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Photo Forum / Digital Photography / DSLR Cameras / February 2006Why do digital cameras need shutters?
I hope this isn't a silly question. Is it impossible or too expensive to turn the sensor on and off or something instead of a mechanical shutter? Just wondering. Steve > I hope this isn't a silly question. Is it impossible or too > expensive to turn the sensor on and off or something instead of a > mechanical shutter? Just wondering. It's possible, but slow and inaccurate. It is found on some cheap (phone) cameras.  SignatureMåns Rullgård mru@inprovide.com > > I hope this isn't a silly question. Is it impossible or too > > expensive to turn the sensor on and off or something instead of a [quoted text clipped - 6 lines] > Måns Rullgård > mru@inprovide.com Thanks How can it be inaccurate? Isn't there a processor clock that could time "shutter speed"? Just wondering and stubborn, too. Steve > How can it be inaccurate? Isn't there a processor clock that could time > "shutter speed"? Just wondering and stubborn, too. The clock would be accurate enough, but the response time of the sensor (both on and off) might not be. Merritt > > I hope this isn't a silly question. Is it impossible or too > > expensive to turn the sensor on and off or something instead of a > > mechanical shutter? Just wondering. > > It's possible, but slow and inaccurate. It is found on some cheap > (phone) cameras. Not quite true. The Canon EOS1D used its CCD to control exposure while the shutter was reduced to protecting the imager and keeping dust off, it also meant you could use a 1/500th sec flash sync. The MkII which replaced it (and MkIIN) use a CMOS imager so it's back to using the shutter for controlling exposure, and sadly back to 1/250th sec flash sync. Cheers, Tony SignatureNewcastle upon Tyne, England (Email address is valid ... for now) >> > I hope this isn't a silly question. Is it impossible or too >> > expensive to turn the sensor on and off or something instead of a [quoted text clipped - 13 lines] >Cheers, >Tony Flash synch, 1/4000th of a second. Not a DSLR. http://www.pbase.com/andersonrm/image/53920181 > Flash synch, 1/4000th of a second. Not a DSLR. Yeah, SLRs without electronic shutters can do that too. That's not really flash sync. SignatureJeremy | jeremy@exit109.com > I hope this isn't a silly question. Is it impossible or too expensive to >turn the sensor on and off or something instead of a mechanical shutter? >Just wondering. > >Steve Another reason is that it protects the sensor from things like accidental exposure to the sun, as even if the camera was off you could accidently point it at the sun and damage teh sensor. > I hope this isn't a silly question. Is it impossible or too expensive to > turn the sensor on and off or something instead of a mechanical shutter? > Just wondering. In addition to the other replies I believe the camera manufacturers also use the shutter as a black reference to measure sensor native noise. The Nikon D70 "electronically" shutter flash syncs up to 1/500 which is on the "closing" side of the cycle, and I think that should be standard on all high end DSLR's. Cheers, Alan Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. > The Nikon D70 "electronically" shutter flash syncs up to 1/500 which is > on the "closing" side of the cycle, and I think that should be standard > on all high end DSLR's. You can only do that with a CCD sensor, not with a CMOS. SignatureJeremy | jeremy@exit109.com >>The Nikon D70 "electronically" shutter flash syncs up to 1/500 which is >>on the "closing" side of the cycle, and I think that should be standard >>on all high end DSLR's. > > You can only do that with a CCD sensor, not with a CMOS. I didn't know that. Source? Signature-- r.p.e.35mm user resource: http://www.aliasimages.com/rpe35mmur.htm -- r.p.d.slr-systems: http://www.aliasimages.com/rpdslrsysur.htm -- [SI] gallery & rulz: http://www.pbase.com/shootin -- e-meil: Remove FreeLunch. >>>The Nikon D70 "electronically" shutter flash syncs up to 1/500 which is >>>on the "closing" side of the cycle, and I think that should be standard [quoted text clipped - 3 lines] > > I didn't know that. Source? You can technically have an electronic shutter with CMOS, but not without compromise; it's a pretty standard feature of CCD sensors. A quick google turned up: http://www.dalsa.com/shared/content/Photonics_Spectra_CCDvsCMOS_Litwiller.pdf Page 2 of that article has a pretty good description of the difference. SignatureJeremy | jeremy@exit109.com >> I hope this isn't a silly question. Is it impossible or too expensive to >> turn the sensor on and off or something instead of a mechanical shutter? >> Just wondering. > >In addition to the other replies I believe the camera manufacturers also >use the shutter as a black reference to measure sensor native noise. For "noise reduction mode" for long exposures; yes. For normal purposes, cameras may use blind pixel borders on the sensor. The 20D, for example, has a vertical strip of 74 pixels wide on the left side of the image, and a horizontal strip 12 tall on the top. The data from these is where the JPEG engine and RAW converters get their black values from (and they serve a s a noise sample as well). They are actually contained in the RAW .cr2 file, and black is left with the offsets still in them and in the exposed image (average is typically 128.2 to 128.4). >The Nikon D70 "electronically" shutter flash syncs up to 1/500 which is >on the "closing" side of the cycle, and I think that should be standard >on all high end DSLR's. 1/500 sync would be great; it would reduce the ambient softness when I use flash fill with long focal lengths. Signature<>>< ><<> ><<> <>>< ><<> <>>< <>>< ><<> John P Sheehy <JPS@no.komm> ><<> <>>< <>>< ><<> <>>< ><<> ><<> <>>< >For "noise reduction mode" for long exposures; yes. For normal >purposes, cameras may use blind pixel borders on the sensor. The 20D, [quoted text clipped - 4 lines] >contained in the RAW .cr2 file, and black is left with the offsets still >in them and in the exposed image (average is typically 128.2 to 128.4). That's fascinating information, John, thanks for passing it on. :) SignatureW . | ,. w , "Some people are alive only because \|/ \|/ it is illegal to kill them." Perna condita delenda est ---^----^--------------------------------------------------------------- |
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