Stupid shutter question

[Anorakus]

I've always wondered... why do DSLRs have a mechanical shutter, whereas compacts control the exposure electronically* ?

(*correct me if I'm wrong about this)

TIA

A.

 

[purpleclouds]

A lot cheaper to manufacture an electrical system these days probably! Also the sensor size doesn't really warrant a mechanical system..it'd be very fiddly and tiny!

 

[CT]

It's been a long time since cameras had fully mechanical (clockwork) shutters, but they are all mechanical in the sense that they have moving parts, however, they're pretty well all electronically controlled nowadays which is how shutters these days are pretty well 'stepless' in the speeds they can use.

This is true of shutter systems in most modern cameras whether compacts or DSLRs.

Where DSLRs (and SLRs) differ is in having a focal plane shutter.

To understand why we have a FP shutter, it's important to understand that prior to the SLR being invented, shutters were either in the lens or just behind it. With the invention of the SLR, the lens also became the viewfinder, so it was imperitive that the shutter be removed from the lens so that it could be open all the time for use as a viewinder.

They put the shutter in the only place they could - right at the back of the camera where it sits almost touching the film/sensor and is to all intents and purposes in the focal plane - hence the name.

We gained a lot of advatages with the SLR:-

Looking through the actual taking lens and seeing the FOV regardless of lens focal length.

Being able to actually see if we're in focus.... on ground glass.

Unfortunately, we also have to put up with the FP shutter which is a big heavy mechanism which self destructs with continued use, and due to the fact that it consists of two curtains, or blinds, it causes us problems synching with flash above certain shutter speeds - a problem we didn't have previously.

 

[chameleon]

Thats an interesting potted history of shutters but it dosent answer the question. I have wondered this myself, why do DSLRs have a shutter when, presumably the sensor could freeze a moment just as well?

 

[CT]

Well I thought I did? The original question was based on the erroneous assumption that compacts control the exposure electronically, while DSLRs have mechanical shutters.

They both have electro mechanical shutters ; mechanical shutters controlled electronically. All cameras have a shutter, there's not been a better arrangement found for keeping the light from the sensor till the moment of exposure.

If you could have a system where light was continually falling on the sensor all the while, with the sensor remaining insensitive to light till the moment of exposure, then you wouldn't need a shutter, just some sort of electronic timer which controlled the sensitive period of the sensor. I'd have thought though that if it were possible they'd have done something similar by now.

I did read somewhere that experiments with liquid crystal shutter blinds ran into problems with the crystal not being opaque enough, so obviously they're trying, and the shutter life and failure rate of FP shutters must be a huge PITA for manufacturers, but until they come up with something better it looks like we're stuck with what we've got.

 

[Finn]

I seem to remember the 40D has a partly electronic shutter? As in the physical bit doesnt close but some clever electricery replaces it (eg the sensor stops collecting photons, or those photons no longer matter or something (I think its the "quiet mode" where the shutter doesnt reset until you release the button)

and I think thats similar to how a point and shoot works. there is no mechanical shutter at all, its a bit like live view mode where its constantly taking the picture when you press the shutter button all it does is go "okay this picture this is the one I want to keep".

I'd assume part of the reason for not having a physical shutter is exactly because of live view, it needs to keep taking pictures for the preview screen so cant have a physical barrier stopping ti from doing so.

 

[Kev M]

If you could have a system where light was continually falling on the sensor all the while, with the sensor remaining insensitive to light till the moment of exposure, then you wouldn't need a shutter, just some sort of electronic timer which controlled the sensitive period of the sensor. I'd have thought though that if it were possible they'd have done something similar by now.

Isn't that what Nikon did with the D70 cameras CT? They can sync flash upto a ridiculous speed providing you trigger is up to it.

 

[CT]

I'm not really up on Nikons these days Kev, but according to DP Review the D70 has a partly mechanical, partly CCD shutter. Maximum flash sync is 1/500th it seems, which is good for a FP shutter (Hi speed sync apart aobviously)

 

[jgs001]

If all camera have some form of mechanical shutter, then I'm puzzled as to the operation of my Z2. The viewfinder/LCD is full through the lens. The LCD is rotated to show in the viewfinder if that's required. Does this mean, that when the shot is being lined up, the shutter is open, the sensor operating to provide the signal to the display, then when the shutter button is pressed, the camera closes the shutter, then opens it to expose, closes and reopens it again ? Or does it just capture that instants data from the sensor and write it out ? (which would explain it's silent operation, now I've turned most of the sound effects off which only serve to slow the camera down).

