Re: [Leica] Noctilux and filters

["Joe B." <joe-b@dircon.co.uk>]

At 13:12 23/01/00 -0500, you wrote:
>Joe:
>
>Infrared light focuses at a different plane than visible light.  There is an
>"R" on many lenses that marks the approximate infrared focus point.  You
>focus as normal and then you are supposed to move the distance on the scale
>from the arrow to the "R".

Hi- yes, I know- but I was using infrared Ektachrome.

>   I don't know if the Noctilux has this.

Leica lenses nowadays don't have ir focusing indexes- the explanation they 
gave according to Osterloh is that since the index would only apply to one 
focusing distance and would be off at others, it would be misleading.

>   I assume
>this is for B&W infrared with the black filter.  Since most people shoot the
>IR Ektachrome with a yellow or green filter a lot of visible light mixes in
>with the infrared.

An infrared Ektachrome image shot with a filter you can see through 
(yellow, orange, etc) is mostly made by visible light! Only a small portion 
of it is actually made from infrared radiation. That is why the lens is 
typically focused normally with this film.

>   Still the focus shift may explain the out of focus shots
>at F-1
>
>Mike D

I might set up a test at some point to see if I can find a focusing shift 
with filters, caused by the filter itself, on the Noctilux. This really 
wouldn't be an issue except that I really like the strange look of infrared 
Ektachrome through this lens. It would be nice to know for sure.



Joe B.