Why do we have a mechanical shutter?

[sheepie]

OK - I've been mulling this one over for several months now (I think I mentioned it at Birddogs one day earlier in the year), and am now getting around to posting it...

From Nikon Technical Specifications...
http://www.nikonusa.com/template.php?cat=1&grp=2&productNr=25214
Shutter: Combined mechanical and CCD electronic shutter,30 to 1/8000 s in steps of 1/3 or 1/2 EV, bulb

If the mechanical shutter is overiden for the higher shutter speeds, what benefit do we get from having it at all?

Obviously, it does go some way to protecting the sensor from dust and/or damage, but does it serve any purpose in the actual taking of the photograph? Do we get any visible benefit? Or is this more a hang-up from the film days ("We need a mechanical shutter because that's what SLR's have")?

Any thoughts?

[Onyx]

As I understand the shutter curtain has to physically move out of the way in order to expose the sensor to the light.

At shutter speeds faster than 1/250, the shutter's physical movement is no faster than 1/250 (saving wear and tear and extending its life - a good thing IMHO), the electronic circuits in the sensor merely flicks on and off to register less light - simulating these faster shutter speeds.
We can't have a strictly all electronic shutter without the mechanical part, as it would just be a frame of blackness.


Quoted from Thom Hogan's D70 review:

This arrangement first appeared on the D1 and provides one very useful side effect: flash sync speeds are increased substantially (arbitrarily limited to 1/500 on the D70, just like the D1 series). Single shot and continuous firing at 3 fps is supported, though it's relatively easy to (inadvertently) turn on features that would make motor drive even more leisurely in pace; obviously you can't get 3 fps if the shutter speed is 1/2 second, but Single Servo AF, red-eye reduction, autofocus assist and host of other things can eat into the maximum frame rate if you're not careful.

[sheepie]

But why can't we have a fully electronic shutter? In other words - why have anything mechanical at all? Is it just to protect the sensor, or is there an asthetic benefit?

[Matt. K]

Maybe they figure we just like to hear that shutter slap?

[gstark]

Quoted from Thom Hogan's D70 review:

This arrangement first appeared on the D1 and provides one very useful side effect: flash sync speeds are increased substantially (arbitrarily limited to 1/500 on the D70, just like the D1 series).

Not true.

By blanking off the two rearmost contacts on the D70's hotshoe (or using a flash that doesn't have contacts in those locations) you can get flash synch at all shuttewr speeds.

[Glen]

Leon, I think in the future you will be proven correct.
Matt, I picked up a copy of Nikon Pro when in the city last week and one whole page was devoted to an engineer who is the acoustic engineer for different Nikon models. He spends his whole life making sure they sound good. That must be why they made Birddy's D2X sound better than my D70. I also bet it will go like the shutter and in a few models there will be an electronic chip making shutter noises while wankers like me comment on how good it sounds

[Onyx]

It can't be fully electronic because you'll get a picture of pure black if there is no mechanics raising the shutter curtain to expose the sensor. If there is no shutter curtain completely, the sensor would constantly be exposed to the environment, making dust much more likely to settle on the low pass filter.

Also, IMHO this fully electronic shutter that you're proposing is what separates P&S sensors from SLR sensors. Apart of size and a host of other differences, SLR cameras by definition has mechanical bits such as the lifting mirror and raising of shutter curtains to distinguish it from P&S cams, which the sensor is constantly receiving light and feeding it to the rear LCD and only at the moment of shutter release electronically compiles what it sees onto the storage card.

[phillipb]

It can't be fully electronic because you'll get a picture of pure black if there is no mechanics raising the shutter curtain to expose the sensor. If there is no shutter curtain completely, the sensor would constantly be exposed to the environment, making dust much more likely to settle on the low pass filter.

Also, IMHO this fully electronic shutter that you're proposing is what separates P&S sensors from SLR sensors. Apart of size and a host of other differences, SLR cameras by definition has mechanical bits such as the lifting mirror and raising of shutter curtains to distinguish it from P&S cams, which the sensor is constantly receiving light and feeding it to the rear LCD and only at the moment of shutter release electronically compiles what it sees onto the storage card.

I think there has to be a more pragmatic reason for having the mechanical shutter other then to separate the P&S from the SLR.
The mirror should be sufficient to protect the sensor from extra dust and to stop a constant stream of light reaching the sensor.

[joolz]

Because then it wouldn't be an SLR (Single Lens Reflex) without the mirror. ie. you wouldn't see what the sensor will see when you fire the shutter.
You can't both see the same thing through the lens simultaneously. Though there are some partial mirrors out there, I think there must be some drawback to them such as division of the light source that mean that they are not used much.

[joolz]

Err, just realised you are talking about the shutter, not the mirror.

[sirhc55]

The mirror would not cover the sensor totally as it has a pass through function - it is not a mirror as we know it, i.e. a shaving mirror. I believe that this is one of the reasons that the D70 viewfinder is relatively dark.

