Archived posting to the Leica Users Group, 1996/01/22
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]
On 21 Jan 96 at 23:40, Albert Yeh wrote about "Infrared":
> To all:
>
> How can you use Leica non-Apo lens to deal with the infrared
> film?
>
There is probably a red dot on the DOF scale of your lens, you have
to adjust focus to that point after normal focussing. Depending on
the lens, it can vary from f5.6 to f11.
Don't go easy by just closing down aperture to overcome the
focussing problem: diffraction (the bending of light rays around the
aperture blades) is twice as worse with IR as with visible light,
since this phenomena also depends on wave length! Try to stay
withing two-three stops from maximum aperture.
There are a few other methods and procedures to correct focus, but
the red dot is the most convenient.
BTW, this apo stuff is the main reason for me to be interested in
those Leica-EOS adaptors: although not cheap, the 3.4/180 APO is a
good solution for the focussing problem I have with my EOS
2.8/200....but an EOS 1.8/200 would perhaps be even more fun, and for the
same price....;-))
(does anyone know if the new Leica 70-180/2.8 APO can do without
focussing correction? Most APO zooms of other brands can not....but I
guess Leica knows very well *when* to put 'APO' on a lens....:-))
Bye,
_/ _/ _/_/_/_/_/ _/_/_/_/_/
_/ _/ _/ _/ _/ _/ _/
_/ _/ illem _/ _/ an _/ _/ _/ arkerink
_/_/_/
<w.j.markerink@a1.nl>