---Nearly all digital cameras have a mechanical shutter. Only very simple
cameras rely upon capture timing with the sensor alone.
I would have thought that the vast majority of digital cameras were P&S without shutters?
Nearly all the point and shoots have a shutter, Rob, unless you mean cameras like the AIPTEK PenCam. Go check it out.
---From: Peter Williams <[EMAIL PROTECTED]>
Do you consider the KM A2 very simple? It hasn't got a shutter.
---From: Rob Studdert <[EMAIL PROTECTED]>
Neither do the Olympus E-10/20 SLRs
---From: Peter Williams <[EMAIL PROTECTED]>
Indeed I think that is the case. It is only the dslr type sensors which must be in the dark for the charge to be read off and stored. ... Indeed, I think Godfrey has somehow got a sync problem on this one.
From: Don Sanderson <[EMAIL PROTECTED]>
If they have a shutter, how can they do a full time preview on the LCD?
I'm rather astonished that you are all so misinformed and do not understand how digital cameras and digital SLRs operate with regard to the sensor and shutter...
Peter,
If you look down the barrel of the lens of your A2 and release the shutter, you'll see the shutter operate.
Rob, The same thing for the Olympus E10/20.
Don, The way small sensor digital cameras work is like this:
- Normal focusing/framing/viewing mode, the shutter is OPEN and the sensor chip is in "live acquisition" mode, refreshing its buffer according to the set refresh rate (30 or 60 fps on the KM A2).
- At the time you press the shutter release to make an exposure, the camera:
* Sets the focus and exposure values
* Closes the shutter
* Clears the sensor buffer, switches the sensor to "image capture" mode
* Closes down the aperture
* Operates the shutter
* Copies the sensor buffer to the image processing buffer
* Resets the aperture to fully open
* Reopens the shutter
* switches the sensor back to "live acquisition" mode
The large sensors used in DSLR cameras do not have the "live acquisition" mode and have a mirror in the way, so the shutter is operated just as it is in a film SLR. The lengthy sequence of operations a small sensor digicam has to do to acquire an image is one of the reasons why they do not respond to the shutter as quickly as a DSLR ... in a DSLR, the sensor can *always* be ready for the shutter to operate so shutter release lag is limited to the mechanical things that any SLR has to do (close down the aperture, flip up the mirror, trip the shutter).
Mechanical shutters are used because they allow precise and reliable exposure timing. IN some cameras, the manufacturers have enabled a combination of mechanical and sensor timing mechanisms to allow greater selection of speeds or shorter then mechanically possible exposure times (the Oly E10/20 have the former, the Nikon D70 has the latter IIRC), but these are the exception rather than the rule.
Godfrey