If I am wrong I am sure someone will tell me

[MattC]

It probably has something to do with the powering of the sensor, exposing it to light at the beginning of the shot and charging and discharging of photosites. Having the sensor powered up and exposed to light prior to the shot being taken would mean that the sensor would need to be cleared (??) or discharged as in a P&S. Having the sensor power up prior to the shot behind a shutter would mean that there is no unwanted charging of the sensors photosites. As I understand it, this is still a bit of a problem with a P&S, that is, there may still be some residual charge remaining leading to degradation of image quality or longer shutter lag. It is relatively easy to stop the exposure electronically.

Hmmm... Hope I got that in the ballpark. I am sure someone will correct me if I am wrong.

With advancements in technology, I cannot but wonder at how long it will be before we see a dSLR without a mechanical shutter, at least at a consumer level.

Cheers

Matt

[pippin88]

The mirror would not cover the sensor totally as it has a pass through function - it is not a mirror as we know it, i.e. a shaving mirror. I believe that this is one of the reasons that the D70 viewfinder is relatively dark.

If I am wrong I am sure someone will tell me

What's the pass through fuction for? BTW, a mirror that doesn't reflect all light is usually called half silvered (well one that does half is, not sure how its refered to otherwise).

[sirhc55]

Part of the focus system - I will look it up and get back

[gstark]

Chris,

The mirror would not cover the sensor totally as it has a pass through function - it is not a mirror as we know it, i.e. a shaving mirror. I believe that this is one of the reasons that the D70 viewfinder is relatively dark.

If I am wrong I am sure someone will tell me

You're not wrong, but you're not entirely correct.

Yes, the central portion of the mirror is semi-silvered glass - if you remove your lens from your camera, you can see this - but there's a secondary mirror mounted behind the primary one, and it reflects what's been passed through to the metering and focussing mechanisms in the floor (iirc) of the mirror box.

[sirhc55]

Chris,

The mirror would not cover the sensor totally as it has a pass through function - it is not a mirror as we know it, i.e. a shaving mirror. I believe that this is one of the reasons that the D70 viewfinder is relatively dark.

If I am wrong I am sure someone will tell me

You're not wrong, but you're not entirely correct.

Yes, the central portion of the mirror is semi-silvered glass - if you remove your lens from your camera, you can see this - but there's a secondary mirror mounted behind the primary one, and it reflects what's been passed through to the metering and focussing mechanisms in the floor (iirc) of the mirror box.

Thanks Gary - I knew I was close

[sheepie]

OK - so it seems my initial thoughts were about right (now there's a change!)..

The shutter serves no real purpose other than the following:

- Protection of the Sensor Surface (which is largely already protected by the mirror/mirrors anyway)
- Makes us feel all warm and fuzzy because 'a real shutter is one of the things an SLR must have'

It seems, other than moving the mirror(s) out of the way, and obviously the lens itself, there is no real need for mechanics inside a DSLR!
Given this, and the rather worrying point of the shutter perhaps only lasting some 25-50k operations, shouldn't we just rip it out?

If this is all correct, then I can see a day close by when someone brave will release a 'shutterless' DSLR.
For those worried about the loss of sound ("click"), the retaining of the mirror system (which actually defines the SLR) would still enable the familiar confirmation a picture was indeed taken.

Be warned - be prepared! ...or should that be... Be afraid, be very afraid!

[digitor]

It probably has something to do with the powering of the sensor, exposing it to light at the beginning of the shot and charging and discharging of photosites. Having the sensor powered up and exposed to light prior to the shot being taken would mean that the sensor would need to be cleared (??) or discharged as in a P&S. Having the sensor power up prior to the shot behind a shutter would mean that there is no unwanted charging of the sensors photosites. As I understand it, this is still a bit of a problem with a P&S, that is, there may still be some residual charge remaining leading to degradation of image quality or longer shutter lag. It is relatively easy to stop the exposure electronically.

Hmmm... Hope I got that in the ballpark. I am sure someone will correct me if I am wrong.

With advancements in technology, I cannot but wonder at how long it will be before we see a dSLR without a mechanical shutter, at least at a consumer level.

Cheers

Matt

I think you've got it right Matt, I'm sure I've seen this sort of thing referred to before, but can't think where! As I understand it, keeping the sensor dark contributes to the very short shutter delay (in fact it's so short, it's more of a mirror delay with DSLRs) of the D70. I don't think that the shutter is included just for the acoustic value! A bloke at work has one of those slr look-alike digicams, which comes complete with a shutter/mirror/motordrive sound effect. Luckily you can turn the sound off if you want....

Cheers

[MattC]

I think, I saw this one on DPReview about a year ago. One of my favourite questions back then was "How do I turn of the shutter sound?" !!

I had one of those digicams with noises - CP5700 - at least the noise was relatively subdued and was more like a double click. I like my audio cues. I still rely on the noise my flash makes when recharging and AF beeps.

When I mentioned the shutterless dslr, I was thinking shutterless, not mirrorless (the bit that makes an slr) so still makes camera noises.

Cheers

Matt

[sheepie]

...keeping the sensor dark contributes to the very short shutter delay (in fact it's so short, it's more of a mirror delay with DSLRs) of the D70.

OK - I think I have seen something similar. So the shutter DOES make a difference at the moment. But it won't be too long b4 they get around that technical difficulty
At least I have some points to make now when I'm discussing the merits of SLR and the shutter comes up.

Thanks all