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Thread: How works the shutter of the digital cameras?

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    Panama Hat & Camera's Avatar
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    How works the shutter of the digital cameras?

    How works the shutter of the digital cameras? In film cameras, there were a curtain that opened quickly exposing the film to light.

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    Re: How works the shutter of the digital cameras?

    http://www.steves-digicams.com/knowl...-shutters.html

    Interline Transfer

    Cameras, typically smaller point-and-shoot cameras, that use no mechanical shutters typically use an interline transfer sensor. An interline transfer sensor dedicates a portion of each pixel to store the charge for that pixel. The added electronics necessary to be able to store the charge for each pixel reduces the fill factor of the pixel, in turn reducing it's ability to capture light since a portion of each pixel is not light sensitive. Microlenses can be used to compensate but they are not 100% efficient and they can add expense to the design. Interline transfer sensor's typically have higher noise levels and lower sensitivity than the full frame sensor's used in high end digital SLR's. One obvious benefit is that this design eliminates the need for a potentially bulky mechanical shutter and can turn a purse size camera into a shirt pocket camera.

    Full Frame

    Digital cameras that use a mechanical shutter typically use a type of sensor called a full frame sensor. Unlike the interline transfer sensor (above), the full frame sensor has no circuitry on the pixel to store the charge that builds up as light contacts the array. Cameras that use a mechanical shutter typically bleed off any residual electrical charge while the shutter is closed, open the shutter, and then close the shutter. Once the mechanical shutter is closed, circuitry is then used to shift the charge from each pixel into a storage area. Since the pixels on the sensor remain "live" during readout, if the shutter remained open, light would continue to alter the charge accumulated by each pixel during the shifting operation which could result in blur or ghosting.

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    William W's Avatar
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    Re: How works the shutter of the digital cameras?

    The Digital Single Lens Reflex Camera (DSLR) maintains similar Curtain Mechanisms to those which are used in the later model Film Single Lens Reflex Camera (SLR).

    ***

    Tit bits:

    Not all film cameras had Curtain Shutters.
    Leaf Shutters were reasonably common, in particular cameras/ lenses.

    “Full Frame Sensor” is a now generally accepted, but nonetheless a colloquial phrase, used to describe the sensor SIZE (135 Format 24x36mm).

    Especially, the phrase “Full Frame” is used when describing DSLR cameras to differentiate that sensor size to (usually) an APS-C sized sensor.
    APS-C sized sensors are colloquially known as “Crop Sensors”.

    I would expect that APS-C sized Sensors are in fact more prevalent (by unit of sales) than 135 Format sensor Digital SLRs.

    WW

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    Administrator Manfred M's Avatar
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    Re: How works the shutter of the digital cameras?

    Interchangable lens cameras (for both film and digital) tend to use focal plane shutters, which are the curtain you refer to. There are a couple of practical reasons why this is done; first of all, the closed shutter protects the sensor from contaminants that can enter the camera body when lenes are being changed. The second is related to costs; by putting the shutter in the camera, the manufacturer does not have to build one into each lens. The leaf shutters that Bill mentioned for film cameras were quite common in fixed lens cameras (the shutter actually sits between the lens elements, much like the iris does). Some high-end medium format cameras (Hasselblads, for instance) did this for interchangable lenses as well. This allowed for faster flash synch speeds (in the order 1/500th sec) because of the reduced travel distance and this design also avoided the distortion of fast moving objects parallel to the focal plane at high shutter speeds.

    As Ken pointed out, a mechanical shutter is not really required for electronic sensors, but the design trade-offs do cause image quality issues. Higher end video cameras use this approach and incorporate a turret of internal neutral density fillters to solve these image quality issues.

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    Panama Hat & Camera's Avatar
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    Re: How works the shutter of the digital cameras?

    Ken, Bill and Manfred,
    Thank you for your explanations, but I still have two questions:
    1- DSLR cameras with APS-C sensor has no shutter curtain?
    2- In full frame DSLR cameras with curtain shutter, whence comes the image for the LCD screen?
    Antonio.

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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by Antony View Post
    1- DSLR cameras with APS-C sensor has no shutter curtain? .
    As far as I know all APS-C Format DSLR’s - DO have SHUTTER CURTAINS, i.e. they use ‘Focal Plane Shutters’
    There are TWO Curtains – one leads and the other follows.
    At fast Shutter speeds, it looks like there is a “slit” moving.

