On Aug 25, 2006, at 2:57 PM, Toralf Lund wrote: > Graywolf seemed to suggest that the lens designers are (were) in fact > doing this already on "traditional" SLR wide-angles, and that it would > be hard to correct the rays even further...
The traditional inverted telephoto designs required for very short focal length lenses on SLRs help in this regard but are often still not optimal for a digital sensor. Digital sensors require much more care in designing the light path at the edges of the frame compared to film. Traditional IT ultrawides were primarily designed to allow the mirror to clear the back of the lens, not to straighten the light path for a digital sensor. Many work reasonably well on the 16x24mm sensor format, but lenses designed and tuned specifically for the digital sensor typically show modest improvements at least. The '1.5x crop' sensor format was chosen as a reasonable compromise for an existing 35mm film lens line precisely because it gives a reasonable chance for an lens designed for film capture to operate well within the constraints and sensitivities of a digital sensor (aside from the fact that a sensor with 60% area is much less expensive to manufacture...). BTW: A 'designed for digital' lens mount, like the 4/3 system lens mount, has a shorter register and a wider mount diameter relative to the sensor format to allow additional light path correcting elements at the rear of the lens, situated closer to the focal plane and also to allow the sensor to be more centrally located relative to the lens. The only such mount is the 4/3 mount... note that it has a mouth as large or larger than the Canon EOS mount (which has the largest diameter from the 35mm SLR camera world) and a shorter mount register (38.67 mm vs EOS 44.00 mm or K-mount 45.46mm). The shorter register and wider diameter allows more freedom in making lens designs that work well on a digital sensor. Godfrey -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