 

[CT]

I can't find any info on the Z2 shutter John.

 

[jgs001]

ok Thanks CT, was just wondering really. It works, and now my kids are nicking it... I'd better be careful or they'll be having my 450d away from me too

 

[mrgubby]

I don't think compact/P&S/phone cameras have a mechanical shutter, the ccd/sensor is 'sampled' for the shutter time to get the required exposure.

This is why on a lot of them you can switch the 'shutter' sound on & off

 

[CT]

LOL. Just a thought but a lot of bridge SLR type cameras have an electronic viewfinder, rather than the optical one we get in a conventional SLR, i.e. the image is duplicated in the viewfinder digitally (like a video camera screen) which could explain the way your viefinder is working?

 

[Kev M]

How do leaf shutters work in MF slrs then CT?

 

[CT]

How do leaf shutters work in MF slrs then CT?

They're basically a very simple mechanism (compared to a FP shutter) - just a blade which uncovers the open diaphragm in the lens. Because the whole aperture is open throughout the exposure time, regardless of shutter speed there's no limitation on flash sync speed right up to the max speed your shutter allows.

Often the shutter is built into each lens, which is the case with my RB67.


If you want to get your head around how you can actually have a shutter in the lens in a SLR MF camera like the RB67, it's actually quite interesting. In my RB, the shutter works in reverse to normal, in that it remains open during normal viewing, so that the image can be bounced off the mirror up onto the focusing screen. During this period the film is protected from light by a huge baffle in the rear of the camera which covers the film opening in the mag back.

When you take the shot, the mirror and the baffle swing up out of the way and the shot is taken, leaving the shutter closed. When you manually wind on, the baffle and the mirror come down again, and the shutter is reset in the open position, giving you back your image on the focusing screen.

It impresses the ass off me! You need to have a good look at your own MF camera to see exactly how it all works.

 

[Andy FujiS7000]

I don't think compact/P&S/phone cameras have a mechanical shutter, the ccd/sensor is 'sampled' for the shutter time to get the required exposure.

Thats what I thought, didn't think there was any mechanical shutter in anything other than slrs generally speaking. My bridge camera goes down to 1/10000 of a second which seems faster than most slrs, which I put down to the fact its just an electronic sensor sample rather than a mechanical operation.

 

[Kev M]

Cool CT, you da man. Is there a way of testing the shutter accuracy on a camera or not. My first roll of film all came out overexposed so I wondered how much was the bi-ped interface module or if there's a fault with the camera.

 

[Kev M]

Here's a handy (ish) link to sync speeds and how cameras like the D70 sync way past 1/500. Apparently the Canon G7&9s can sync upto 1/2000th too. (and before anyone chimes in we're talking about not using HSS or FP mode here )

strobist

 

[CT]

Any camera repair outfit should be able to check shutter accuracy. It's not really a job you can tackle yourself, although just listening to if there are obvious differences in speeds should give you some idea if all seems well.

You can never rule out user error with a manual camera Kev, and a lot depends on how you were metering. Probably doing your metering with a DSLR and tranferring the settings should get you in the ballpark. I'd worry about getting the shutter checked when you're reasonably happy you've metered accurately and still getting a problem. Springs can weaken in these shutters after years of use.

 

[CT]

Here's a handy (ish) link to sync speeds and how cameras like the D70 sync way past 1/500. Apparently the Canon G7&9s can sync upto 1/2000th too. (and before anyone chimes in we're talking about not using HSS or FP mode here )

strobist

Cool link -I'll have to get my head round that later on. The progress is being made though it seems, and not before time! Shutters have really lagged behind the other huge strides which ave been made in camera technology.

 

[Kev M]

No DSLR on that occasion, was trying not to carry too much. Was using the metered prism but as pointed out previously it's centre weighted not matrix. I think the meter is still way out though.