Why are shutters on digital cameras?

[Ankh3309]

Silly question from a novice user, I was wondering why digital cameras, particularly high-end digital SLR's, have mechanical shutters? I imagine the sensor is electronic, so why can't it be told to simply sample the light for the length of time specified by the shutter speed? Why can't the sensor just start accumulating light when it needs to and stop at the end of the exposure?

[OdiN1701]

It probably can't be switched on and off that fast. Even though it is electronic. The sensor itself probably is just "on" all the time rather than trying to power it up and down. Also that may wear the sensor out more - and a mechanical shutter has been around a long time so they are very good at designing them these days. The shutter is probably also less expensive to replace.

[DaveSt]

It probably can't be switched on and off that fast. Even though it is electronic.

I'm pretty sure they can, and this is pretty much how P&S cameras work as far as I know because they don't have mechanical shutters. As far as I know one big benefit of a SLR over a P&S is that the mechanical shutter has much less lag than a pure electronic solution.

[20droger]

I'm pretty sure they can, and this is pretty much how P&S cameras work as far as I know because they don't have mechanical shutters. As far as I know one big benefit of a SLR over a P&S is that the mechanical shutter has much less lag than a pure electronic solution.
Yes, but note the size of the sensors on P&S cameras.

Everything in life is a compromise. If it weren't I'd be rich AND good looking!

[krb]

I'm pretty sure they can, and this is pretty much how P&S cameras work as far as I know because they don't have mechanical shutters. As far as I know one big benefit of a SLR over a P&S is that the mechanical shutter has much less lag than a pure electronic solution.
P&S cameras do not use the same type of sensors as SLRs. The answers that have been given to this question in the past are that CMOS sensors cannot end the exposure with enough precision for this purpose.

[iAMB]

The whole point of a SLR is to view the image as the lens and sensor would see it. It uses a mirror to project the light than comes through the lens up into your eye. When you press the shutter button, the mirror comes up and directs the light into the sensor. It is a giant breakthrough compared to double-reflect lens cameras where you viewed the image through a separate lens than what the sensor would be seeing. Also it was a mirrored image and difficult for a non experienced users.


Also, is the sensor was left exposed to direct sunlight all the time, the sensor would become fried and would be damaged. If you don believe me and want a cheap example, take a fresh roll of film and expose the film to the sun for a bit. After you do that, try taking a picture with that film and see what develops

[DaveSt]

P&S cameras do not use the same type of sensors as SLRs. The answers that have been given to this question in the past are that CMOS sensors cannot end the exposure with enough precision for this purpose.

That is interesting. I was aware the sensors were different technology but not the details. I always assumed that the sensor in a digital SLR "acts" more like film than the sensor in a P&S camera. I would assume that the sensor in a digital SLR probably collects light as long as it is exposed.

[krb]

I would assume that the sensor in a digital SLR probably collects light as long as it is exposed.
It does, that's why it needs a physical shutter. To make one that doesn't use a physical shutter you need a sensor that can be told to start and stop recording with a greater amount of precision than is offered by the current sensor technology.

[golfecho]

I think what you are describing is exactly what occurs with the "video mode". Shutter is locked up and out of the way (which is why you can't use the viewfinder), and the sensor is used to "capture" one frame after another.

[krb]

The difference being that video doesn't capture frames at 1/8000 of a second.

[DAMphyne]

P&S cams "Don't have a shutter"?
I figured they had a leaf shutter built into the lens.
Hmmm.

[20droger]

Some of the early ones did. Nowadays, virtually all of them have gated sensors because it is cheaper.

The trouble with using gated sensors as shutters is complex. In a nutshell, the larger the sensor, the less reliable the gating.

An example of why DSLRs use mechanical shutters can be seen with the Sigma DP-1, a p&s with a large (APS-C) 20.7×13.8 mm sensor and a fully electron shutter (gated sensor). The maximum shutter speed varies with aperture from 1/1000 sec at f/4 to 1/2000 sec at f/11.

