usccharles Posted February 17, 2008 Share #1 Posted February 17, 2008 Advertisement (gone after registration) sorry if this is a stupid question.. why do we even need a shutter mechanism? cant they design the sensor to go 'on' 'off' based on the needed 'shutter speed'? i'm sure i'm missing a big chunk here, but isn't a sensor just a gizmo that takes in light when turned on and not take in light when turned off? then couldn't the 'shutter speed' be handled by turning the sensor on and off for the right shutter value than using a mechanical shutter to do so? someone help this ignorant sap. thanks Link to post Share on other sites More sharing options...
Advertisement Posted February 17, 2008 Posted February 17, 2008 Hi usccharles, Take a look here why the need for shutter?. I'm sure you'll find what you were looking for!
adan Posted February 17, 2008 Share #2 Posted February 17, 2008 Several aspects to this: First - a shutter does things besides time the exposure. It keeps dust away from the sensor except for the instants light has to get through (and dust is still a problem - imagine how much more there would be if the sensor was constantly uncovered, including during lens changes.). It also protects the silicon from getting burned by sunlight. Finally, the dyes that color the pixels in a Bayer pattern likely would fade faster exposed to light constantly, whereas with a shutter even 15,000 exposures a year (average 1/60th sec.) add up to only 4 minutes and a bit. Secondly, what sensors DO is release electrons based on the inflow of photons. The electrons, as a voltage, are what flows off the sensor as an image. Some sensors are designed to produce a constant flow of varying voltage, and a "snapshot" of one instant in that flow can be grabbed by circuitry. Any camera with live view does this, including pure video cameras. Other sensors don't output a constant flow, but instead turn on in the dark, collect photons-as-electrons for the duration they are uncovered, and then dump that single "image" once the shutter closes - obviously still quickly, since some shuttered cams can capture and dump 8-10 times per second. I have no expertise at all in why the second kind of sensor is still used, with a shutter, in detail. I suspect there are image-quality considerations (less contamination of one pixel by electrons from the neighbors, heat build-up if the sensor is ON all the time). I'm sure someone here knows that background. This covers about the same ground I did, but perhaps a bit clearer and with more detail - and at least the title addresses your question directly: Steve's Digicams - Tech Corner - September 2007 Link to post Share on other sites More sharing options...
therightagent Posted February 17, 2008 Share #3 Posted February 17, 2008 This must be thinking outside the box. If it works, Leica should pay you big buck!!! I agree with you totally. Link to post Share on other sites More sharing options...
JWW Posted February 17, 2008 Share #4 Posted February 17, 2008 From what I understand, without the mechanical shutter, the electronic sensor will be overwhelmed with too many photons (energy) that has to go someplace. If the sensor electronics cannot dissipate that energy somewhere, then it will appear as noise, streaks, or blooming. Jan Link to post Share on other sites More sharing options...
usccharles Posted February 17, 2008 Author Share #5 Posted February 17, 2008 if the main reason for a shutter mechanism is too-much-light-damages-the-sensor-issue, it would be nice if the shutter was instead a type of sensor cap that keeps the sensor covered while not in use, and when one needs to use it, you press a button, and like mirror-lock, the shutter pops open, except its always open, shutter speed exposures controled by the sensor itself, until one decides to cover the sensor again when not in use. imagine a M8 with no shutter vibrations... i'm sure theres more than that, but wishful thinking Link to post Share on other sites More sharing options...
stunsworth Posted February 17, 2008 Share #6 Posted February 17, 2008 ...imagine a M8 with no shutter vibrations... I thought that's what we already had? Certainly I've never found shutter vibration to present a problem - in fact I've never noticed it when using the camera. Link to post Share on other sites More sharing options...
usccharles Posted February 17, 2008 Author Share #7 Posted February 17, 2008 Advertisement (gone after registration) I thought that's what we already had? Certainly I've never found shutter vibration to present a problem - in fact I've never noticed it when using the camera. well if not vibration, imagine a M8 with no shutter noise~ ! Link to post Share on other sites More sharing options...
dugby Posted February 17, 2008 Share #8 Posted February 17, 2008 This thread begs the question....... So how is the principle of the D2 and it's sensor arrangement different than that for the M8 ? (apart from the obvious..... fixed lens, 5MP versus M-mount, 10MP type information) Link to post Share on other sites More sharing options...
sandymc Posted February 17, 2008 Share #9 Posted February 17, 2008 You can easily build a sensor that doesn't need a shutter - problem is that what it needs is a separate charge store, and the circuitry to transfer charge from the sensor well to charge store next to it. So what you end up with is for the same size sensor and same number of pixels, light gathering capability maybe 2 stops less than a conventional sensor. Also, the charge move usually generates noise of its own, so you end up with a sensor that is, size for size, maybe 2-3 stops less sensitive. Also, because the charge transfer takes a finite amount of time, you can get smear effects for fast moving subjects. For top-end cameras, not a worthwhile trade-off. And BTW, most live-view SLRs actually have a separate sensor in the prism housing doing the live-view sensing, rather than using the main sensor. Sandy Link to post Share on other sites More sharing options...
marknorton Posted February 17, 2008 Share #10 Posted February 17, 2008 In the Digilux 2, the image is captured as a snap-shot but the sensor has to be covered up while the image is read out of the sensor. So the click you hear is the sensor being covered by a crude flap shutter after the capture, not the sensor being exposed, which is one reason why getting the timing right on a D2 is something of a hit and miss affair. Link to post Share on other sites More sharing options...
Guest jimmy pro Posted February 17, 2008 Share #11 Posted February 17, 2008 Maybe M8 upgrade #2 ($1800) will be to take out the new shutter they put in upgrade #1 ($1800) Link to post Share on other sites More sharing options...
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