    In fact mostly all Format sizes of DSLR have Shutter Curtains, i.e. have ‘Focal Plane Shutters’: but one notable exception is the Hasselblad, which have the shutter mechanisms in their lenses.

    I am not 100% sure of this statement but I think all DSLR’s which do have Focal Plane Shutters, would use Vertical Shutters: that is to say the curtains would move across the SHORTER length of the image rectangle if the camera has a rectangular sensor, (‘Vertical’ being the direction of travel of the Curtains when the camera is held in its ‘normal position’ being LANDSCAPE FRAMING).

    I have read a few references such as “mostly all DSLR’s have Vertical Shutters” – but NOT one of those authors has provided an example where a DSLR has an Horizontal Shutter – (but maybe those authors although not specifically mentioning ‘Hasselblad’, were just referencing Hasselbald NOT using FP shutters at all).

    ***

    Some SLR’s (Film) had HORIZONTAL SHUTTERS - amongst them, Nikon up to about the earlier models of the Nikon “F” Series, and also the Minolta SRT & X Series – my studio used both Nikon and Minolta and the Minolta Film Kit, I still have:

    How works the shutter of the digital cameras?

    ***

    Both Vertical and Horizontal SHUTTER TRAVEL can cause distorted images: most famously is the image of the old race car leaning forward as a result of the image being distorted by a Vertical Focal Plane Shutter.

    ***

    Horizontal Focal Plane Shutters can “squish” or “extended” a moving Subject depending upon the direction of the SUBJECT MOVEMENT in relation to the DIRECTION of TRAVEL of the Shutter.

    ***

    Also, Focal Plane Shutters are a ‘limiting’ factor for what can be the Maximum Flash Sync of a camera.

    (that’s one reason why you pay a lot for a Digital ‘blad, but it is possible though cumbersome to use a Leaf Shutter Lens on other manufacturer’s DSLR - like a Mamiya-Sekor Leaf Shutter Lens on an EOS 5D as an example.)

    If you exceed the Maximum Flash Sync of the Camera -you get this:
    How works the shutter of the digital cameras?

    Also the montage above clearly shows the vertical travel of the shutter curtains.

    (Also as a side note many DSLR cameras have an inbuilt ‘safety feature’ to limit the Shutter Speed maximum to the Flash Sync - so the user CANNOT do as I did above – but you can do it, if you work out how to get around that safety feature.)

    ***

    As these tit bits about Focal Plane Shutters have now touched on the topic of Flash: the Flash can be set to sync with either the FIRST CURTAIN or the SECOND CURTAIN.

    “Second Curtain Sync” means the flash is fired very LATE in the period of the Shutter’s travel. This technique is often used to ‘trail the light behind a moving subject’ and this technique is used (usually) in conjunction with another Flash Technique which is DRAGGING THE SHUTTER.

    "Dragging the Shutter" means using a SLOW enough shutter speed such that the AMBIENT EXPOSURE is about 1 or 2 stops sub-dominate or sometimes about equal to the FLASH EXPOSURE.

    If the flash fires ‘late’ (with second curtain sync) AND you are Dragging the Shutter long enough to capture Subject Movement - the Subject will have a ‘trail’ (i.e. behind them) of movement captured by the AMBIENT EXPOSURE and at the end of that movement the Subject will be frozen by the FLASH EXPOSURE.

    At Social Functions where the Moving Subjects might be holding Sparklers, for example, the effects of using Second Curtain Sync can be quite nice.

    ***

    Quote Originally Posted by Antony View Post
    2- In full frame DSLR cameras with curtain shutter, whence comes the image for the LCD screen?
    If you mean the image immediately AFTER the shot is made – then that is from the camera’s memory. (Some DLSR’s can provide an LCD image momentarily after the shutter is released, without there being a memory card inserted.)

    If you mean the image reviewed after the file is written to the card: then the image is taken from the files contained in the card.

    If you mean the LIVE VIEW image, for all the cameras with which I am familiar – there is a second as the mirror retracts for the sensor to record the live view image.

