Re: V35 Enlarger

["Gary Todoroff" <datamaster@humboldt1.com>]

WARNING: esoteric enlarger bulb tests results are about to be revealed -
viewer discretion is advised. . .

The new bulb arrived today for the V35 enlarger, so I did a comparison test
with the old bulb. Both are the Phillips 13139 as recommended by Leica. The
mirror finish on the new one definitely looked brighter. The results in the
enlarger were even more impressive.

To summarize:

                 Old bulb     New bulb   (magnification 9.5)

Lunasix  EV    7               7 2/3
 @f2.8

Focometer 
 seconds       3.8             .9
 @ f8

Method:

With the old bulb installed, I set the 40mm/2.8 Focotar to f2.8, turned on
the enlarger and adjusted the head to give me an EV needle reading of 7 on
my Lunasix lightmeter in incident mode (about 9 1/2X on the V35
magnification scale). I then stopped down to f8 and took a reading with my
Leitz Focometer (still with the old bulb). With the program setting
adjusted to my usual Ilford paper, the Focometer showed an exposure time of
3.8 seconds. Then I repeated the above with the new bulb in place, and got
the results as summarized above. All tests were done thru the empty 35mm
neg frame with no filtration. The Focometer readings were done thru the V35
white diffusion disk.

The new bulb is definitely brighter. The Focometer would seem to indicate
two stops difference!  In fact, when I stopped down from f8 to f16 with the
new bulb, the Focometer again indicated an exposure of 3.8 seconds.

I'm not sure why the Lunasix reading did not indicate as much difference.
The incident bulb on the light meter was about four inches closer to the
lens than the Focometer sensor. But it was at the same distance for both
bulbs.  

With the above findings, I now plan to record these baseline values of the
new bulb, and then measure them again every few months. However, it appears
that none of my old recorded exposures for prints will be accurate for
reprinting. I wonder how it will affect color filtration settings that I
have been using for Ilfochromes?

Hope this all helps someone to be careful with quartz halogen enlarger
bulbs.

Gary Todoroff