[pure-silver] Re: Durst L1200 (condensor) & uneven illumination

Hi Georges,

So it seems you observe the same phenomena than! If you raise the head of the 
enlarger, or use some good ND filter, can you also measure at the widest 
aperture? If it is mainly the lens that is causing the problem, you should 
measure more light fall-off

Besr,

Cor


-----Original Message-----
From: pure-silver-bounce@xxxxxxxxxxxxx on behalf of Georges Giralt
Sent: Sun 29/07/2007 16:25
To: pure-silver@xxxxxxxxxxxxx
Subject: [pure-silver] Re: Durst L1200 (condensor) & uneven illumination
 
C.Breukel@xxxxxxx a écrit :
> Thanks for all replies on my question!
> 
> Last night I indeed confirmed that the "uneven illumination" was
> (mostly) due to light fall-off of the lens: when stopping down from f11
> to f4 (fully open) the light-fall off in the corners was increased by 1
> to 1 1/2 stops, as predicted by the graphs..
> 
> So it's nice to get some peace of mind..;-)..that it's largly a inherent
> quality of the enlarger lens, and not so much the illumination of the
> enlarger,
> 
> Thanks again & best!
> 
> Cor
Hi !
So I had a few minutes to test my Durst Laborator 1000 with condenser 
with the Nikon EL 135 F/5.6. I removed the frosted glass and drafting 
paper  had in the filter drawer, making the enlarger really brighter.
I was obliged to close down to F:32 in order to be able to use the RH 
Designs Analyser Pro without saturation.
At F:32, light fall off is at 0.11 to 0.14 depending to what corner you 
measure. These are relative from the center which, obviously reads 0.0.
At F:45 the figures even out at 0.09 to 0.11.
So I think I'll stick to this, and use the enlarger without frosted 
glass, and gain that extra stop f light I enjoy with the slow Foma or 
Forte papers....
Hope this helps !
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