Why are shutters on digital cameras?

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?

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.

OdiN1701 wrote in post #8959317
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.

DaveSt wrote in post #8959353
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!

DaveSt wrote in post #8959353
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.

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

krb wrote in post #8960946
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.

DaveSt wrote in post #8961015
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.

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.

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

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

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.

iAMB wrote in post #8961003
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...

NPuter wrote in post #8962822
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

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.