Regarding the compatibility of older wide-angle lenses with full-frame CCDs, this on the "red herring" of CCD illumination from optical supplier Sunix, Inc. at http://www.optics-online.com/literature/CCDlens.htm : "The light collection ability of all lenses falls off with increasing field of view. Relative illumination of a lens is defined as the ratio of light intensity at the maximum angle of view to that on-axis. For electronic imager sensors (CCD and CMOS), the off-axis brightness is further reduced by the collection efficiency of imager pixel structure. Many modern imagers use a micro-lens over each pixel to increase the fill-factor. The micro-lens will limit the field of view of the pixel. To be maximally compatible with the micro-lens field of view, the rays emerging from the lens must be within the acceptance angle of the micro-lens for all off-axis rays. This typically require that the primary lens be telecentric in imaging spacing. Non-telecentric lenses can also cause color and resolution cross-talk between adjacent pixels. This will further impair the off-axis performance of the imaging system."
Even if sufficient light reaches all of the CCD, the various wavelengths of that light must, of course, be carefully focused. In his survey of Nikon lenses, nature photographer Bjorn R�rslett commented: "The presence of colour fringing is in fact typical for most modern designs, since elimination of chromatic aberrations evidently is given fairly low priority. Hopefully, the coming digital era will alter the priorities here since digital cameras do need better chromatic correction than contemporary models." So, if the CCD must receive the various wave lengths of light focused as tightly as possible (something that may have been less of a priority in the decades before digital imaging--read Pentax SMC, M, A, F, FA--than it will become as we are dragged, even if kicking and screaming, into the digital era), we should ask: How close to apochromatic are various Pentax wide-angle lenses? If Pentax invested more effort than other manufacturers in correction of chromatic aberrations, the possibility of a full-frame sensor might be higher than if Pentax gave only average, or below average, priority to that aspect of lens design. Now, what if it isn't just that a given lens must work well with a CCD, but with a _particular_ CCD? Mr. R�rslett reports that a wide angle lens can perform differently even with CCDs of the same size: The 14mm ultra-wide angle lens Nikon designed to give real wide angle performance to a digital camera which includes an effective focal length multiplier (the 2.66 megapixel D1) produces increased color fringing with another CCD of the same 15.6 x 23.7mm size (in the 5.47 megapixel D1X). Oops. The Contax full-frame digital SLR works only with a new series of lenses which were designed specifically for the new range of (autofocus) cameras, which included the planned digital model from inception. The "counting teeth" scenario isn't relevant here: The question is whether existing Pentax wide-angle lenses will work with a full-frame CCD, not if lenses of a new design will work with a new Contax model. Perhaps the use of older wide angle lenses on a future full-frame sensor Nikon model will give us a hint, even if Pentax won't open up and say "Aaaah". - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
