# Shutter Mechanism...



## weltweit (Oct 31, 2012)

I know there are two curtains and that at slow shutterspeeds there is a time when the whole of the imaging chip is exposed, for example flash synch speed where also the whole chip has to be exposed when the flash fires.

And I know that at higher speeds the opening and closing curtains move across the chip leaving only a small gap between them for a fast exposure. But this means that while any point of the chip may have only been exposed for 1/2000 of a second, the total time of the exposure may have been 1/1000 of a second and in that this *can* lead to distortion in moving images.

I have owned a digital camera that had only an electronic shutter. The lack of a mechanical shutter mechanism, and the lack of a mirror meant it had burst speeds of about 10 frames per second. It strikes me that you could have a shutterless dslr with a mirror but an electronic shutter, though why you might want such an animal I am not yet sure of.

I assume that the mechanical shutter can fire both ways, downwards and upwards as I have never heard mine recocking itself after a shot.

But I don't know, what powers the shutter mechanism, is it spring loaded, is it somehow electrically powered, are there different ways to power a shutter? do they work as they always did in film days? How did they work in film days?

etc etc .. a thread about shutters..


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## weltweit (Oct 31, 2012)

Hmm, bit of google browsing

Mechanical Camera Shutter Type which have moving parts come in two kinds - Leaf and Focal Plane Camera Shutter Types.

The focal plane shutter is found in all digital SLRs.


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## weltweit (Oct 31, 2012)

Interesting video, but he does not say how the dSLR shutter is powered.


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## FridgeMagnet (Oct 31, 2012)

I'm not sure whether you are confusing "electronic shutter" with not really using a shutter to control exposure at all. Lots of film SLRs have electronic shutters, it just means that the mechanism is electronically timed and controlled. On the other hand some digitals in some modes just sample the sensor at/for a specific time rather than for as long as a shutter allows light to fall on it.

Some purely mechanical systems can have very fast frame rates of course, otherwise we would never have had movie cameras.


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## weltweit (Oct 31, 2012)

FridgeMagnet said:


> I'm not sure whether you are confusing "electronic shutter" with not really using a shutter to control exposure at all.


 
Perhaps my wording was not clear, what I meant was cameras like my first, a mirrorless camera with an EVF and back screen on which you could see "what the sensor was seeing" to compose your images. On that I don't think there was a physical shutter of any kind, (not at the focal plane or in the lens) the camera just sampled the data from the chip at whatever speed was set. Perhaps as a result it had burst speeds of about 10fps.



FridgeMagnet said:


> Lots of film SLRs have electronic shutters, it just means that the mechanism is electronically timed and controlled. On the other hand some digitals in some modes just sample the sensor at/for a specific time rather than for as long as a shutter allows light to fall on it.
> 
> Some purely mechanical systems can have very fast frame rates of course, otherwise we would never have had movie cameras.


 
Ok, but they have a physical shutter mechanism which blocks the light from the chip/film. What powers that shutter? are there electrical motors or is there a spring? do they fire downwards then upwards on the next release? or do they recock somehow?

I take the point about movie cams, good point indeed.


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## weltweit (Nov 2, 2012)

Was chatting to some photogs last night and someone mentioned that it could be a couple of solenoids that drive the shutter, apart from that stepper motors could be what drives the shutter. Whatever it is they have to be both fast and precise.


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## Hocus Eye. (Nov 2, 2012)

FridgeMagnet said:


> I'm not sure whether you are confusing "electronic shutter" with not really using a shutter to control exposure at all. Lots of film SLRs have electronic shutters, it just means that the mechanism is electronically timed and controlled. On the other hand some digitals in some modes just sample the sensor at/for a specific time rather than for as long as a shutter allows light to fall on it.
> 
> Some purely mechanical systems can have very fast frame rates of course, otherwise we would never have had movie cameras.


The normal frame rate for movies is 24 frames a second. That is not particularly fast in still camera terms.

With digital cameras there need not be a shutter. The sensor image output can be sent continuously to the viewing screen while only being switched to the SD card buffer for a split second during the "exposure" timed electronically according to the "shutter setting."


