Enlarger condenser illumination problem - part 2
So based on some good tips in the forum and some helpful information from Ian C, I've discovered it is actually the bulb that is creating most of the problem (distinct hot spot and irregular concentric circles). The tip of the bulb facing the condensers has exactly this pattern in the frosting. This of course does not really address the falloff issues, but first I need to tackle the bulb itself. First let me say although I understood condensers project collimated light, I did not realize how "in focus" the bulb is.
I have a bunch of replacement bulbs I had ordered for my Omega B66 a while back. They are all 75W bulbs made by Eiko, which seems to be the only brand around for some reason. They are the proper spec for this enlarger: PH/140 - 2,900K. So here is the problem. They all have this crap frosting job so no matter which one I try I still get patterns and distinct hot/cold spots, although each bulb is obviously slightly different.
First question: Does anyone make higher quality enlarger bulbs like this that have even frosting, as opposed to these junk Eiko things?
In an effort to solve the problem, I bought a variety of bulbs at the hardware supply - various shapes and sizes (all small enough to fit in the condenser head above the heat absorbing glass), all frosted:
Problem #1: The highest wattage I can find for bulbs that fit, is 60W. Can't find 75W. = even longer exposure times than my already long exposure times
Problem #2: The one that works best (has very smooth, even frosting, so no flaws projected), is a small globe-shape which therefore sits higher in the head than the recommended PH/140. It doesn't extend as far down toward the heat absorbing glass. This further reduces the effective output of the already weak 60W. By measuring the center of the projected light on the baseboard with my spot meter, I am losing nearly two stops versus the Eiko bulb. However there is an upside - the fact the bulb is higher above the condensers seems (logically) to reduce the amount of falloff toward the edges and corners. So while the overall illumination level is much lower, it is more even.
Problem #3: Not sure if this is problem but need advice - the various bulbs I bought at the hardware supply, while all "white" are obviously different in color temperature. The small globe I refer to in problem #2 is quite warm compared with the EIko (designated 2,900K). So - for black and white enlarging onto variable contrast paper with multicontrast filters, is the color temperature important? Is it necessary to use only 2,900K bulbs? Even though the light ends up going through a contrast filter, does the color temperature affect contrast? Since VC paper is sensitive to blue and green, does a warmer white light bulb (ie more red in it) affect contrast, or simply increase exposure time?
Please address all the questions. Need help here. I guess ideally someone will be able to point me to a better quality PH/140 2,900K bulb and then the rest of the questions become moot.
The bulb you want isn't 'frosted', its 'opal'. It should look solid white, like it was filled with white paint. If it looks frosted, like an ordinary household bulb, then it is the wrong sort.
These people seem to imply they sell the genuine GE article, but I suppose they are as likely as anyone to give you a Wiko/Delta/Eiko or some other strange Chinese substitute. Call them up and see.
First, where are you? Sure is handy if people would provide that info in their profile.
If you are in the States, the PH140's I get are GE and/or Slyvania -- bought from Bulbman. I usually buy them by the case. Seem to work fine -- no problem with the frosting as you indicated with the Elko.
I think one of the differences you will see between the hardware store bulbs and the PH140's is consistancy of output, and bulb life when turned on and off repeatably.
At least with LF landscape, a bad day of photography can still be a good day of exercise.
Thanks to both of you for the help! I'm in Montreal, Canada by the way. Montreal is THE most pathetic metropolis on earth when it comes to buying darkroom equipment/supplies - there is literally nothing here. I order all my stuff from the states anyway (usually from B&H in NYC but I think they only had Eiko bulbs) so I'll gladly give both the links a try.
Maybe take a look at KHB in Mississauga, ONT.
They list a lot of enlarger stuff, including lamps.
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