>> > Just curious - since all the light goes thru both the large lens and >> also >> > the smaller lens, does it matter which one is UD as long as >> one of them >> is? >> > Somebody who has better optics than I do? >> >> It does make a difference........ much like driving instructions - it >> matters a lot the order that you make your left and right turns!
>I was asking a serious question - in terms of distortions, the same amount >of light is passing thru glass, if my understanding is correct. Does the >cross sectional area make a difference? It was a serious answer from Dave, IMHO. In an typical optical system, every lens is different and plays a different role, so the change in total performance due to using UD glass in one lens if different depending on the particular lens that uses that kind of special glass. As the lenses are used to "bend" the light rays. I think that the driving example was quite adequate. If you bend more the light, you get more aberrations. I suppose that big lenses bend the light more than small ones. My 28-70 f/3.5-4.5 II uses an aspherical element for one of the small lenses. The 28-70 f/2.8 L uses an aspherical element for one of the big lenses. AFAIK the use of aspherical elements gives better performance when used in the big elements than in the small lenses. I suppose the same applies to UD and flourite. Best regards Vicente * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
