I am experiencing problems with inconsistent test strips (tests do not match the chosen time for the straight print, thereby rendering my tests almost useless). My equipment: Omega B-8 enlarger with an Aristo coldlight head (v54 lamp, I think! I purchased it from an individual who did not know himself and I can find no indication of which type lamp). Contrast tests performed with Kodak Polymax filter se; after the exposure time is decided upon (all strips with grade 2 filtration), I then test for contrast by exposing one strip at the chosen time for each whole grade number. All strips/straight prints are checked in white light after drydown. The coldlight head is a greenish blue light, more green than blue to me and was installed in 2002. I believe the v54 lamp is compatible with slot in filtration.
Sorry for length of this question, but as an example: Last night I tested for exposure at 3,6,9,12,15sec (I do not use times that may correspind to f/stops)---all at grade 2 at f/8. The best time was, oddly, 6 sec,. usually its in between. I then tested for contrast, hoping that the contrast strip for grade 2 at 6 sec would match the exposure test at grade 2 for 6 sec------not even close. In fact, I ran a test without a filter (for the hell of it!) for 6 sec. and it matched the grade 2 test for 6 sec----crazy! It is not fun when I can't rely on my tests. I've had my eye on a Durst M670 Variable Contrast Black and White Diffusion enlarger and am fixing to pull out my wallet if I can't get help.
Thanks for any responses.
You may be experiencing the drift that occurs in cold light heads. They can be quite unstable in their light output until the temp in the bulb is stabilized. If this is the case, I would switch the lamp on for several minutes before making any test strips determinations. If this is your problem that will go a long way to giving you more consistant light output.
In lieu of that Lee C. has worked out a closed loop system on his cold light head and it works to give him repeatable exposures. You may want to check with him on what he worked out.
I also have a Zone VI cold light stabilizer that would solve your problem too. I am not using it so I would be willing to sell it.
I agree with Don, it could be the colf light temp issue. I just leave the cold light on while preparing my chemicals in the trays. It works.
Thank you for the replies. I gather that it does not matter about the down time between processing prints. Once the temperature in the lamp is where it needs to be, then that down time, assuming it's not too long is not a problem? It can be 15 to 30 minutes to dry down and then viewing the tests------I assume that could be a problem and I should remember to turn on the lamp far enough in advance of the next exposure? I try to strive for consistency in everything that I do in the darkroom, so your comments are very helpful.
cold light heads do need to be warm to work. go figure.
Why not pop your test prints in the microwave to check dry down times? It will speed up your process.
If you take that long between prints it would be better to fire the cold light to allow it to re-warm just before you get ready to load the unexposed paper in the easel. The current Zone VI two color heads use this system and have a red and green light to indicate if it is ok to proceed or not. Try that for awhile and see if that fixes your issues.