As I've said, everything is a compromise.

[NPuter]

The whole point of a SLR is to view the image as the lens and sensor would see it. It uses a mirror to project the light than comes through the lens up into your eye. When you press the shutter button, the mirror comes up and directs the light into the sensor. It is a giant breakthrough compared to double-reflect lens cameras where you viewed the image through a separate lens than what the sensor would be seeing. Also it was a mirrored image and difficult for a non experienced users.


Also, is the sensor was left exposed to direct sunlight all the time, the sensor would become fried and would be damaged. If you don believe me and want a cheap example, take a fresh roll of film and expose the film to the sun for a bit. After you do that, try taking a picture with that film and see what develops
The mirror is not the shutter...

After the mirror flips up, there is a shutter on the sensor that then opens, exposing the sensor fro the set amount of time...

[iAMB]

The mirror is not the shutter...

After the mirror flips up, there is a shutter on the sensor that then opens, exposing the sensor fro the set amount of time...

Ahh i did not completely understand the Original Post...looking at it now I understand what he is asking. I thought he was referring to the mirror. Whoops my bad :oops:

[whuband]

The OP asks an interesting question. Electronic switching is far faster and more reliable than mechanical switching and is also silent. Switching a sensor off and on seems like a great idea. Sounds like a billion dollar patent to me. I haven't had a quiet camera since my old Leicas, which I wish I still had. Maybe it's the old "that's the way it's always been done" thing with cameras that prevents R & D in this area.

[krb]

The OP asks an interesting question. Electronic switching is far faster and more reliable than mechanical switching and is also silent. Switching a sensor off and on seems like a great idea. Sounds like a billion dollar patent to me. I haven't had a quiet camera since my old Leicas, which I wish I still had.
As has already been stated, current technology does not allow electronic switching to occur with the speed and precision necessary.

Maybe it's the old "that's the way it's always been done" thing with cameras that prevents R & D in this area.
Or perhaps it the old "I've never heard of it so I'll just assume that nobody else has ever thought of this before" thing. You can be sure that Canon, Sony and all the other companies that develop image sensors have been working on this for some time. In fact, they probably already have it working but are still trying to figure out how to make them cheap enough to manufacture.

When they do get this working though it will be great. Not only will it be more quiet but it will allow the shutter speed to be varied over different areas of the sensor. The would be like having a built in graduated neutral density filter, darkening the bright sky and allowing a longer exposure on the darker ground areas.

[number six]

I haven't had a quiet camera since my old Leicas, which I wish I still had. Maybe it's the old "that's the way it's always been done" thing with cameras that prevents R & D in this area.

It's not the shutter you hear in your DSLR, it's the mirror. I guess those with Live View can compare mirror slap and shutter noise, but with my 30D all I can hear is the mirror.

-js

[20droger]

As krb said, there is much research going on in this area.

Yes, there are very fast CMOS switches out there, but they are not photoconductive. Those that are photconductive are not fast switches.

Some day, yes. All cameras will have fully electronic (and silent) shutters. And SLRs will be made with liquid crystal mirrors that never have to move, but rather switch from "silvered" to transparent.

But not yet.

[Lani Kai]

P&S cams "Don't have a shutter"?
I figured they had a leaf shutter built into the lens.
Hmmm.
Nope, they don't.

I'm actually kind of annoyed that while my E-P1 has a mechanical shutter, the shutter is open except directly before and after an exposure. Obviously, this is necessary for live view, but when the camera is off, I want the shutter to close to block off dust when I'm changing lenses.

[whuband]

As has already been stated, current technology does not allow electronic switching to occur with the speed and precision necessary.


Or perhaps it the old "I've never heard of it so I'll just assume that nobody else has ever thought of this before" thing. You can be sure that Canon, Sony and all the other companies that develop image sensors have been working on this for some time. In fact, they probably already have it working but are still trying to figure out how to make them cheap enough to manufacture.

