Well the whole problem with this is that antialiasing filters defuse the image just before it hits the sensor. Defused light, by definition, is not parallel. I can think of no SLR WA lens with through the lens viewing that is not retrofocus anyway, or do you think you can put a non-retrofocus 15mm on a camera with a 45mm back focus and still focus on infinity?
The only reason I can think of to use a less than sharp as possible lens on a digital camera is you may not need an expensive antialiasing filter. A point for consumer P&S, but not for anything reasonably highend. Ciao, Graywolf http://pages.prodigy.net/graywolfphoto ----- Original Message ----- From: "Dag T" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Saturday, August 09, 2003 9:07 AM Subject: Re: Full frame DSLR and Film-Camera-Based Lenses > Well, I�ve got an M.Sc. in optics as well, and do a lot of work with > optics today, especially diffractive optical elements, and I don�t > agree with him :-) > > One thing missing from his discussion is the angular dependency of the > filters. They are most likely dielectric, and dielectric filters are > dependent on the angle of incidence of the light. I light falls from > an angle different from perpendicular the wrong colour will be filtered > out. > > Of course it is not necessary to have strictly parallel light rays, he > is right in that this would not make any images, but you do need "more > parallel" light rays than with film. Therefore some lenses, especially > wide angles, are not suitable for digital cameras. Micro lenses does > help a bit, but not enough. > > DagT > > P� l�rdag, 9. august 2003, kl. 04:50, skrev Mark Roberts: > > > 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. > > +++++ > > --- 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
