Why do DSLRs have mechanical shutters?

[spigot]

I almost put this in 'Cameras' but I'm really looking for a solid state answer, so I hope it's appropriate here.

But basically, why do DSLRs have mechanical shutters? Why not just electrically gate the CCD? A few things I've read seem to suggest that upper end DSLRs do just that for very high shutter speeds. But then I came across this. I don't know how valid that article is, but it suggests that even the D40 does some electrical gating at certain shutter speeds, which is why its flash sync speed is higher than that of the D60.

If that article is true, then Nikon felt it was more advantageous to eliminate the gating and change shutters at the expense of flash sync for the D60.

At first I thought it would somehow be related to noise, since a lot of CCD issues are noise related, but with a focal plane shutter, every pixel is exposed for the same amount of time. You could just gate to the exact shutter speed you want and do the whole sensor at once. This would actually even help eliminate the geometric distortion due to the focal plane. Are they concerned about the gate not being sufficient at very high light intensities perhaps? Or can they not gate the CCD until the image is read from it? That doesn't seem to make sense based on point and shoot cameras, which typically utilize an electronic shutter.

 

[NeoPTLD]

Many P&S cameras utilize a combination electronic/mechanical shutter. A few exceptions. Cell phone cameras typically don't have a mechanical shutter.

 

[sxr7171]

Really good question, I hope someone can give a good answer.

 

[SunSamurai]

I would say a digital photography hardware forum would give you better answers than anandtech. Try www.dpreview.com

 

[Modelworks]

A lot of it has to do with the time it takes for a sensor to adapt to changes in light levels. Most CCD are great at going from total dark to light but take longer to go from bright light to less light. If they exposed the sensor to light all the time then there is a chance that in those scenes with bright lighting pictures could have a slight motion blurring in the areas where light was the brightest before.

As CCD improves they will get rid of the shutter.

 

[GodlessAstronomer]

Edit - misread the question. nvm.

 

[ll350]

I'm not even remotely close to an expert on this, but I was under the impression that it was because the picture taken need to be exactly what the photographer saw in their view finder, so the image was mechanically redirected via a mirror to the sensor when they click the shutter.

 

[randay]

Originally posted by: ll350
I'm not even remotely close to an expert on this, but I was under the impression that it was because the picture taken need to be exactly what the photographer saw in their view finder, so the image was mechanically redirected via a mirror to the sensor when they click the shutter.

yes, this is why. they will never get rid of the mechanical shutter in an SLR camera. its the whole point of the thing.

from wiki: The single-lens reflex (SLR) camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to non-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.

 

[PurdueRy]

I'm not precisely sure but my guess would be the processing time it takes to get the information off the sensor. If the sensor is constantly exposed to light the individual charge on each pixel will continue to build as each line of data is scanned and processed. Mechanically preventing light from hitting the shutter allows all the data to be taken off the sensor at the same exposure.

This answer could easily be wrong if it takes next to no time to scan the lines of a sensor. However, given that exposure times can be as short as 1/8000 of a second I would think this could actually make a big difference.

 

[PurdueRy]

Originally posted by: randay

Originally posted by: ll350
I'm not even remotely close to an expert on this, but I was under the impression that it was because the picture taken need to be exactly what the photographer saw in their view finder, so the image was mechanically redirected via a mirror to the sensor when they click the shutter.

yes, this is why. they will never get rid of the mechanical shutter in an SLR camera. its the whole point of the thing.

from wiki: The single-lens reflex (SLR) camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to non-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.

A mechanical shutter has nothing to do with what you see in the viewfinder. You could remove the shutter and you would see the exact same scene through it.

 

[randay]

Originally posted by: PurdueRy

Originally posted by: randay

Originally posted by: ll350
I'm not even remotely close to an expert on this, but I was under the impression that it was because the picture taken need to be exactly what the photographer saw in their view finder, so the image was mechanically redirected via a mirror to the sensor when they click the shutter.

yes, this is why. they will never get rid of the mechanical shutter in an SLR camera. its the whole point of the thing.

from wiki: The single-lens reflex (SLR) camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to non-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.

