Archived posting to the Leica Users Group, 2003/05/07
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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