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## weltweit (Nov 2, 2012)

I wonder if the shutter always fires downwards, and if it does, when does it recock itself. Possibly as the mirror comes down the two shutter curtains rewind up to their starting position. Otherwise perhaps the shutter fires downward one time and stays down then firing upwards on the next shot.

My understanding is that the shutter fires downwards rather than as it started out firing across the film, because the distance shooting downwards is less than sideways so faster shutter speeds are possible going down than across.


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## weltweit (Nov 4, 2012)

I am told that, since the Nikon F5, shutters have been driven by stepper motors. Presumably quite small ones as the shutter curtains are pretty tiny and very light.

No news yet on whether they recock and always fire downwards.


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## FridgeMagnet (Nov 4, 2012)

Hocus Eye. said:


> The normal frame rate for movies is 24 frames a second. That is not particularly fast in still camera terms.


It's pretty fast in still camera terms! I think the fastest production film SLR was 10fps in continuous mode; not sure what the fastest digital is.


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## weltweit (Nov 4, 2012)

FridgeMagnet said:


> It's pretty fast in still camera terms! I think the fastest production film SLR was 10fps in continuous mode; not sure what the fastest digital is.


 
Well my last mirrorless could do 10fps, but I think what Hocus Eye meant was max shutterspeed of a dslr compared with a shutterspeed of 24/sec for films.


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## Stanley Edwards (Nov 4, 2012)

FridgeMagnet said:


> It's pretty fast in still camera terms! I think the fastest production film SLR was 10fps in continuous mode; not sure what the fastest digital is.


 
Much the same. Top end digital cameras only capture at 9, or 10 FPS in full jpeg.

However, continuous video capture doesn't rely on a shutter.


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## Stanley Edwards (Nov 4, 2012)

weltweit said:


> Well my last mirrorless could do 10fps, but I think what Hocus Eye meant was max shutterspeed of a dslr compared with a shutterspeed of 24/sec for films.


 
Most digital cameras today will allow HD video capture at 24 FPS. Even pocket stuff.


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## weltweit (Nov 4, 2012)

Stanley Edwards said:


> Most digital cameras today will allow HD video capture at 24 FPS. Even pocket stuff.


 
Hi Stanley, but I would guess 24fps is firmly in the no shutter required territory


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## Stanley Edwards (Nov 4, 2012)

weltweit said:


> Hi Stanley, but I would guess 24fps is firmly in the no shutter required territory


 
Yes. But, the sensor doesn't have to record as much information.

Capturing hi-res stills in RAW, or even jpeg requires the sensor to 'be ready' (plus other stuff). A shutter is still necessary to get the best results. Video capture is simply about the sensor recording in 'on' 'off' mode if you like. Even though it is called HD it is actually recording far less information than a 12MP RAW file.

I am still happily using a 1950's Fuji rangefinder. 100% mechanical. The shutter is *spring loaded, and even after 60+ years it seems to be reliable down to 100th of a second. Most modern cameras still use mechanical shutters, but they are electronically regulated. I would guess (don't know) that most digital shutters are electronic.

*when you rewind the shutter blades, or curtain they revert to their start position.


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## weltweit (Nov 4, 2012)

Stanley Edwards said:


> ....
> *when you rewind the shutter blades, or curtain they revert to their start position.


This is an area I am uncertain about. If the shutter is now driven by stepper motors, why would it have to rewind. Why not shoot downwards and stay there and next time shoot upwards and then stay there until the next exposure ... etc etc ..


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## Stanley Edwards (Nov 4, 2012)

Top to bottom always. Don't ask me why.


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## ViolentPanda (Nov 5, 2012)

weltweit said:


> Well my last mirrorless could do 10fps, but I think what Hocus Eye meant was max shutterspeed of a dslr compared with a shutterspeed of 24/sec for films.


 
24 fps is standard filming speed, but if you want to shoot slo-mo, most am-pro cine cameras (regardless of film gauge)  could shoot at 48 and 60 fps too.


