Purpose of shutter on digital camera?

Nikon's using more CMOS now I hear.

The start-up and shut down characteristics of the sensor is non-linear and trying to have an electronic shutter would introduce a whole new set of problems to solve. The turn-on and turn-off transition also occurs slowly. This could be problematic for the very fast shutter speeds. However, the biggest problem would be in reading the data into a buffer since it does not happen simultaneously for every pixel in the array. The last pixel to be read would have data that has had longer exposure and also at a later instant in time than the first pixel to be read.

Remember also that the sensor itself is an analog device that interfaces between the real analog world and the electronics that quantize its output and convert it to a digital signal for storage and processing. Think of each pixel as a rain gauge that gathers light over a finite length of time. To have a coherent image. all of the data needs to be captured with essentially the same beginning and ending time. After the shutter closes, the read process and the sensor refresh process can take place.

Not an expert regarding why, but I have worked as a technician (not engineer) for about 20 years in both analog and digital electronics. Keep in mind that the sensor in a Digital SLR is in fact an analog device. It is a network of photoelectric cells that emit an analog voltage according to how much light it receives. That voltage is then digitized by an analog-to-digital converter and processed into a picture we can use.

Also keep in mind that our DSLRs provide shutter speeds far in excess of (I think all) shutter-less P&S cams. I can not imagine being able to turn on, and then off again, an analog device at 1/8000 of a second and still get the accurately exposed results we expect. To my mind it makes a lot more sense to power up the sensor first and then let the proven mechanical two-curtain shutter gives us that metering accuracy. The rise and fall times of those photo cells could not possible be fast enough or clean enough to perform to that level. Maybe someday, but I don’t think we’re there yet. Just my opinion though!

bill boehme wrote in post #2638845
Remember also that the sensor itself is an analog device that interfaces between the real analog world and the electronics that quantize its output and convert it to a digital signal for storage and processing.

Ahhh... Beat me to the submit key!

Moppie wrote in post #2638202
It works well on compacts, with thier smaller sensors, and I know sony made it work with a APS-C sized CCD sensor.

But, I don't know how well it would work on a full sized CMOS sensor?

That said, Sony success shows no need for a shutter in the DSLR brands that use CCD sensors.

I think it just shows they SLR's are old technology, and the manufactors are being very reluctant to change.
What I want to know is that reluctance coming from the consumer or the manufactor?

Are you saying that Alphas don't have a shutter? Not true.
I wasn't aware that digital compacts were shutterless. Don't most have two blades that perform as both shutter and aperture, or is that just film compacts?

And I can't accept that DSLR manufacturers stay with a complicated and fragile mechanical assembly out of choice - if they could acheive the same with software or a chip, then I'm sure they would.

bill boehme wrote in post #2638845
The start-up and shut down characteristics of the sensor is non-linear and trying to have an electronic shutter would introduce a whole new set of problems to solve. The turn-on and turn-off transition also occurs slowly. This could be problematic for the very fast shutter speeds. However, the biggest problem would be in reading the data into a buffer since it does not happen simultaneously for every pixel in the array. The last pixel to be read would have data that has had longer exposure and also at a later instant in time than the first pixel to be read.

Remember also that the sensor itself is an analog device that interfaces between the real analog world and the electronics that quantize its output and convert it to a digital signal for storage and processing. Think of each pixel as a rain gauge that gathers light over a finite length of time. To have a coherent image. all of the data needs to be captured with essentially the same beginning and ending time. After the shutter closes, the read process and the sensor refresh process can take place.

Sorry but as an EE with a masters in computer science, this holds as much water as the theory that the earth is flat.

chris clements wrote in post #2638922
Are you saying that Alphas don't have a shutter? Not true.
I wasn't aware that digital compacts were shutterless. Don't most have two blades that perform as both shutter and aperture, or is that just film compacts?

And I can't accept that DSLR manufacturers stay with a complicated and fragile mechanical assembly out of choice - if they could acheive the same with software or a chip, then I'm sure they would.

If the P&S digital cameras had mechanical shutters that stayed closed until just before they took a picture, then they'd be in the same boat as most DSRLs as far as live previewing is concerned, wouldn't they?

sWampy wrote in post #2639073
Sorry but as an EE with a masters in computer science, this holds as much water as the theory that the earth is flat.

