No, Mark. You don't take the word of a guy who actually designs optics, you have to look on the web for an authoritive digital optics website produced by a dogcatcher, or a janitor. You are not even allowed to use your own common sense which would tell you the sensor in the hole theory is BS.
Ciao, Graywolf http://pages.prodigy.net/graywolfphoto ----- Original Message ----- From: "Mark Roberts" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, August 08, 2003 10:50 PM Subject: Re: Full frame DSLR and Film-Camera-Based Lenses > Richard Chu <[EMAIL PROTECTED]> wrote: > > >Olympus' brochures claim that the film-camera-based > >lenses would not provide good results with the CCD > >sensor because the light rays, especially at the > >edges, do not properly strike the sensor at an right > >angle. Does anyone know if images taken with Canon's > >full frame DSLR have any issues at the edges? If yes, > >if Pentax does come out with a full frame DSLR, > >wouldn't we need to buy new designed lenses to get the > >best results? If Olympus' claims are true, we should > >not count on using the existing lenses on a full frame > >DSLR if we want to match the results of the film > >cameras. The smaller CCD sensor in the *ist D is a > >compromise but it allows us to continue to use our > >existing lenses with good results. > > Here's a post from one-time PDML member Bill Peifer on this subject. > (He's PhD who works in optics in Rochester): > > All this talk about "analog" vs. "digital" lenses has got me wondering a > bit. I'm curious where this whole idea of CCD sensors requiring (or > preferring) perpendicular rays originated. I'm pretty convinced that it > must have originated because somewhere along the line, something got > taken > out of context, and a fundamentally incorrect idea grew from there. > From > the standpoint of the underlying physics, Tom is absolutely right -- the > purpose of a lens is to bring an image to critical focus at the focal > plane, > and the nature of the sensor (film, CCD, CMOS, or other) isn't > particularly > relevant. After all, if all the light rays strike the sensor > perpendicularly, then they are necessarily parallel and thus cannot form > an > image at the focal plane! > > I suspect that this perpendicular-ray story -- dare I say "legend"? -- > may > have originated from a misinterpretation of the characteristic behavior > of > CCD sensors. We all know that in single-chip color CCD sensors, some of > the > pixels are sensitive to red, others to green, and still others to blue. > For > the case of color cameras with single CCD sensors, color sensitivity is > imparted to a particular pixel by incorporating a microscopic optic -- a > lenslet and filter -- in front of that pixel, which I believe is > accomplished as part of the manufacturing process for the sensor chip. > I > can imagine that the numerical aperture of this microscopic optic may > not be > terribly large, and it might very well constrain the field of view of > its > corresponding pixel. Maybe someone that knows more about chip fab can > comment on this. Anyway, although each individual pixel may very well > be > "looking" through an optic with small numerical aperture, it's only > "looking" a very short distance (microns? tenths of microns?) to the > illuminated spot on the focal plane directly in front of it. In fact, > this > is precisely what you want. If each pixel had a more "wide-angle" view, > it > would not only register the intensity of light directly in front of it, > but > it would also register the intensity of light from a immediately > adjacent > pixels (perhaps pixels intended to sense a different color), resulting > in a > spatially and chromatically degraded image. The characteristics of the > macroscopic, "analog" lens mounted onto the front of the camera -- focal > length, f-number, etc. -- isn't particularly relevant, except that a > faster > "analog" lens will make each pixel-size spot of light at the focal plane > correspondingly brighter. > > Jaume's original question about spectral characteristics of particular > lenses and lens coatings is interesting as well. The general strategy > in > designing the ~lens~ is, among other things, to reduce chromatic > aberration; > that is, to get red, green, and blue rays from a single object point to > focus at a single point on the same focal plane. I think lens > ~coatings~ > are generally optimized to match the response of the human eye, rather > than > the film emulsion. (Likewise, most film emulsions -- excluding > infrared, of > course -- are designed to match the human eye.) I believe that the > general > strategy in designing antireflection coatings (like SMC) is to minimize > the > reflective loss of green light, since green is the color our eyes are > most > sensitive to. This doesn't mean that the coated lens passes primarily > green > light; rather, it means that for the 1% or 2% of light that would > otherwise > be lost at each air-glass interface of an uncoated lens element, the > lens > designers try to "rescue" the green component by applying a > green-optimized > antireflection coating. CCDs are more sensitive to the red end of the > spectrum than the human eye. You might imagine that in order to > maximize > the signal level at the focal plane of the CCD, a lens designer might > consider using antireflection coatings optimized for passing red light. > However, this would yield an image with what we would perceive as a > highly > perturbed color balance. In fact, for consumer imaging applications, > designers use filters that ~decrease~ the intensity of far red and near > infrared light impinging on the sensor. Thus, I can't imagine that > consumer > digital camera designers would go to the expense of new lens designs, or > bodies specific for old vs. new lenses. (Although that would certainly > be > an interesting marketing gimmick....) > > Just as a final aside, I'll mention a pet peeve of mine. It seems that > in > many discussions, we refer to film-based and CCD-based imaging as > "analog" > and "digital". This is really an artificial distinction. CCDs, after > all, > ~are~ analog sensors, and the readout electronics for CCDs are analog > circuits. The only thing that makes "digital" cameras digital is the > way > the analog signal array is stored after being read off the CCD sensor. > A > minor point, but a pet peeve nonetheless. > > -- > Mark Roberts > Photography and writing > www.robertstech.com > --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.507 / Virus Database: 304 - Release Date: 8/4/03
