Archived posting to the Leica Users Group, 2003/05/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Don Nah! We're not talking 'bout the differences 'tween a retrofocus design vs. a normal or telephoto design. The aspheric designs don't introduce a negative element to change the apparent "cone angle". Your second contention may have merit though. I wish that Richard Knoppow were on this list. Jerry Don Dory wrote: > Jerry, > The answer is in two main areas. The first is; consider the cone of light > coming off the last element. If the cone has a very large angle then the > circle of confusion will expand very rapidly from the point of focus. This > is easy to visualize, just roll up a piece of paper in a very tall cone and > then a very broad cone. So, if the optical design uses the last element for > a major change in the light path then you could have a fairly shallow plane > of focus wide open. Obviously, as you stop down, this effect will diminish. > > The second area is a little more esoteric. As a lens designer, if all you > care about is what the light looks like at the plane of focus, then you > could allow aberrations to exist outside the plane of focus. I think this > is what is going on with the aspheric elements, you design to the plane of > focus and if the light bundle does interesting things before or after then > who cares. > > 0.02 > > Don > dorysrus@mindspring.com > > -- > To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html