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04-03-2008, 11:05 AM   #1
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why do we still need shutters

well having graduated into the more elite circle of my "photographic society" with my recent purchase of a K10D and identical pair of lenses that a fellow member got with his new K10D at the same time as me (coincidence) I was invited down to the pub after the meeting to discuss photography in depth

now one member brought up an interesting point: why do we need a shutter on a digital camera ? and do the digicams/bridge cameras and P&S have one at all ?

we discused it a bit and never really came up with a solution to the enigma as it was pointed out there is the option of just turning it on and off to expose the image,

So I ask you what purpose does the shutter serve in a DSLR ? I thought perhaps that by keeping the sensor in the dark it does not get filled with light or something, undoubtedly keeping it off when not required reduces noise due to heating of the sensor but thats a seperate issue.

please help us resolve dilema


Last edited by simons-photography; 04-08-2008 at 02:35 PM.
04-03-2008, 11:20 AM   #2
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Steve's Digicams - Tech Corner - September 2007

There you go. I found this the other day while telling people digital cameras don't have shutters. -- I wasn't correct.

It's an interesting read.
04-03-2008, 11:31 AM   #3
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yes its quite interesting and along the lines of what i suspected
04-03-2008, 11:32 AM   #4
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the saying If it ain't broke don't fix it comes to mind. what I don't get is why does everyone want to strip out everything that makes an SLR and SLR. if you would like an 'electronic shutter' then why not use a P&S? besides a simple mechanical device has proved very reliable for a very long time no need to change it for something that hasn't been proven to be as reliable despite whether its cheaper to manufacture or not. I think one might need to spend more time taking pictures rather than discussing camera parts.

04-03-2008, 11:48 AM   #5
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QuoteOriginally posted by séamuis Quote
the saying If it ain't broke don't fix it comes to mind.
That saying is short for "I don't understand how it works." IMHO. Fortunately not everyone has that attitude or there would be no innovation. An electronic shutter makes lots of sense. It would be quieter, more reliable, induce no camera shake, and be more flexible than its mechanical counterpart. I know that a camera was annouced recently that could shoot 1200fps. Try doing that with a mechanical shutter. I would love to see them come to DSLRs. Just not at the expense of image quality though.
04-03-2008, 11:56 AM   #6
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QuoteOriginally posted by séamuis Quote
the saying If it ain't broke don't fix it comes to mind. what I don't get is why does everyone want to strip out everything that makes an SLR and SLR. if you would like an 'electronic shutter' then why not use a P&S? besides a simple mechanical device has proved very reliable for a very long time no need to change it for something that hasn't been proven to be as reliable despite whether its cheaper to manufacture or not. I think one might need to spend more time taking pictures rather than discussing camera parts.
yikes i wasn't meaning to say we don't need them rather wondering why manufacturers were still using something that they could probaably do without I'm quite in support of the cameras mechanical parts.... I love the chuncky mechanical differences between my old bridge and my new K10D
04-03-2008, 12:04 PM   #7
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QuoteOriginally posted by séamuis Quote
the saying If it ain't broke don't fix it comes to mind. what I don't get is why does everyone want to strip out everything that makes an SLR and SLR. if you would like an 'electronic shutter' then why not use a P&S? besides a simple mechanical device has proved very reliable for a very long time no need to change it for something that hasn't been proven to be as reliable despite whether its cheaper to manufacture or not. I think one might need to spend more time taking pictures rather than discussing camera parts.
I have to disagree with you.
Currently, the mechanical shutter is a HANDICAP to the potential of DSLR. Sure, it ain't broke, but it ain't good enough and the technology isn't there to fix it yet. And why would you equate electronic shutters with P&S??? It is a more advanced technology, not inferior. Just that they have not solved the problems in large sensors.

Imagine with electronic shutters, you can have flash sync up to your maximum shutter speed - 1/4000s or even 1/8000s without the need for high speed sync multi-burst. And you can get much higher FPS (see how K20D can achieve 21 FPS when mechanical shutter is out of the equation).
04-03-2008, 12:13 PM   #8
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QuoteOriginally posted by séamuis Quote
the saying If it ain't broke don't fix it comes to mind. what I don't get is why does everyone want to strip out everything that makes an SLR and SLR. if you would like an 'electronic shutter' then why not use a P&S? besides a simple mechanical device has proved very reliable for a very long time no need to change it for something that hasn't been proven to be as reliable despite whether its cheaper to manufacture or not. I think one might need to spend more time taking pictures rather than discussing camera parts.
then why are you still here? go take pictures..

geeze.

04-03-2008, 12:31 PM   #9
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QuoteOriginally posted by nosnoop Quote
I have to disagree with you.
Currently, the mechanical shutter is a HANDICAP to the potential of DSLR. Sure, it ain't broke, but it ain't good enough and the technology isn't there to fix it yet. And why would you equate electronic shutters with P&S??? It is a more advanced technology, not inferior. Just that they have not solved the problems in large sensors.

Imagine with electronic shutters, you can have flash sync up to your maximum shutter speed - 1/4000s or even 1/8000s without the need for high speed sync multi-burst. And you can get much higher FPS (see how K20D can achieve 21 FPS when mechanical shutter is out of the equation).
amen and hallelujah. (and thanks for saving me the time to write the same thing).

