuji have shown that you can put the phase-detect mechanism on the sensor - a much better idea.
07-09-2011, 10:11 AM   #10
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QuoteOriginally posted by m42man Quote
I don't know, but I suspect the new Sony pellicle-mirror cameras will still have a mechanical shutter. Again I don't know, but I suspect a lot of P&S cameras have mechanical shutters. Mine certainly has one.

The way these shutters work may vary. Either the shutter closes when you press the shutter release button, then opens, then closes to complete the exposure, or the sensor is electronically reset and the shutter is closed when the exposure is complete. The second system sounds nicer, but will be more prone to the "blooming" problem which is associated with electronic shutters (i.e. a bright highlight can "bleed" charge over an appreciable area).

Sony's system sounds like a bit of a white elephant to me. To waste 30% of the light through a part-mirror which can get dirty, just so you can have phase-detect AF isn't ideal. Anyway, Fuji have shown that you can put the phase-detect mechanism on the sensor - a much better idea.

If the meter can be integrated into the sensor and still be as fast and as accurate then it seems to me that the SLR should go away... no need for it. You could build a camera smaller, lighter, and capable of far faster continuous shooting without the mirror assembly not to mention simpler and so theoretically more reliable and/or more durable.
07-09-2011, 10:47 PM   #11
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QuoteOriginally posted by mdbrown Quote
If the meter can be integrated into the sensor and still be as fast and as accurate then it seems to me that the SLR should go away... no need for it. You could build a camera smaller, lighter, and capable of far faster continuous shooting without the mirror assembly not to mention simpler and so theoretically more reliable and/or more durable.
Well it's not so much the metering, it's the AF. Currently, non-SLRs use contrast-detect AF in which the ongoing image from the sensor is examined while the lens's focus is adjusted. The camera tries to maximise contrast in a given area of the image - which is absolutely fine, but it does take time. So, in general, contrast-detect AF is slow.

SLRs are able to use phase-detect AF, which operates on exactly the same principle as the split-prism focus aid at the centre of old-style focusing screens. Information from the AF sensors is readily available from the AF sensors, the information is realatively simple to process, and the correct direction for focus iterations is indicated. So, phase-detect AF can be very fast indeed.

Fuji's new sensor is described here:

FinePix F300EXR - a slim & stylish, advanced compact digital camera, with impressive picture quality from Fujifilm UK

The good news is that the sensor in question is a small P&S sensor, so it ought to be possible to offer an even less intrusive system on an APS-C sensor. The bad news is that focus accuracy is much more important with the APS-C sensor, owing to much shallower DOF. We don't yet know how accurate the on-chip phase-detect system is, so we don't know how viable it is for a more "serious" camera.
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