Shutters and DSLR's

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Splog

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Hi all

Why do modern DSLR's actually need a shutter :thinking: surely this could be done electronically and not by a mechanical shutter?
 
LOL. Very good question actually!

I've no idea what the answer is, but the focal plane shutter in modern DSLRs takes a real battering especially since everyone now shoots a gazillion more shots than they ever did with film, forcing manufacturers to quote longer and longer estimated shutter lives, based on actuations, and they never seem long enough do they?

I really don't know what the technical reasons are for hanging onto the traditional shutter. I did read that tests had been done with liquid crystal shutter curtains, but they couldn't get the crystal opaque enough for the job.

The cynic in me thinks it's probably already cracked and due to be released a few models from now. ;)

EDIT.

Either that, or it's proved far too durable and been shelved. :D
 
Aren't there 2 parts to this question, shutter and mirror
Mirror is easy, you need it to view the subject through the lens obviously.
So you want to lose the shutter ? the mirror will still cover the film/sensor plane shutter or not, unless you do some sort of fancy light bend with prisms and wotnot.
I was thinking the shutter could be in the lens, a la leaf shutter lenses, but you still have that great big mirror flappin up and down, which I would have thought suffers more than a shutter with the stresses of actuation.
 
Haven't they already 'done' pellicle mirrors though which stay put?
 
pelican mirrors...:thinking:

are those the ones that are only mirror reflective at an angle or something ?

anyway, with a pellicle mirror the shutter could be in the lens, and a few extra hundred quid as well as crunch tax could be slapped on lens rrp..:D
 
Could just be a cheap and efficiant way of doing it and they dont see need to change as it works fine?
 
joxby said:
pelican mirrors...:thinking:

are those the ones that are only mirror reflective at an angle or something ?

anyway, with a pellicle mirror the shutter could be in the lens, and a few extra hundred quid as well as crunch tax could be slapped on lens rrp..:D
Click to expand...

LOL. I think the idea was the light was split, with some going up to the viewfinder and the rest going to the sensor.
 
The longer that photosites are exposed to light whilst charged then the higher the level of noise. I would imagine that the technology to switch on, read and switch off upwards of 21 million sensors in 1/8000 second, is far far away at the moment. Add to that the increased exposure to dust and the shutter curtain is a bonus and not a weakness....until it fails.

Bob
 
Good point Bob, probably a lot more difficult than we may think.
 
Well personally, I just like the sound it makes :D
 
ChrisMClark said:
Well personally, I just like the sound it makes :D
Click to expand...
In similar vein - when I was doing a lot shooting, my mate used to say "Would we still shoot if the gun didn't go 'bang!'? "":shrug:
 
You need a mirror for viewing and phase-detect AF, so you might as well stick a shutter in there too. But it won't be long before that goes. The problem is in switching the sensor on and off rapidly, combined with the need for continuous viewing.

Panasonic has shown a glimpse of the future in the G1, which is an interchangeable lens 4/3rds format camera. It has no mirror and uses an optical viewfinder and contrast-detect AF. It works very well apparently. They just need to get the sensor to switch as well as a shutter does for accurate exposure, and the DSLR as we know it will be history.

Given the pace of sensor development at the moment, I'm sure cameras like this already exist in R & D departments. When they're sorted, the advanatges will be real and fundamental. I can't wait!
 
Casio already has a compact model that does 40 fps or a 1000 fps video, turning the sensor on and off doesn't sound the problem. Wayne
 
swanseamale47 said:
Casio already has a compact model that does 40 fps or a 1000 fps video, turning the sensor on and off doesn't sound the problem. Wayne
Click to expand...

I don't get that either, but then this aspect of sensor technology doesn't get much talked about.

Can somebody explain why with cameras like the G1 there is such a convoluted operating sequence. Shutter is open for viewing when you press the button, then the shutter closes and the sensor turns to record mode, shutter opens, pictures is taken, shutter closes and sensor returns to viewing mode, shutter reopens for viewing.

I wonder if initial lag is the problem? Or there is some difficulty controlling exposure time with the G1's sensor that doesn't apply to the Casio? Is there some conflict between speed and image quality? (I think the Casio uses only a handful of pixels at max fps.) Is the a fundamental difference between different sensor types, like CMOS and CCD?

The problem is undoubtedly with the sensor, but I don't know what it will take to get rid of the mechanical shutter.
 
Update on my post above:

I've often wondered how these high speed Casios work, so I phoned them. "Why does the FH-20 have a mechanical shutter when high speed images are recorded purely electronically?"

To cut a long story short, being shunted between various departments including technical support, none of whom even understood my question let alone had the answer, one helpful guy said he'd speak to a Japanese colleague and get back to me.