A mechanical shutter has nothing to do with what you see in the viewfinder. You could remove the shutter and you would see the exact same scene through it.

explain how youll then divert the light from the viewfinder to the ccd.

 

[PurdueRy]

Originally posted by: randay

Originally posted by: PurdueRy

Originally posted by: randay

Originally posted by: ll350
I'm not even remotely close to an expert on this, but I was under the impression that it was because the picture taken need to be exactly what the photographer saw in their view finder, so the image was mechanically redirected via a mirror to the sensor when they click the shutter.

yes, this is why. they will never get rid of the mechanical shutter in an SLR camera. its the whole point of the thing.

from wiki: The single-lens reflex (SLR) camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to non-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.

A mechanical shutter has nothing to do with what you see in the viewfinder. You could remove the shutter and you would see the exact same scene through it.

explain how youll then divert the light from the viewfinder to the ccd.

A mirror? Unless you think that the mirror is the shutter which it is not. The shutter is behind the mirror and closes when you change a lens typically.

http://dslrsherpa.com/wp-conte...ploads/2008/08/slr.jpg

 

[Biftheunderstudy]

Take a look at the Panasonic G1. Its a SLR sized sensor without the SLR, it uses an electronic viewfinder which uses the main and only sensor. What you see in the viewfinder is what is recorded. Though I think it still uses a shutter -- could be wrong on this, cameras aren't really my thing.

 

[randay]

Originally posted by: PurdueRy

Originally posted by: randay

Originally posted by: PurdueRy

Originally posted by: randay

Originally posted by: ll350
I'm not even remotely close to an expert on this, but I was under the impression that it was because the picture taken need to be exactly what the photographer saw in their view finder, so the image was mechanically redirected via a mirror to the sensor when they click the shutter.

yes, this is why. they will never get rid of the mechanical shutter in an SLR camera. its the whole point of the thing.

from wiki: The single-lens reflex (SLR) camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging system, as opposed to non-SLR cameras where the view through the viewfinder could be significantly different from what was captured on film.

A mechanical shutter has nothing to do with what you see in the viewfinder. You could remove the shutter and you would see the exact same scene through it.

explain how youll then divert the light from the viewfinder to the ccd.

A mirror? Unless you think that the mirror is the shutter which it is not. The shutter is behind the mirror and closes when you change a lens typically.

http://dslrsherpa.com/wp-conte...ploads/2008/08/slr.jpg

oh yeah, thats what i thought. didnt know there is another thing right on top of the sensor. makes sense though /palmface.

 

[NeoPTLD]

The optical viewfinder part of the DSLR is exactly the same as a film SLR and the shutter has nothing to do with it. The mirror provides the user with the real optical finder view sought after by some users. Some DSLRs provide the option of using the sensor so you can use the LCD for focusing and framing.

The micro-four thirds design goes back to normal point and shoot style. No optical view finder and view through LCD only, allowing a smaller design.

Almost all digital cameras are more or less an "SLR" though, because the image you're viewing on the LCD and what the camera will capture comes through a single lens. Parallax does not exist.

 

[deputc26]

It's true, the mechanical shutter is a relic from a past era. As are the optics required for single lens reflex (pentprisms, pentamirrors etc.I know I will get flamed for this but it is true). The reasons I have heard for it are primarily to do with sensor life as prolonged exposure to direct light may degrade the sensor over time. This is a valid point. Casio's Exilim EX-F1 uses an electric shutter and as such boasts some incredible multiburst/highspeed video features.

 

[cheesehead]

Originally posted by: deputc26
It's true, the mechanical shutter is a relic from a past era. As are the optics required for single lens reflex (pentprisms, pentamirrors etc.

