[filmscanners] RE: Newish Digital Tech
>...but why would a PMT > get more > > light, > In semiconductor sensors, however, many, perhaps most, of the > photons that hit the junction do absolutely nothing, so they're much less > sensitive. Hi Paul, Id believe that PMTs have a much lower noise floor than CCDs and that is the reason for the much higher dynamic range, and obviously better shadow detail. Is that what you are talking about? As far CCD sensitivity...CCDs have a minimum number of photons before they can register, but I believe that once that level is reached, most of the photons that hit the sensing area are being counted (accumulated)...I don t believe they are doing nothing? Regards, Austin Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] RE: Newish Digital Tech
> From: Austin Franklin > > My second statement is based on images Ive seen like this: > > http://www.pbase.com/image/10390721 That image looks totally strange, unlike any of the other images in the set, so I have no idea why it looks as it does. However, this one: http://www.pbase.com/image/10906254 is exactly the sort of image that would be _much_ noisier on my DiMage 7. I have no experience with high-end digicams, though. -- Ciao, Paul D. DeRocco Paulmailto:[EMAIL PROTECTED] Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] RE: Newish Digital Tech
> From: Austin Franklin > > What about the sensor layers below the top one, and then below > that? There must be some decrease in transmission (not just due > to the top filter, but due to the sensor, material whatever...). > All the Bayer sensors measure %100 of the light that particular > sensor is filtered for, where the Foveon gets decreased light > to the inner two sensing areas. The principle is that the top layer only absorbs red light, converting it to an electrical signal, and passes the green and blue unattenuated. The second layer absorbs the green, converting it to electricity, an passes the blue, which is absorbed and converted by the third layer. > Given this (and a few other issues that relate, like accuracy of > sensing the frequency), I would speculate that the Bayer pattern > sensor would have higher color fidelity (with respect to accuracy > of color) than the Foveon. If you think about how the eye works, what's important in an RGB sensor is that each color filter have a sloped spectral response that overlaps the adjacent color filters, and that the peaks of each response line up with the peaks of the eye's response. This guarantees that any perfectly saturated color of light (e.g., laser light of any visible wavelength), will produce a different weighting of the three outputs. In the X3 chip, the skirts of the filters are more gradual than in conventional chips, but this is something that can be compensated for accurately using arithmetic after the fact. > Also, this issue about %100 of the light keeps being stated by most > everyone who champions the Foveon. Even if it were true, its > a matter of > significance. I do not believe it is a significant issue at all. People > can claim it is, but no one has yet to make any sense as to why, or shoe > evidence of it being so. The low light performance of the Foveon is not > very good, in fact. I believe if it is an issue at all, it is a > VERY minor issue. All other things being equal (which they're not, yet), it could prove to be a major advantage. As I said in another post, my $350 2MP Digital Elph has less noise than the 5MP DiMage 7 I paid $1300 for. The full frame high-end digicams have lower noise still, all because the pixel sensors are bigger. -- Ciao, Paul D. DeRocco Paulmailto:[EMAIL PROTECTED] Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] RE: Re:Re: digital artifacting
> Been there, done that. My 8000 scanner blows away anything I > get out of my digital SLRs. That includes a D60, and an S2. > > > Best Regards, > > Tim Schooler That's discouraging. Over the last couple years, I've scanned about ten thousand slides with my Polaroid SprintScan 4000 at 4000 dpi, and I've had it up to here with the workflow, and have been eagerly watching the progress of digital SLRs. I can't WAIT until I can get away from this scanning business! But it looks like with my budget, it's at least two to three years away, and I ain't getting any younger. Frank Paris [EMAIL PROTECTED] Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
[filmscanners] RE: Newish Digital Tech
>-Original Message- >From: [EMAIL PROTECTED] >> >Hum. Do you have a source for that? I dont believe that is >> >true, and will >> >have to think about your assertion. What is the source of the random >> >variations? I know there is some randomness in reception of photons, >> >simply because of atmospheric dispersion, and other causes... >> >> I think he is talking about the quantum noise which is introduced >> due to the >> Poisson probability distribution of the Photons hitting the detector. The >> resulting error in the signal is proportional to sqrt(2). > >Hello Robert, > >If he is, thats called shot noise and its = sqrt(S), where S is the >signal in electrons. It certainly is the noise that limits CCD >performance. Yep, shot noise = photon noise. And yes it's sqrt(S). So when the signal is twice as big then the noise only increases by sqrt(2) which improves the SNR. Robert Unsubscribe by mail to [EMAIL PROTECTED], with 'unsubscribe filmscanners' or 'unsubscribe filmscanners_digest' (as appropriate) in the message title or body