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## weltweit (Nov 13, 2012)

My S2 shutter will do from 1/4000 sec to 30seconds to bulb mode. And the lens I have on atm will do from f2.8 to f32 ... I suppose it could be possible to chart the envelope of shutter and iso (fstop also?) into a sort of map of possibilities which would mean you could compare one camera with another.


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## weltweit (Nov 13, 2012)

I suppose it would be a pretty boring graph, a square, unless you could have three axis, but that would be dependent on which lens was fitted so not a true camera to camera comparison.


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## weltweit (Dec 21, 2012)

So, I argued that all modern shutters are driven by stepper motors which are fast and precise. I argued that they do not have springs. However when cleaning imaging chips we fully open the shutter to gain access to the antialiasing filter to clean dust off it. It is argued that you should have fully charged batteries otherwise the shutter could snap shut while you are cleaning the chip, trapping the swab that you are using and damaging the shutter mechanism.

However, if there are no springs, just electric stepper motors, why would the shutter snap closed, surely if the batteries failed the shutter would just stay in its open position, there would not be the power to snap closed. Seems a connundrum.


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## RoyReed (Dec 21, 2012)

Sure looks like springs in the video


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## weltweit (Dec 21, 2012)

RoyReed said:


> Sure looks like springs in the video


 
Hmm. Yes it does. Perhaps they have actuation by spring and return by electric motor?


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## RoyReed (Dec 21, 2012)

IIRC the original electro-mechanical shutters used an electromagnet to hold the shutter closed, but this (obviously) led to serious battery drain, so they quickly changed to exactly what you've said, open by spring power and solonoid to reset. The electronic part of the control I believe is to accurately vary the gap between shutter A and shutter B and keep the exposure constant for any given time value.


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## weltweit (Dec 21, 2012)

RoyReed said:


> IIRC the original electro-mechanical shutters used an electromagnet to hold the shutter closed, but this (obviously) led to serious battery drain, so they quickly changed to exactly what you've said, open by spring power and motor to reset. The electronic part of the control I believe is to accurately vary the gap between shutter A and shutter B and keep the exposure constant for any given time value.


That would also explain why they need to reset. If they were driven both ways by a motor they could fire up and down, but they apparently always reset.


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## RoyReed (Dec 21, 2012)

Also in the old days longer shutter speeds (and B) were fully mechanical, even on electro-mechanical shutters, so taking long exposures didn't drain the battery at all. These days keeping the shutter open for long exposures seems to drain the battery very quickly. I'm not sure how much of that is down to holding the shutter open or keeping the charge on the sensor - I suspect a bit of both.

Edit: Just found some interesting stuff here - http://www.rangefinderforum.com/forums/archive/index.php/t-59646.html

Edit 2: And here a guy strips down a Nikon camera and shutter assembly - http://richard.hornbaker.org/2009/10/10/nikon-d2h-shutter/


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## weltweit (Dec 21, 2012)

RoyReed said:


> ....
> Edit 2: And here a guy strips down a Nikon camera and shutter assembly - http://richard.hornbaker.org/2009/10/10/nikon-d2h-shutter/


After seeing the complexity inside that Nikon, I would have happily paid the $300 odd to have it done professionally


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## weltweit (Dec 22, 2012)

Just thinking out loud.

Assuming a DSLR shutter is actuated by springs and recocked electrically.

The maximum speed a spring can move a shutter across the chip will be dictated by the spring. In fact this will also be the minimum time across the chip as springs always take the same time.

The max flash sync speed will be limited by how fast the first shutter takes (openning) and then (after the shutter is wide open) the second shutter also takes (closing). My dslr has a flash sync speed of 1/125 sec so that suggests one shutter can cross the chip in 1/250 sec closely followed by the other making a total time of 1/125 sec.

For every speed above 1/125 sec the second shutter will start to leave before the first shutter has fully openned. My dslr will go up to 1/4000 sec, I should be able to calculate the gap between the two shutters when openning at 1/4000 sec ..


eta: but if the shutter is recocked electrically compressing the two springs, the two springs must be compressed when the camera is in walk about pre shot mode, which is basically most of the time. If electricity is required to keep the two springs (shutters) cocked, then that would drain the battery more than double the rate of a long bulb exposure.


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