The question is further confused by the fact that the camera is actually recording all the time, and can recall images from the buffer taken fractionally before the button was even pressed.

I would love to use this camera for birds in flight, but since action photographers have not been rushing out to buy these astonishing Casios, there must be a catch. I'd really like to know what's going on. I'll let you know what I find out.

How do video cameras work? How do they control exposure? Can they alter the exposure time within the frame rate? Or is all exposure control done with varying sensitivity (ISO) and lens aperture?
 
Ally said:
Indeed my EOS RT has one. The only difference is theirs no shutter slap.
Click to expand...
I'm sure the drawback was -2/3 of a stop light loss due to the pelicle mirror affair.

Didn't the original 1D do some clever stuff about turning the sensor on/off to achieve the increbibly high shutter speed? Or am I imagining things...

edit - the original 1D did have an electronic shutter that allowed it to achieve 1/16000 s shutter speed. So it can be done, although that was a CCD sensor no CMOS, could make a difference?
 
RichardtheSane said:
I'm sure the drawback was -2/3 of a stop light loss due to the pelicle mirror affair.

Didn't the original 1D do some clever stuff about turning the sensor on/off to achieve the increbibly high shutter speed? Or am I imagining things...

edit - the original 1D did have an electronic shutter that allowed it to achieve 1/16000 s shutter speed. So it can be done, although that was a CCD sensor no CMOS, could make a difference?
Click to expand...

The pellicle mirror was a good idea, and Canon persisted with it for quite a while, but there were lots of problems. Loss of light to the film and also to the viewfinder, fragile and hard to clean, degraded image quality a bit, and you can't hang a piggy-back mirror off it for AF.

Good point about the Canon 1D, but it still had an entirely conventional focal plane shutter, and also, I notice that the 1/16,000sec feature has now been removed, and the CCD sensor replaced with CMOS. Why is that then?

All of which adds to more questions than answers.
 
Quite a few Nikon CCD cameras have combined mechanical and electronic shutters.

CCDs are interesting beasts. They read out data by shunting it across pixel by pixel, which must be done in complete darkness - so a shutter somewhere is handy. However, some CCDs (the ones in some motion cameras without rolling shutters) have lines which can take a charge but aren't sensitive to light, so a line of data can be shunted down/across and then read out before the next "exposure" (or in fact in twice the time of the exposure). Read this for the difference between full frame, frame transfer and interline CCDs.

CMOS sensors are a bit more useful for this though. You can read data off them almost like a focal plane shutter (start at one end, work to the other). As far as I can tell, the only reason we don't have electronic shutters on our CMOS cameras is that the A/D converters aren't yet up to the performance needed for acceptable pro-level frame rates with a high megapixel count. I strongly suspect that people smarter than us are working on it as we speak.

CCDs were replaced with CMOS because CMOS has had a lot more research recently and is now cheaper for the same performance. The advantage of a CMOS sensor is that it doesn't need to be kept in the dark, so it can be used for things CCDs can't like live view or a better movie mode. They've been used as light meters for a long time now.
 
I just hope they keep them for the sound as said before... love the sound... especially on rappid fire!

M
 
Very interesting question, never really given it much thought, but I did wonder how the hell they produced those staggeringly quick bridge cameras which shoot at 60fps or whatever.
 
I am I the only one who would love a silent shutter? My 40D sounds like a flipping machine gun on high speed -just like every other one I've heard -Me wants silence when I shoots!!! - Probably why I love sniper rifles in fallout 3 et al :clap:-

Tara
 
I heard a rumour of the new gen DSLRs not having mirrors, and shutters the viewfinder being a digital screen.

There was a guy talkign to me about it, and I thought YUCK, but he seemed to like the idea, and had a whole host if reasons (including silent usage, less chance of camera shake whenthe shutter "snaps" shut and many more) I was too busy thinking that I woudl miss looking through the lens to really apreciate what he was saying
 
Blapto said:
Quite a few Nikon CCD cameras have combined mechanical and electronic shutters.
Click to expand...


:thumbs:, its the reason D70's achieve 1/500th flash sync, when everyone else was at 1/250th..

god I miss my D70 :(
 
I was gonna write a long spiel about mirrors/shutters being unnecessary but this thread has got me thinking. The main reason imo for shutters and mirrors still being used in SLRs is purely because of the fact it aint broken (so why fix it). Various companies have been using lcd viewfinders in compacts for years, the only thing keeping them from moving over to SLRs aswell is the fact the folding mirror arrangement works well, so the developement in LCD view finders is a bit behind.

Also looking at current technology (eg camera phones) the shutter arrangement is also out dated really, as taking photo can simply be a case of 'print screening' the image from the sensor like on phones. This is merely a case of adapting in camera processing to accomodate it.
 
