Why does a digital SLR camera need a shutter?

[atvinnys]

a fellow of mine asked this question ...

Can someone explain to me the technical reason that DSLRs need to have shutters? Can’t this function be handled by image being “pulled” off of the sensor?

any ideas?
Thanks

[shutter]

Originally Posted by atvinnys

a fellow of mine asked this question ...

Can someone explain to me the technical reason that DSLRs need to have shutters? Can’t this function be handled by image being “pulled” off of the sensor?

any ideas?
Thanks

I don't know the exact details, but the CCD or CMOS sensor is sensitive to light. If you remove the shutter and have constant light upon the sensor the image you will get is an overexposed picture (all white).

Because the CCD or CMOS sensor is sensitive to light a shutter is required to control how much light exposes onto the sensor.

[McQ]

...and the read-out process from the camera sensor takes time. Just think, high-end SLR's can only do 8-10 frames per second. If a good fraction of the time spent in between frames is because of the read-out speed, then not using a shutter would really limit the range of exposure times you could do, among other things. You could end up with one part of the image being exposed differently than the other, or overexposed entirely. I also suspect that the pixel signals need to remain constant on the sensor during the read-out process for the noise reduction circuitry to work properly.

You pretty much still need something which very quickly and evenly starts exposing the sensor to light, and then stops it at just the right time. Anything which limits the light reaching the camera sensor to a precise time will suffice, so this does not necessarily have to be a mechanical shutter. You could even have an LCD-style device in front of the camera sensor which acts as a non-mechanical shutter. From what I understand a portion (the initiation) of the shutter during Live View is actually electronic. A mechanical shutter in a digital SLR is therefore not an absolute must; it's just the best/cheapest solution the camera companies have arrived at thus far...