[Spock]

Why do DSLRs have mechanical shutters? Clearly the K7 (and almost every point-and-shoot) can record images without the need for a mechanical shutter - so why are they there?

[SteveM]

so you can see through the lens and not through the sensor. Your eye will always pick up more than the sensor....and hopefully the sensor will benefit from it. If they can figure out a way for there to be a mirror that can reflect the image to the viewfinder while having the image square on the sensor at the same time....that would be ideal.

[Spock]

so you can see through the lens and not through the sensor.

I think you are confusing the mirror with the shutter. DSLRs (and film SLRs) have both a shutter and a mirror that flips up just before the shutter opens.

I know why there is a mirror - but why the need for a shutter? The K7 can take 30 frames per sec with the shutter open (in movie mode).

[kittykat46]

An electronic shutter needs the sensor to be continuously "ON" - just like on a P&S. It takes one exposure from that continuous feed and makes that the captured image.

With a mechanical shutter, the sensor actually goes from complete darkness, exposure then complete darkness - it has a lot more time to be read and the residual charge completely bled off the sensor before taking the next photograph.

At this point of the technology - and I won't say it will always stay that way - the sensor circuity can be kept simpler with a mechanical shutter, and (probably) better IQ and noise control.

[jptreen]

the D40 managed it fine...as have a couple of others, and with great advantage.

...Its probably just that little bit easier not to, which is a shame. I'd love my cameras to sync at 1/4000!

PS - I know about HSS, but this isn't the same.

[and]

As far as I understood its more difficult to do that with CMOS sensors, same reason why they have jello effect in movies, because the whole sensor isnt read at the same time, as it is with a CCD sensor. So some sony CCD sensors had electronic shutters built in, but pentax never took advantage of it, only nikon did. I too would love to see that and to sync at 1/1000 sec without using HSS

[Marc Sabatella]

the D40 managed it fine...as have a couple of others, and with great advantage.

The D40 may have used an electronic shutter type of technology to get a higher sync speed than could be produced purely mechanically, but it still relied on its mechanical shutter for its basic operation.

[pingflood]

The D40 may have used an electronic shutter type of technology to get a higher sync speed than could be produced purely mechanically, but it still relied on its mechanical shutter for its basic operation.

Well, depends on what you mean by "basic operation".

The D40 uses a mechanical shutter with a top speed of 1/90 second. The faster speeds are done by opening the mechanical shutter for 1/90 second and the electronic shutter controls the rest. The higher sync speed is just an interesting and useful side effect of this setup, not the intent...

The 1/500 limit by the way I think is somewhat arbitrary and probably listed because it is longer than most flash durations (though some like the Metz 58 can have longer durations than that even...).

[Marc Sabatella]

What I mean by "basic operation" is that every picture you take still uses the mechanical shutter, and that if the mechanical shutter were removed, the camera would not be able to function. I hadn't realized the higher sync speeds were just a side-effect - are you implying it was really a cost-cutting meausre primarily?

[ytterbium]

Electronic shutter take up useful space (sensitive area) on ccd. To be more precise, every other row is used for shuttering instead of light collecting, as well as various other problems arise.

Unless you make a double sized ccd (basically a FF sized one for APS-C camera) with one side masked for image storage you're trading off something with electronic shutter. And even then you'd get smearing with bright light sources.

Various sensor types, their applications, advantages and diadvantages have been described in detail all over the internet. The rest you can figure out on your own.