Electronic vs Mechanical Shutters

[dje]

Sometimes we take things for granted and until now, shutters have been one of those things for me. But recently I have had cause to think about this a bit more and am a bit puzzled.

As far as I'm aware, most DSLR's use mechanical shutters although I believe some of the recent Sony models have an electronic front curtain option. On the other hand, compact cameras pretty much use electronic shutters. The sensor type (CCD vs CMOS) is also a factor.

Can anyone give me an explanation of why certain types are used where or point me to a good article ? I don't think this is covered in the CiC tutorials but I may have missed it.

Thanks
Dave

[Manfred M]

Something to remember about all sensors is that they contain more than just the individual photodetector, they also contain other electronics. I the basic DSLR sensor also contains amplifier circuitry as well. This takes up space and reduces the light capture capacity. It does not need any internal buffering for the amount of light that I captures as the data transfer; anything that is captured is good data and is dumped into the upstream A/D converter. The trigger is obviously the mechanical shutter; it only records light while the shutter is open and bleeds off charge when it is closed

The electronic shutter is more complicated. As light continuously hits the sensor, when the exposure is started, additional circuitry has to accumulate the number of photons captured (there is no light /dark of the mechanical shutter here) The amount of light in each photodetector is a counted during the exposure window. This circuitry is built into the photodetector, and this takes up space, reducing the overall area that can be used to capture photons; this in turn reduces sensitivity and requires more amplification = higher noise.

So in a DSLR, where low noise and high gain are required, we see a focal plane shutter whereas in the cheap point & shoot cameras, we see the less expensive, but lower quality output electronic shutter.

[NorthernFocus]

To further confuse the issue, now DSLRs have "silent live view" mode. Which if I understand correctly is basically electronic shutter. I also have a Nikon 1 body which lets you choose mechanical or electronic. As explained by manfred, in theory the mechanical shutter mode will produce less noise. Not sure that it shows from a practical standpoint unless you are doing really fine work.

[AB26]

Hi Dave,

This might make sense to you: http://www.steves-digicams.com/knowl...-shutters.html

[Letrow]

I wonder if the differences would be visible with today's technology.
On the Nikon 1, as Dan pointed out there is both the mechanical and the electronic shutter. I like the mechanical shutter better, because it produces noise, but the electronic shutter is fine if you need silence or (perhaps more relevant) higher shutter speeds.

[dje]

Thanks everybody for the comments and reference. These have helped me focus on the significant issue which is the inclusion of extra circuitry on a CMOS sensor to get an electronic shutter and the subsequent effect on sensor performance. This is, I believe, what is called a global electronic shutter. The other option is a rolling electronic shutter which doesn't require this extra circuitry but has other limitations in terms of speed of retrieving the pixel data. I think this is used for video on DSLR's which, even for HD resolution, has a lot less data and much slower shutter speeds to contend with than high res still imaging.

Dave

[pnodrog]

Hi Dave,

This might make sense to you: http://www.steves-digicams.com/knowl...-shutters.html

Hi Andre I read the article and I think it relates to 3T and some early 4T (T = number of transistors per pixel) designs and was written in 2007. Since then the technology has advanced with some sensors now able to integrate(sample) while the previous capture is still being read. This ability completely changes the requirement or function of mechanical shutters and also eliminates the rolling shutter problem in video applications. I understand the Sony sensor (IMX094) used in the Nikon D800 is based on the functionality of a 5T design but two of the transistors are shared with an adjacent pixel. However 6T designs are in the pipeline.

The advancements in sensor technology and production techniques are very rapid but I think the cost of using a mechanical shutter verse the declining benefits it brings means they will probably be phased out over the next 10 years. The 10 years is my guess but it may even be quicker (D900?) It is very interesting to try and follow the progress.

[Manfred M]

The advancements in sensor technology and production techniques are very rapid but I think the cost of using a mechanical shutter verse the declining benefits it brings means they will probably be phased out over the next 10 years. The 10 years is my guess but it may even be quicker (D900?) It is very interesting to try and follow the progress.

I have had similiar thoughts too, but wonder what they will do to protect the sensor from dust. The mechanical shutter serves a secondary purpose of shielding the sensor from all the stuff floating around in the mirror chamber. On the other hand, the interchangable lens mirrorless cameras already handle that issue.

[dje]

Hi Andre I read the article and I think it relates to 3T and some early 4T (T = number of transistors per pixel) designs and was written in 2007. Since then the technology has advanced with some sensors now able to integrate(sample) while the previous capture is still being read. This ability completely changes the requirement or function of mechanical shutters and also eliminates the rolling shutter problem in video applications. I understand the Sony sensor (IMX094) used in the Nikon D800 is based on the functionality of a 5T design but two of the transistors are shared with an adjacent pixel. However 6T designs are in the pipeline.

I've got to ask L.Paul, where do you get this sort of detailed information ?

Dave

[pnodrog]

I have had similiar thoughts too, but wonder what they will do to protect the sensor from dust. The mechanical shutter serves a secondary purpose of shielding the sensor from all the stuff floating around in the mirror chamber. On the other hand, the interchangable lens mirrorless cameras already handle that issue.

No shutter, no mirror and no Anti-Aliasing or Optical Low Pass Filter filter a camera will become so cheap we will just throw it away if it gets dust on the sensor.

I've got to ask L.Paul, where do you get this sort of detailed information ?

Dave

Dave you must know New Zealand is a very advanced country.

However it is all available by searching the internet. One source is Image sensors world but there are articles by sensor manufactures and also there is the odd thesis paper from Universities where the paper reviews the current technology and then proposes an advancement. A lot of the articles put up on photographic sites are out of date by the time we spot them.

Another important current advancement is the backlit pixel design which allows the transistors and other elements in the circuit to not interfere with the light path to the photo-diode. This improves efficiency and gives the designer more space to add complexity to the rest of the circuit. It is a bit like in a car putting the engine behind the driver to give him a better view and allowing the engine to be bigger.

[NorthernFocus]

... in theory the mechanical shutter mode will produce less noise. Not sure that it shows from a practical standpoint unless you are doing really fine work.

It occured to me that my prior comment needs clarification. The mechanical shutter produces less electronic noise but the electronic shutter produces less mechanical noise....

[dje]

It occured to me that my prior comment needs clarification. The mechanical shutter produces less electronic noise but the electronic shutter produces less mechanical noise....

But the mechanical shutter noise is "good" noise I still like that sound, and even on my compact I have simulated shutter noise turned on !

[dje]

dave you must know new zealand is a very advanced country.

Absolutely !

Thanks for the link. It seems to have a lot of information - whether my rapidly decaying grey matter can decipher it is another matter

Dave

[lfd]

This might make sense to you: http://www.steves-digicams.com/knowl...-shutters.html

Helped me, but he just ignored the whole class of Four Thirds and pseudo APS‐C sensors.

[davidedric]

Well, yes, but the thread is almost a year old, and I can't easily see a date on the linked article. Maybe it just reflects how quickly things have moved in the non-dslr world.

Oh, and welcome to Cambridge in Colour, Leandro.

Dave