Silly question (maybe?) Why is a physical shutter needed on a digital camera?

[Kit Lens Jockey]

I've tried to find some definitive answers to this question in the past, but I still don't quite completely understand it. I mean, with film, you had a physical piece of light sensitive material, so obviously you need a physical device to only expose it for a set amount of time. Hence, a shutter...

But digital cameras still use this same clunky, prone to wear shutter. Why? Isn't it possible to just electronically read the light hitting the sensor for whatever length of time you want the "shutter" speed to be, and that would be it? Why does there need to be the same physical device there to regulate it in the same way there is with film?

Looking online, the best info I could find was something along the lines of "Well, a digital sensor kind of stores up light that hits it, so it's not as simple as just reading the light hitting it for a certain amount of time." Makes sense, I guess. Maybe the answer is too technical for anyone not working in optical engineering to understand.

But, it does seem like some cameras do go without the shutter, right? Isn't that what this "global" shutter is that I've read about? So is it just that some sensors are capable of operating without a shutter, while some aren't suited to it?

 

[astroNikon]

You are asking about an Electronic Shutter. Many mirrorless cameras has electronic shutters, and Canons DSLRs do too ==> Differences between electronic and mechanical shutters | Nikon Knowledgebase

more overall into about the current challenges with electronic shutters ==> The Future of the Electronic Shutter | PDN Online

 

[Kit Lens Jockey]

Right, but Canon (and I believe Nikon, right?) still have mechanical shutters as well. Why the need for the mechanical shutter that wears out if the function of it can be electronically reproduced? (Have not had a chance to read the article you linked to yet, perhaps the answer is in there.)

Edit: Ok, yeah, the article spells out some of the difficulties of using an electronic shutter pretty well. Thanks. Sounds like it's only a matter of time until shutters go full electronic for still photos.

 

[astroNikon]

another indirect limited factor is the mirror box in DSLRs. which limits speed but current gives better AutoFocus between shots, great for moving subjects.

They're working on better and better AF through the sensor which will also help compact the camera overall.

 

[robbins.photo]

Right, but Canon (and I believe Nikon, right?) still have mechanical shutters as well. Why the need for the mechanical shutter that wears out if the function of it can be electronically reproduced? (Have not had a chance to read the article you linked to yet, perhaps the answer is in there.)

Edit: Ok, yeah, the article spells out some of the difficulties of using an electronic shutter pretty well. Thanks. Sounds like it's only a matter of time until shutters go full electronic for still photos.

The shutter mechanism also has the mirror mounted on it that reflects what it sees to an optical viewfinder - without that mirror you need to use an electronic view finding system, which have some issues with speed as well as battery life.

 

[Kit Lens Jockey]

Yeah, I know that the mirror still needs to be there to allow the autofocus to work and to give you an optical viewfinder, I just didn't really understand why you couldn't keep the mirror but get rid of the shutter behind it. So basically it would just be like flip up the mirror, read the sensor, and flip down the mirror, without dealing with the shutter.

 

[jcdeboever]

Cameras have a shutter?

 

[Dave442]

I would like to see an electronic shutter that can fully replace the focal plane shutter. I certainly don't expect to see it any time soon on anything I plan to buy. A true global shutter that could give flash sync speeds like a leaf shutter would be a big step and give an edge over the focal plane shutter.

Being electronic the price may start high, but overt time it should drop while the mechanical shutters are probably just going up in price.

 

[table1349]

Think of it this way. A light switch only turns on and off so fast. That is what you are doing with an electronic shutter turning the sensor on and off. With a mechanical shutter you can have a vast array of speeds wherein the sensor is already on and the shutter just moves at the predetermined speed.

 

[astroNikon]

Cameras have a shutter?

Some cameras have a stutter too

 

[petrochemist]

Camera phones & compact cameras often only have electronic shutters. So obviously a mechanical shutter is not needed.
As the posts above have explained mechanical shutters still have advantages, so better cameras still use them. One of my mirrorless bodies has the option to use mechanical or electrical shutter. There are quite a few options that are no longer available with the electronic shutter - presumably for sound engineering reasons!
These include the faster shutter speeds, and several others that are less easy to understand (for example, IIRC flash was unavailable at any shutter speed).
The silent electronic shutter is great, but it's the first thing top change when any option is not available...

 

[beagle100]

Camera phones & compact cameras often only have electronic shutters. So obviously a mechanical shutter is not needed.
As the posts above have explained mechanical shutters still have advantages, so better cameras still use them. One of my mirrorless bodies has the option to use mechanical or electrical shutter. There are quite a few options that are no longer available with the electronic shutter - presumably for sound engineering reasons!
These include the faster shutter speeds, and several others that are less easy to understand (for example, IIRC flash was unavailable at any shutter speed).
The silent electronic shutter is great, but it's the first thing top change when any option is not available...

yes, and the ability to sync with external strobes is important

 

[KmH]

There are image effects that can only be done with a mechanical shutter.
Which is why cameras having a mechanical shutter usually give the photographer the option of having flash sync on either the front(first) or rear(second) shutter curtain.

Don't forget that there are 2 types of electronic shutter - global and rolling.
A rolling type electronic shutter doesn't work very well with moving objects.

 

[Solarflare]

The problem with electronic shutters is that they have a flash sync of like 1/5 to 1/15 sec (*). Thats how long it takes the camera to read the whole sensor at full resolution.

That means flash is basically unuseable, artifical light will cause inconsistent lighting, and MASSIVE rolling shutter effects.

One can see this a bit with video. During video, the camera will read the sensor only with 8 bit precision, which is a lot faster than the usual 12 or 14 bit. However, theres still some rolling shutter visible; specifically the socalled 'Jello' effect which make the whole video go wobbly.

Theres also global shutters. Some older CCD cameras have them (not all of them though).

However, global shutters add NOISE. Thats due to the additional step needed to store the electric charge of the photo diode in some other, not light sensitive place.

The industry is working on getting global shutters which do not add noise. If we ever get them, mechanical shutters are history.

(*) They might be higher, but they are definitely not very high, as one can test with cameras that offer electronic shutters - they have very strong rolling shutter effects.