    WW
    Last edited by William W; 1st August 2012 at 01:16 PM. Reason: Corrected last paragraph - see next two posts for explanation

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    Administrator Manfred M's Avatar
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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by William W View Post
    If you mean the LIVE VIEW image, for all the cameras with which I am familiar - there a second sensor to record the live view image.WW
    Bill - I'm not quite sure about this point. I believe that the way live view works is that that the mirror goes into a locked position and the shutter opens and you are reading data from the actual sensor in your camera. When you press the shutter, the shutter closes and does an actual exposure that is displayed on your camera's rear screen. This is the reason you get that short blackout of the display, while the image is recorded.

    The only DSLRs that don't quite work this way are the Sonys with their semi-silvered mirrors; i.e. no need to go through the mirror locking.

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    William W's Avatar
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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by GrumpyDiver View Post
    I'm not quite sure about this point. (etc) . . .
    First reply- Hmm. ? Will investigate and get back. Thanks.

    ***

    Addition added as an edit:

    ARRRHHH cr@p. MY ERROR, sorry.
    Try this –

    “If you mean the LIVE VIEW image, for all the cameras with which I am familiar – there is a second as the mirror retracts for the sensor to record the live view image.”

    ***
    Aside:

    Explanation: My error was not proof reading my post. I write usually in a word doc. and then cut and paste. I wrote the first two answers about the ‘immediate image’ and the ‘recorded image’, and then I realized “Live View” was also an optional answer. I know I was typing fast, because I was running late and I wanted to put in all that other stuff. I also missed out typing the “is” - but something else went wrong, also: it made quite a mess of the answer didn’t it? I am very annoyed.

    Thanks for picking that up – I will correct the error in the original post and leave this explanation here.

    WW

    PS - Also thanks for the information about the Sony Cameras - I didn't know that.
    Last edited by William W; 1st August 2012 at 01:18 PM.

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    arith's Avatar
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    Re: How works the shutter of the digital cameras?

    I found this interesting; even though I used to dismantle camera's to spot them for instance it was still nice to be reminded about this stuff. Didn't know that live view was using the sensor 100% of the time and so not so good for sun in shot eh.

    Wikipedia has some pictures:

    http://en.wikipedia.org/wiki/Focal-plane_shutter

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    Administrator Manfred M's Avatar
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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by William W View Post
    PS - Also thanks for the information about the Sony Cameras - I didn't know that.
    I'm not sure which models this started with on the Sonys. I remember reading a press release that this was their going forward approach. If you want to solve the problem of "mirror blackout" when you press the shutter, this is certainly an option. 70% of the light goes to the film / sensor and 30% goes to the viewfinder. When it comes to high frame rate in burst mode or trying to record video on a DSLR, the mirror does add technical complexity / limitations, so going with a fixed pellicle addresses some technical issues, while introducing others.

    I remember Canon trying this approch back in the 1960's with the Pellix QL, but I don't remember it being a particularly successful camera. My Leica R3s use a semi-silvered mirror with a secondary hinged mirror to direct light to a metering cell in the bottom of the body, but in that design, most of the light was still directed through the viewfinder and the mirror moved up and out of the way during exposure.

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    Panama Hat & Camera's Avatar
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    Re: How works the shutter of the digital cameras?

    Bill,
    Very many thanks for your explanations. I was meaning the live view image in my second question.
    Antonio.

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    Re: How works the shutter of the digital cameras?

    Manfred,
    Thanks for your explanation. I still do not have a DSLR, I have a super zoom camera and a SLR Olympus OM-2.
    Antonio.

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    Re: How works the shutter of the digital cameras?

    Steve,
    Thank you for your feedback. I searched on internet and found an interesting article on the site [URL="http://www.nikonusa.com/Learn-And-Explore/Nikon-Camera-Technology/ftlzi4ra/1/Live-View-Shooting-Mode.html"].
    Antonio.

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    Re: How works the shutter of the digital cameras?

    The proliferation of the SLR and currently the DSLR means that the leaf shutter is relatively uncommon these days and in professional use found in lens used in LF cameras, and some MF SLRs. But go back in time and the reverse would be true. Not sure if the box brownie camera qualifies as a leaf shutter but Kodak made the Retina and European/English/Japanese makers all had leaf shutters. I normally think of them as Compur shutters. I have a couple in my 'junk' draw

    The compur was a superior type until the invention of the pulsing flash if one was considering syncro-sunlight back when focal plane shutters, horizontal, had sync speeds of 1/30 or 1/20 [Leica].