I'm not so sure about that.

Many photographers hate having to take pictures using a little screen as a viewfinder, and I don't blame them - the screens are small, the color depth sucks, the resolution is terrible, and they wash out in bright sun. Even if you use a tiny LCD as a viewfinder, it's extremely difficult to get more than 1024x768 pixels out of something that will fit in a camera, and even then getting exact color matching is difficult.

A good set of optics, on the other hand, have none of these problems. Effectively infinite resolution with no color distortion.

 

[deputc26]

It is a bit of an exaggeration but the fact remains that the ONLY reason the Single lens reflex optics exist is so that the photographer can see Exactly what the camera sees. Because digital sensors can output that data to an EVF there is no longer a need for an SLR system. The points you brought up about dynamic range, color distortion and resolution have pretty much been invalidated by Panasonics G1. Check this out for the opinions of the webs number one camera nerds. Having the highlights blow out is actually useful as it reflects what the actual picture will look like. There are actually many advantages to the EVF, some of which are mentioned in the above review, most have to do with the camera more acurately displaying what the actual picture will look like (I.e. when effects are added in shot).

 

[Sushifiend3000]

Interesting discussion. Some thoughts from a professional photographer.

explain how youll then divert the light from the viewfinder to the ccd.

Just to clarify: in an slr camera, light is not *diverted* to the ccd. During composition, light from the lens is diverted via the mirror and pentaprism to the viewfinder. When the exposure is made, the mirror is raised out of the light path, the shutter is opened, and the sensor is exposed directly by light passing through the lens.

Almost all digital cameras are more or less an "SLR" though, because the image you're viewing on the LCD and what the camera will capture comes through a single lens.

Well, if there's no mirror then it's missing the reflex part, though I don't know why it's called a reflex (reflects?) mirror.

Regarding live view, for pros, one problem is the video lag. It's minimal, but it's there. If timing is critical it can be very disorienting, and I'm not even talking about sports. Red carpet shooters, who must wait until the subject makes perhaps half a second of eye contact to get their money shot, cannot rely on live view.

Also, in this situation there may be multiple strobes illuminating the scene simultaneously. The lcd cannot recover from this overload quickly enough.

Regarding the mechanical shutter, besides protecting the sensor when closed, it just feels good. I believe Canon and Nikon and maybe others have made a conscious effort to preserve the feel of the mechanical shutter. We like to feel with our hands that our equipment is working, and in fast-paced situations, we can rely on its rhythm to guide our anticipation of events. I can say for myself that the fraction of a second of shutter activity is taken into consideration in critical situations.

The image fidelity of the lcd screen is kind of a non-issue, unless it really sucks, then all you can feel is the machine between you and the scene. For the most part, professional photographer's don't assess lighting and color through the viewfinder. If I'm not running and gunning, I don't even raise the camera to my eye until everything looks right. I do like the 100% field of view of the Panasonic: supposedly you're seeing exactly what will be recorded in the image from edge to edge? This is somewhat rare, and a feature that legends like Alex Webb absolutely rely on for compositional accuracy.

It is a bit of an exaggeration but the fact remains that the ONLY reason the Single lens reflex optics exist is so that the photographer can see Exactly what the camera sees. Because digital sensors can output that data to an EVF there is no longer a need for an SLR system.

I think I revised my response to this comment about ten times. Ultimately my conclusion is that you're probably right. The slr may eventually go the way of film, around the same time they stop making hammers and screwdrivers.

Jerome

 

[deputc26]

Originally posted by: Sushifiend3000
I do like the 100% field of view of the Panasonic: supposedly you're seeing exactly what will be recorded in the image from edge to edge?

This actually will be the case for all nice digicams as it is so easy to implement.

Good points, perhaps you're right and the SLR system will endure, but I think it will die a very slow death. The screen response lag is an issue, a small issue but still an issue with EVFs. There are a number of other small advantages and disadvantages as well.