Blapto said:
Quite a few Nikon CCD cameras have combined mechanical and electronic shutters.

CCDs are interesting beasts. They read out data by shunting it across pixel by pixel, which must be done in complete darkness - so a shutter somewhere is handy. However, some CCDs (the ones in some motion cameras without rolling shutters) have lines which can take a charge but aren't sensitive to light, so a line of data can be shunted down/across and then read out before the next "exposure" (or in fact in twice the time of the exposure). Read this for the difference between full frame, frame transfer and interline CCDs.

CMOS sensors are a bit more useful for this though. You can read data off them almost like a focal plane shutter (start at one end, work to the other). As far as I can tell, the only reason we don't have electronic shutters on our CMOS cameras is that the A/D converters aren't yet up to the performance needed for acceptable pro-level frame rates with a high megapixel count. I strongly suspect that people smarter than us are working on it as we speak.

CCDs were replaced with CMOS because CMOS has had a lot more research recently and is now cheaper for the same performance. The advantage of a CMOS sensor is that it doesn't need to be kept in the dark, so it can be used for things CCDs can't like live view or a better movie mode. They've been used as light meters for a long time now.
Click to expand...

Interesting post and link Blapto. Thanks :thumbs:

So, we already have a camera using interchangeable lenses with no optical viewfinder and contrast-detect AF that works, in the shape of the Panasonic G1. But it still has a conventional focal plane shutter. And at the same time we have compacts that work well without a mechanical shutter.

The problem can only be that whatever is being done with compacts is not good enough to deliver the higher imaging standards expected of a DSLR - lag, frame rates, sharpness/pixels, noise. As you say, "I strongly suspect that people smarter than us are working on it as we speak." And a solution cannot be far off.

Then we'll have a solid state camera - zero shutter delay, no mirror/shutter noise or vibration, incredible frame rates, flash sync at all speeds, a viewfinder that shows depth of field clearly, amazing subject-tracking AF that works at any f/number, lenses that are smaller/lighter/cheaper/better, stacks of viewfinder info. All sounds good to me :)
 
Getting rid of the mirror would allow for much more efficient lens design, though only to a point. I remember reading something that Epson put out when they made the first digital rangefinder, the issue they found was that the microlenses on the sensor wouldn't accept light at the same angle as film would. They said at the time that was the reason for the 1.5x crop factor (though it was probably half that and half economics).
 
Blapto said:
Getting rid of the mirror would allow for much more efficient lens design, though only to a point. I remember reading something that Epson put out when they made the first digital rangefinder, the issue they found was that the microlenses on the sensor wouldn't accept light at the same angle as film would. They said at the time that was the reason for the 1.5x crop factor (though it was probably half that and half economics).
Click to expand...

It's true that getting rid of the mirror allows the lens rear element to sit closer to the film/sensor for virtually distortion free wide angle images. The problem is that wide angle lenses can sit so close to the sensor that light falls off towards the corners and edges of the image an a full frame camera, so I suspect that this had a lot to do with Epson opting for the 1.5 crop format.

The Zeiss Hologon 16mm F8 for the Contax G2 is a good example. It comes with a darkened centre spot filter to combat the light fall off. The filter requires a further 2 stops of compensation, making a fixed F8 lens not the easiest of lenses to use in all but very good light.
 
Interesting possibilities with lenses, in theory, if you can position the lens optimally in relation to the sensor, without the need to clear the mirror. No need for retrofocus designs. But I'm not sure how far this will go in practise, or indeed the need for it. Lens designers have been working around reflex mirrors for so long that they seem to have got it cracked. Certainly my Canon EF-S 10-22mm is astonishingly good.

And then there are the problems highlighted above, where digital sensors don't accept light at an angle like film does at the edges and corners, coupled to the natural fall-off of light when the lens is close to the film/sensor - the centre of the image is much nearer than the edges. And then when you add these consideratioons to the huge lens legacy that Nikon/Canon and others have got I guess the propsect of ditching all that for a marginal benefit is less than appealing.

Leica faced exactly these 'opportunities' with the M8 and the result, IMHO, is a completely bodged mess. The wonderful purety of the Leica film camera has been entirely lost, and none of the benefits of digital have really transferred through. It's a horrible bodge and has probably killed Leica (not that there was much life left in it).

So I would like to offer a solution! All we need is a concave-shaped sensor - not flat like a plate, but curved like a saucer or shallow bowl. Sorted :D To those that know about these things: is there any way, at all, ever, that this might happen? A concave sensor would make much more difference to lens deisgn than merely getting rid of the mirror. With film it was entirely out of the question of course, but with digital?

(Actually what we need is a sensor with a variable curve, to suit both wide angles and telephotos. I guess that is maybe asking too much ;) )
 
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