Quote:
Originally Posted by Wavytone
The issues of focusing, zooming, weight and variable aperture have no bearing on the lens design.
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You are quite wrong. Issues of focusing, weight, image stabilization and variable aperture have a
DIRECT BEARING on lens design.
I'm happy to take this in another thread as it has nothing to do with original posting, but I have designed quite a few telescopes based on lens, mirror and compound varieties and know well what can and cannot be done. For example, most telescopes do not move any part of their optics during focus (they move sensor), or if they do (like in SCT for example) they move just about the heaviest part. Telephotos have to be designed with having a cardinal plane defined where beam is narrow (so any active elements like focusing group, image stabilization group or stop down mechanism - iris - can be small in order to be able to move
fast). Also, telephotos must reduce the beam as quickly as possible after entering for the same reason, so all subsequent potentially very expensive elements that are extreme dispersion glass, Fluorite and/or aspheric, can also be small and cheap. Telescopes do not have to do any of that. So we have designs like Busack/Riccardi/Wiedemann/Honders that are better corrected over larger area than those super-telephotos, and are as fast (or faster), that is have lower f/number (some can be pushed to f/2 or faster) and do not require 10 elements. But they cannot do IS, cannot quickly stop down and cannot do autofocus 20 times a second.
Trust me, if we were allowed to use same/similar size elements in a modern telephoto lens, their performance could be vastly improved without having to resort to 10+ elements. Heck, I can design a Petzval with just about 5 or so lenses at f/4 that will leave any 600/4 L (or Nikon ED) in the dust. But all lenses in it would be large and heavy, so no IS, no quick AF, body would have to be much longer and much heavier, and finally it would be a lot more
expensive with several full size elements out of FPL glass or Fluorite, and others from just little bit cheaper Lanthanum glass).
Do you think it would sell?