When they do get this working though it will be great. Not only will it be more quiet but it will allow the shutter speed to be varied over different areas of the sensor. The would be like having a built in graduated neutral density filter, darkening the bright sky and allowing a longer exposure on the darker ground areas.

I agree. You made my point. When it's developed, it will be a billion dollar patent. Electronic is far superior to mechanical, or we would still be shooting with cameras from the 1970's.

[beavo451]

The Nikon D70 and D50 dSLR series used a combination electronic and mechanicla shutter. Shutter speeds slower than 1/500 were controlled by the mechanical shutter. Speeds from 1/500 - 1/8000 were controlled by the sensor. The shutter would open, the sensor would turn on and off for the selected shutter speed. This was pretty cool because you could sync *full* power flash at high shutter speeds.

The only problem that I am aware of with these shutters is blooming. When you shot straight into a bright light source (the sun or something) at high shutter speeds, there was a chance that vertical white lines would appear. These lines would be straight up and down starting from the light source. The blooming would only appear at the shutter speeds that were electronically controlled.

[20droger]

The Nikon D70 and D50 dSLR series used a combination electronic and mechanicla shutter. Shutter speeds slower than 1/500 were controlled by the mechanical shutter. Speeds from 1/500 - 1/8000 were controlled by the sensor. The shutter would open, the sensor would turn on and off for the selected shutter speed. This was pretty cool because you could sync *full* power flash at high shutter speeds.

The only problem that I am aware of with these shutters is blooming. When you shot straight into a bright light source (the sun or something) at high shutter speeds, there was a chance that vertical white lines would appear. These lines would be straight up and down starting from the light source. The blooming would only appear at the shutter speeds that were electronically controlled.
That's not a fault. That's a Nikon "feature"!

[mike_d]

It's not the shutter you hear in your DSLR, it's the mirror. I guess those with Live View can compare mirror slap and shutter noise, but with my 30D all I can hear is the mirror.

-js

The mirror is definitely the louder of the two but if you use the mirror lockup function to separate the two movements, you'll hear the shutter does make noise.

[krb]

The Nikon D70 and D50 dSLR series used a combination electronic and mechanicla shutter. Shutter speeds slower than 1/500 were controlled by the mechanical shutter. Speeds from 1/500 - 1/8000 were controlled by the sensor. The shutter would open, the sensor would turn on and off for the selected shutter speed. This was pretty cool because you could sync *full* power flash at high shutter speeds.

The only problem that I am aware of with these shutters is blooming. When you shot straight into a bright light source (the sun or something) at high shutter speeds, there was a chance that vertical white lines would appear. These lines would be straight up and down starting from the light source. The blooming would only appear at the shutter speeds that were electronically controlled.
They were able to do an electronic shutter on these cameras because the cameras use CCD rather than CMOS sensors. On the plus side you get the electronic shutter and higher flash synch speeds. On the down side you get the noise and image quality of a CCD.

[number six]

The mirror is definitely the louder of the two but if you use the mirror lockup function to separate the two movements, you'll hear the shutter does make noise.

How can you hear the shutter? Mirror lockup raises the mirror early, but the mirror drops immediately after it's closed, masking any shutter noise.

I sure can't separate shutter noise and mirror-drop noise in my 30D. But those with live view should be able to...

-js

-js

[mike_d]

How can you hear the shutter? Mirror lockup raises the mirror early, but the mirror drops immediately after it's closed, masking any shutter noise.

I sure can't separate shutter noise and mirror-drop noise in my 30D. But those with live view should be able to...

-js

-js

Enable mirror lockup and set your shutter for 1 second.

Push the shutter button and THUNK, you hear the mirror raise

Push the shutter a second time and, TICK, you hear the shutter open.

At the end of the exposure, the shutter closing sound is masked by the mirror dropping.

[number six]

There ya go! I wasn't thinking very hard, was I?

My shutter (opening) is about half as loud as the mirror drop.

-js