Printable View
I was wondering what kind of filtration I might need for B&W papers when using a fluorescent light source in the elarger. I realize that a murcury v apour source is the norm for a cold light, but at the moment I can't fork out th e money for an Aristo cold light. I have an 8x10 enlarger. thanks
Colin, If your light source exposes the paper in a reasonable time without unevenness you are in business and shouldn'r require any special filtration. The only problems I would anticipate with a homemade flourescent source are possible uneven coverage, depending on tube positioning and diffusion, and possible long exposure times if your source does not contain enough of the needed blue/green end of the spectrum or is too weak. Commercial cold light heads are quite bright and deliver a high concentration of the color neede to expose the paper. Graded B&W papers have a limited sensitivity and in essence "take what they want" from the light. With variable contrast B&W you will have to experiment. VC papers contain two emulsions, one sensitive to bluer light and one sensitive to greener light. Depending on the exact spectral composition of your flourescent source, the VC filters will deliver more or less of each in comparison to the manufacturers standard light source, which is probably not the same (it's usually incandescent). Therefore, your "grades" will vary from theirs, but will probably be quite useable. Once you get used to your setup, there should be no problem. If the contrast grades on either end are not extreme enough, you might try various magenta and yellow filters and see if it makes a difference. (I assume you are not interested in printing color since flourescent light sources don't deliver the continuous spectrum necessary for color work.) Good luck with your project! ;^D)
A word of warning about flourescent lights. When a flourescent light is turned off, it continues to emit a small amount of pulsating light, creating opportunities for fogging. Additionally, since they pulsate when illuminated, short exposure results would be difficult to repeat, since the actual light duration will vary.
Otherwise, your variable contrast filters will work, but not the same way as they will under an incandescent light source due to the difference in wavelength.A #3 filter will not really be a number #3 under the flourescent source - it may be a full grade or more off - I would experiment extensively after you get the enlarger working.
There was an excellent article in View Camera Magazine a few months ago on the subject of a new way of systematic printing. One of the changes involves the use of a metronome rather than a conventional timer to count off the time. You turn on the enlarger while holding a piece of cardboard below the lens. The enlarger light has a chance to warm up and stabilize. Then you withdraw the cardboard and counts off the time. When the time ends you cover up the light with the cardboard once again, and then turn off the enlarger.
I've been using this method (& the rest of his plan) for about six months and this technique has made consistent exposures much easier for me than before and I would think that it would be even more important with a flourescent light source.
I should point out that the metronome timer method is only one part of the author's printing method and a read of the article will fill you in on the rest.