Perry Pellechia wrote: >I guess the next question would be >how were these lenses designed. Were the shooting for 30mm and ended >up with a 31mm? I would have thought that they would have been >designed using some sort of computer system and the mathematics would >have been more precise. My guess would be the differences being >introduced by material changes (glass type and refractive index >changes, etc.)
Like everything else, lens design is a series of compromises. There are obviously size/weight/price/image-quality decisions to be made but my understanding is that even *within* the category of image quality there are compromises necessary. For example, designers can trade off high frequency contrast for low frequency contrast. They might also compromise barrel or pincushion distortion if they can improve sharpness or vice versa. (Which I think happened with the 43mm Limited - it doesn't bother me for my style of shooting but some people really object to the barrel distortion of the 43. I find its astonishing resolution of detail attractive and I rarely shoot scenes in which the distortion is visible.) Getting good bokeh may possibly involve trading off some sharpness. Even with computer design tools, these compromises are kind of like putting wallpaper on a wall and trying to get the air bubbles out: You push down on one spot and the bubble pops up somewhere else :) My guess that the designers of the Limited lenses placed getting to a specific, precise focal length much lower on their list of priorities than concerns about optical quality. They may have designed the 43 to come out at exactly that focal length, but I'd bet that they let the other focal lengths just fall close to the desired goal and concentrated on getting image quality where they wanted it. -- Mark Roberts Photography & Multimedia www.robertstech.com 412-687-2835 -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
