[pure-silver] Re: Durst L1200 (condensor) & uneven illumination
- From: Georges Giralt <georges.giralt@xxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 03 Aug 2007 19:48:59 +0200
Hi !
So, as Cor asked, I've made some more experiments.
I tried to measure light evenness on my Laborator 1000 baseplate without
lens but, even at the highest column position, the Analyser Pro keep
saying "HI". I'll try to find a less powerful bulb and see where we stand.
With the Nikon EL 135mm F:5.6, head at top of column, I've to stop down
to F:11 to get a reading different of "HI". The enlarger's condenser
system being set up for 4x5 printing. The measurements were made as follow :
First, measure at the center of the baseboard to get the 0.0 density
reading, next one measure of each corner starting with the front left,
front right, rear right, and rear left. They are numbered 1, 2, 3 and 4.
Of course, you've to return the Analyser Pro to normal mode every time
you change aperture, in order to get the 0.0 reading.
Results :
F:11 0.11 0.11 0.11 0.09
F:16 0.10 0.10 0.10 0.10
F:22 0.11 0.10 0.10 0.09
F:32 0.11 0.10 0.10 0.10
F:45 0.13 0.13 0.13 0.13
Results are damn consistent, and I'm _really_ surprised to have no light
falloff due to lens F stop. So I made another set of measurements, this
time at the middle of each corners, in the same order than above :
Results :
F:11 0.08 0.04 0.08 0.08
F:16 0.07 0.05 0.06 0.06
F:22 0.06 0.04 0.08 0.07
F:32 0.07 0.04 0.07 0.08
F:45 0.09 0.03 0.07 0.08
Here, there is one side which is consistently brighter than its
neighbors, so maybe there is a little mis-centering of the bulb in its
box. But, as these figures are so low, I'll let this setup untouched ....
Of course, I had removed the thick frosted glass and tracing paper from
the filter drawer, and this is good news ! Because I had to endure
sooooo looong printing times with the previous setup.
I wonder how I made the measurements which leaded me to instal the
frosted glass and the tracing paper into the filter drawer ? Maybe a bad
bulb or an improperly installed bulb ? Or could it be the lens which was
at fault ? (I do not remember with which one I had made the
measurements, but sure it was not the Nikon as I bought it new a few
month ago....) So I now have to make measurements with the enlarger set
up for 6x6 negs and 24x36 negs. And, test the other lenses I own, who
knows, maybe will I sell some of them ?
Thanks for reading so far ! and enjoy your week end !
Lloyd Erlick a écrit :
At 10:25 AM 7/29/2007 , Georges wrote:
...
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
...
July 30, 2007, from Lloyd Erlick,
I'm no expret in this, but I think those figures indicate pretty good
evenness.
If I'm wrong I'd love to hear the dissertation...
regards,
--le
________________________________
Lloyd Erlick Portraits, Toronto.
website: www.heylloyd.com
telephone: 416-686-0326
email: portrait@xxxxxxxxxxxx
________________________________
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