Re: [Rollei] Suplementary lenses, compound system from 100 to 200

[bigler@ens2m.fr]

> Uuhm, do you say that I need a -5 lens? I'm not good at mathematics
> you see. :-) /Patric

This is easier than converting a former European national currency
into an Euro ; and yes, I know, you don't care ( --only for the moment eh,
eh...-- ) in Sweden!!

The convergence of your 100mm lens is 10 dioptres. (1 metre = 1
dioptre, 0.5metre : 2 dioptres, etc...). You want a 200mm compound
lens = 5 dioptres. So I you just have to subtract: 10 - 5 = 5
dioptres. So you need a minus 5 dioptre supplementary lens = -200mm
negative lens.

This is the meaning of C = C1+C2 : I forgot to mention that C, C1 and
C2 can be expressed in dioptres and simply add to each other with the
proper sign, + for a positive lens, - for a negative lens.

Now if your additional lens is, say, a few cms in front of the
relevant principal plane H2, actually expect 6 dioptres instead of 5
to get a final convergence of 5 dioptres for the coumpound.

- -- 
Emmanuel BIGLER         
<bigler  

------------------------------