And I just dont understand why no cmos sensors have this capability,most ccd sensors do, the one in the earlier pentax cameras did, they just didnt use it. nikon did.

an electronic shutter is just a way of telling the sensor to stat and stop recording within an interval. now i am pretty sure that the sensor isnt actiely recording all the time the camera is on anway so they already should have the extremely basic capability of turning the damn thing on and off. if they had done it on the k20d it would have a big advantage that even the most expensive canikon bodies cannot do. would sure be popular with the strobist crowd.
04-03-2008, 12:34 PM   #10
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QuoteOriginally posted by Gooshin Quote
then why are you still here? go take pictures..

geeze.
thats not quite what I was getting at. I don't browse the forums to simply discuss camera parts I browse for lots of reasons (when I'm not taking pictures). :ugh:
04-03-2008, 12:38 PM   #11
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QuoteOriginally posted by simons-photography Quote
yikes i wasn't meaning to say we don't need them rather wondering why manufacturers were still using something that they could probaably do without I'm quite in support of the cameras mechanical parts.... I love the chuncky mechanical differences between my old bridge and my new K10D

I wasn't insinuating you said that, if thats how it came across then I apologize.
04-03-2008, 12:42 PM   #12
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QuoteOriginally posted by nosnoop Quote
And why would you equate electronic shutters with P&S??? It is a more advanced technology, not inferior.
I equated it with a P&S because some P&S cameras use this technology, I made no reference to inferior/superior you simply made an assumption.
04-03-2008, 01:25 PM   #13
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QuoteOriginally posted by simons-photography Quote
well having graduated into the more elite circle of my snobby "photographic society" with my recent purchase of a K10D and identical pair of lenses that a fellow member got with his new K10D at the same time as me (coincidence) I was invited down to the pub after the meeting

now one member brought up an interesting point: why do we need a shutter on a digital camera ? and do the digicams/bridge cameras and P&S have one at all ?

we discused it a bit and never really came up with a solution to the enigma as it was pointed out there is the option of just turning it on and off to expose the image,

So I ask you what purpose does the shutter serve in a DSLR ? I thought perhaps that by keeping the sensor in the dark it does not get filled with light or something, undounbtedly keeping it off when not required reduces noise due to heating of the sensor but thats a seperate issue.

please help us resolve dilema
Good question - there are in fact cameras and CCDs that have fully electronic shutters and some that use both!!!

All CCDs can be read out during exposure (hence the video feed to the LCD on digicams and now live view SLRs). However, one problem with electronic shutters on simple CCDs is "smear" or "ghosting" of highlights as photosite charges are shuffled across the sensor during readout as the sensor has to remain switched on to be read. If the exposure time is relatively long (say 1/30) the effect is quite small as the exposure time of the other pixels is minimal, but at faster shutter speeds (1/1000) it can be quite nasty. Its much better to stop the light before readout.

Now there are ways around this. An "electronic shutter" can simultaneously dump the charge from the photodiode into a non-photosensitive "scavenger diode" at a prearranged time simply by changing the polarity of the pins on each sensor row. Readout then takes place from the scavenger diodes so no smear occurs. These devices have the major advantage of requiring no mechanical shutter (lower camera cost and smaller size) and can achieve very high shutter speeds (and flash synch speeds). They are frequently used in phone cameras and video devices.

However the scavenger diode has the same capacity as the photodiode plus there is additional control circuitry at each photosite, so such devices (sometimes called inline transfer CCDs) typically have lower fill factors and well depth than ones without (which are called full frame transfer CCDs).

Whereas the former are widely used in phone cameras and other low end applications, and for high speed video applications, they are unpopular in high resolution dedicated still cameras because of their lower sensitivity and ISO performance. Using a mechanical shutter allows the sensor to have fewer components and more light gathering area, hence better sensitivity.

For video on a digicam it is quite possible to use a FFT CCD as the shutter speed remains quite low and the output is much lower res, and only displayed briefly when viewing, so the ghosting is less noticeable. However decent quality dedicated video cameras use electronic shutters and their sensitivity is less of an issue because they use far lower resolution sensors (with much bigger photosites) and use interline CCDs with high shutter speeds to freeze action on each frame.

So what about CMOS you may ask! Well, they dont show ghosting because its not the full photosite analogue charge thats shuffled along the readout row, only the output digital value from the AD converter.

However CMOS has a different problem: without adding more transistors to each photosite to add clocking synch controls, you cant switch them all "off" simultaneously, so moving objects are strangely distorted across the frame (so a mechanical shutter is still needed). More transistors means a lower fill factor - the main problem with CMOS sensors is crowded photosites (the simplest have 3 transistors - so called 3T sensors) adding more is not a favoured option for high quality devices.

However now that CMOS sensitivity and quality has mostly caught up with CCDs, 4T and 5T designs offer an advantage in very high speed video applications because the data can be read out in parallel across the whole sensor, allowing potentially much higher frame rates or much higher video resolution, or both.

Sorry - bit of an oversimplification but I am sure someone will correct me if I have not got it exactly right.
04-03-2008, 01:26 PM   #14
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I've wondered the same thing. Electronic shutters seem to make much more sense, though I enjoy the "clunk" my shutter makes.
04-03-2008, 01:42 PM   #15
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QuoteOriginally posted by rfortson Quote
I've wondered the same thing. Electronic shutters seem to make much more sense, though I enjoy the "clunk" my shutter makes.
I think more of that is the mirror movement and aperture blades anyways.
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