EE here also with 30+ years in digital electronics - real hardware as opposed to CS.

bill boehme wrote in post #2638845
The start-up and shut down characteristics of the sensor is non-linear and trying to have an electronic shutter would introduce a whole ...............the shutter closes, the read process and the sensor refresh process can take place.

Lacks_focus wrote in post #2638889
Not an expert regarding why, but I have worked as a technician (not engineer) for about 20 years in both analog and digital electronics. Keep in mind that the sensor in a Digital SLR is in fact an analog device. It is a network of ...............or clean enough to perform to that level. Maybe someday, but I don’t think we’re there yet. Just my opinion though!

You both make a lot of sense, and it would explain the limited max shutter speeds on compacts. Iv yet to see one with a shutter speed faster than 1/2500th of a second.

chris clements wrote in post #2638922
Are you saying that Alphas don't have a shutter? Not true.
I wasn't aware that digital compacts were shutterless. Don't most have two blades that perform as both shutter and aperture, or is that just film compacts?

And I can't accept that DSLR manufacturers stay with a complicated and fragile mechanical assembly out of choice - if they could acheive the same with software or a chip, then I'm sure they would.

The Sony Alpha has a shutter, never said it didn't.
However, Sony also made a compact (thats actualy bigger and heavier) with a fixed lens, no shutter, and an APS-C sized sensor. I think it was called the H1 or something.

There are lots of things that manufactors can do, but for any number of reasons don't.
Olympus has shown its possible to have a DSLR with selectable live preview. Sadly its poorly implemented.
Its easy to forget that its the consumer who ultimately makes the choice about what products and services he or she uses, and encourages the providers to allow access to, but we all to often fall into the trap of taking what we are given, or told we should have via marketing, rather than looking more rationaly at what we really want or need, regardless of what we are told.

At the moment we are told that DSLR's need to have a shutter, and so far we have found some evidence as to why, however, the next quote suggests other wise...............

sWampy wrote in post #2639073
Sorry but as an EE with a masters in computer science, this holds as much water as the theory that the earth is flat.

Can you explain further please?
A blank statement with no surporting argument holds about as much water as a flat earth would.

Moppie wrote in post #2639301
Can you explain further please?
A blank statement with no surporting argument holds about as much water as a flat earth would.

Thanks, Moppie, let's stick to discussing technical issues and forget about flaunting credentials. I've never been able to overcome a technical challenge by assaulting it with credentials.

Moppie wrote in post #2639301
The Sony Alpha has a shutter, never said it didn't.

Since the Alpha is Sony's only DSLR to date, how else was I to interpret "Sony success shows no need for a shutter in the DSLR brands that use CCD sensors."

PacAce wrote in post #2639201
If the P&S digital cameras had mechanical shutters that stayed closed until just before they took a picture, then they'd be in the same boat as most DSRLs as far as live previewing is concerned, wouldn't they?

... I'm off to the corner of the classroom now!

sWampy wrote in post #2638575
Having rapair item that costs 25% of the cost of the original item, that almost breaks after warranty is up, with a none failure rate, that is cheap for you to replace, but impossible for others to replace, might not be logical to you, but I'm sure automobile makers, computer makers, appliance makers would differ with you.

I wish I understood what you wrote...your grammer is horrible. Please rephrase....

Moppie, Fuji P&S's have 1/4000 shutter speeds. Just so you know! Which is far from 1/8000, but you know what I mean.

SLR's have shutters because they're SLR's. By definition they have shutters and mirrors. They just have. So there.

I think it was Moppie who discussed this ages ago with soemone else, saying that SLR's are dinosaur technology, which is true but doesnt mean that the technmology is rubbish. A shutter allows very fast start-up times, faster shutter speeds, faster FPS in continuous shooting and the biggie: It makes a cool noise.

IF noise was the important factor, wouldn't it be more effective to leave out the mechanical shutter and put in a Dolby sound system that sounds like a real shutter?

I'm not an EE, but I imagine it is easier or more accurate to measure all the light reaching each sensor site for the brief time the shutter is open than to coordinate the measurement of light reaching all the sensors for the same peoriod of time. This may result in a cleaner image with less noise.