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    Administrator Manfred M's Avatar
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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by jcuknz View Post
    The compur was a superior type until the invention of the pulsing flash if one was considering syncro-sunlight back when focal plane shutters, horizontal, had sync speeds of 1/30 or 1/20 [Leica].
    Actually my Leicas synch at 1/90, but that is still pretty darn slow. The problem with the Synchro-Compur shutters was that they had to be built into the lens (perferably at a point where the smallest diameter was) and that was not too much of an issue back in the days of fixed lens cameras. Of course putting a shutter mechanism into every lens, like Hasselblad does, drives up the cost, so the focal plane shutter has been the shutter of choice for most interchangable lens cameras.

    The other advantage of the leaf shutter was that they are very quiet. The downside, on the other hand was that they had a maximum shutter speed of 1/500 which was also the flash sych speed..

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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by William W View Post
    As far as I know all APS-C Format DSLR’s - DO have SHUTTER CURTAINS, i.e. they use ‘Focal Plane Shutters’
    There are TWO Curtains – one leads and the other follows.
    At fast Shutter speeds, it looks like there is a “slit” moving.

    I am not 100% sure of this statement but I think all DSLR’s which do have Focal Plane Shutters, would use Vertical Shutters: that is to say the curtains would move across the SHORTER length of the image rectangle if the camera has a rectangular sensor, (‘Vertical’ being the direction of travel of the Curtains when the camera is held in its ‘normal position’ being LANDSCAPE FRAMING).

    I have read a few references such as “mostly all DSLR’s have Vertical Shutters” – but NOT one of those authors has provided an example where a DSLR has an Horizontal Shutter – (but maybe those authors although not specifically mentioning ‘Hasselblad’, were just referencing Hasselbald NOT using FP shutters at all).

    ***

    Some SLR’s (Film) had HORIZONTAL SHUTTERS - amongst them, Nikon up to about the earlier models of the Nikon “F” Series, and also the Minolta SRT & X Series – my studio used both Nikon and Minolta and the Minolta Film Kit, I still have:

    How works the shutter of the digital cameras?

    ***

    Both Vertical and Horizontal SHUTTER TRAVEL can cause distorted images: most famously is the image of the old race car leaning forward as a result of the image being distorted by a Vertical Focal Plane Shutter.

    ***

    Horizontal Focal Plane Shutters can “squish” or “extended” a moving Subject depending upon the direction of the SUBJECT MOVEMENT in relation to the DIRECTION of TRAVEL of the Shutter.

    ***

    WW
    Bill, I believe that the terms 'horizontal' and 'vertical' refer to the orientation of the slit between the shutter curtains, not the direction that the shutter travels. So a 'vertical' shutter would move from one side to the other, along the longest axis of the film frame, while the 'horizontal' shutter would move from bottom to top along the shortest axis of the film frame.

    This does coincide with the distortions you mention: a vertical shutter, moving from one side to the other, would allow a car to appear longer or shorter (depending on the direction it was traveling in) while a horizontal shutter would cause the car to appear tilted as the shutter opening moved from the bottom to the top of the film frame.

    I remember see a horizontal shutter on a Nikon 35mm back in the 1970's; what impressed me most was that the shutter was made of titanium blades, rather than a rubberized cloth curtain.

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    William W's Avatar
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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by John Morton View Post
    Bill, I believe that the terms 'horizontal' and 'vertical' refer to the orientation of the slit between the shutter curtains, not the direction that the shutter travels. So a 'vertical' shutter would move from one side to the other, along the longest axis of the film frame, while the 'horizontal' shutter would move from bottom to top along the shortest axis of the film frame.

    This does coincide with the distortions you mention: a vertical shutter, moving from one side to the other, would allow a car to appear longer or shorter (depending on the direction it was traveling in) while a horizontal shutter would cause the car to appear tilted as the shutter opening moved from the bottom to the top of the film frame.
    I believe my original statement is correct.

    The terminology originally used was “Horizontal run shutter".

    I am in France at the moment but I am quite confident that my authoritative texts in my office in Sydney will support my original post.

    If you have any First Reference Sources which supports the claim that ‘horizontal’ and ‘vertical’ refer to the orientation of the slit and NOT the direction of travel, then could you please post same.

    WW

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    Re: How works the shutter of the digital cameras?

