For some reason, these two statements don't jibe. Don't match. Like...one person is talking about one thing, and the other person drops a non-sequitur on the pile, and hopes for the best... <g>
Mike Johnston wrote: > > >There's no way they can get around it, except to make each new element > >match the previous elements very, very well, and test them together > >for final figuring. > Centering and collimation have nothing to do with the number of elements. > You can have a lens with many elements that has zero decentering and a > triplet that is badly decentered. > > --Mike Let's start over, sort of... Put a lens in the tube, and it's got a certain amount of spherical abberations and some coma. Change the material (to add color focus correction) and put an image-correcting lens in there, and you get rid of a lot of astigmatism, pinhole distortion, chromatic abberation and other stuff. But, you still have some sort of distortion. Granted, maybe only 5% of what you DID have, maybe clear out on the corners, but still... So, you add another correcting lens and SMC coat all of what you're working with. Look at it again. This time something else shows up. maybe some barrel distortion crept in, *I* don't know. Something... Add another lens to correct that. Eventually, you get a superior lens, and it performs beautifully! *That* is why you add lenses ~ to correct abberations or extend it's capabilities... So I see it, anyhow! And...we've not even mentioned centering or collimation problems. Where did that come from? Not me... That sort of thing belongs to the lens maker (grinder/polisher), so s/he doesn't introduce such... keith whaley