    Vertical shutter run vertically. Horizontal horizontally. The advantage of the vertical is that the distance the leaves of the shutter have to move is shorter so for the same movement speed they allow faster shutter speeds.

    Traditionally they have 2 modes of operation. Shutter open shutter close and both at the same time to traverse a slit across the sensor / film. This can introduces distortion into shots of fast moving objects. The appearance differs according to which direction the shutter moves. This also limits flash sync speed.

    Before going any further this article explains this style of basic shutter operation and refers to each of the 2 moving parts as curtains.

    http://en.wikipedia.org/wiki/Focal-plane_shutter

    Electronic first curtain shutter provide one of the curtains electronically. Normally the 1st curtain on a conventional shutter is the first to move followed by the 2nd curtain. On this type of camera the shutter is closed and the entire sensor is cleared. The electronic ones achieve the same thing by clearing rows of pixels one at a time just ahead of the mechanical 2nd curtain.

    With both set ups the entire frame is read after the 2nd curtain is shut to prevent further light getting onto the pixels just as it is with a mechanical 1st and 2nd curtain. Compacts often had shutters as well. Simple ones to allow light to be blocked when the sensor was read full frame all in one go. They then moved onto a different system where some arrangement of pixels is read and cleared at the same time one after another until an entire frame can be built up. This allows video to be taken with the shutter wide open. The same idea is also used for live view. This is why I mentioned SOME pixel arrangement can be read and cleared at the same time. Sensors often have logic built in that allow them to be read in a number of ways. I don't own one but I understand that Canon live view cameras can be connected to a PC and part frame views displayed with relatively fast update rates. As the pixels on the screen are spaced further apart the view is effectively magnified allowing very precise focusing. Useful on microscopes for instance. In real terms though the pixels may be read in groups and reduced to a single pixel on the screen. A process called binning. Some technical cameras do this even discarding the colour information to achieve faster update rates for focusing.

    Sony once produced a camera that used a part silvered mirror to reflect the image to a separate sensor for live view. Some people at the time thought that this was a sensible way of obtaining live view.

    Quickly looking on the web I found this which is fairly accurate. Here video is mentioned line by line but in real terms all sorts of pixel reading techniques can be used including groups of any shape on the sensor. All depends on the logic built into the chip. Some technical camera chips have a bulb mode and maybe even a flash mode built in.

    http://www.mhohner.de/newsitem2/efcs

    Interesting comment about reduced shake. yes maybe but. Cost is the driving factor.

    Personally I wouldn't be at all surprised if mechanical shutter disappeared entirely at some point. Web cams for instance have never had one and can shoot video and single shots. Compacts don't seem to have one any more either not that I would take an expensive one apart to find out. One day one of mine might break or stop working................

    -

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    Re: How works the shutter of the digital cameras?

    Not meaning in any way to be pedantic, Hasselblad use both shutter mechanisms in fact. The most popular being the "in-the-lens" Compur type, commonly used with the 'C' series bodies, but there was also a focal plane shutter in the 'F' series bodies.

    As it happens, the very first Hasselblad, the 1000F used a focal plane shutter - hence the 'F'

    The CF lens series are usable on both bodies - the shutter on the body is used in preference to the one in the lens.

    With regard to another reply here, Nikon still uses Titanium bladed shutters - and carbon fibre too. It's interesting (to me ) to note that the flash syncronisation is the give away - it's a higher speed, in general, if the shutter runs vertically - it travels less and thus the sync can be a higher speed.

    Electonic flash is so fast that the whole shutter has to be open for the exposure to be even - thus the fastest sync speed corresponds with the fastest speed at which there is no shutter blade in evidence. Any faster and the second (general descending) curtain would cut off part of the picture.

    But I digress...

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    Re: How works the shutter of the digital cameras?

    Quote Originally Posted by darkslide View Post
    Electonic flash is so fast that the whole shutter has to be open for the exposure to be even - thus the fastest sync speed corresponds with the fastest speed at which there is no shutter blade in evidence. Any faster and the second (general descending) curtain would cut off part of the picture.

    But I digress...
    That was the case before HSS technology came on board. Here the flash pulses light quickly so as to act as a continues light source, so the camera can use any shutter speed. I believe you lose around a stop as the multiple flashes approach puts out light at less than maximum power.

    Your statement is quite correct if one uses studio strobes or some of the lower end "dumb" flashes that some of the low cost Asian manufacturers put out.

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