I have reciently got my hands on an MPP Micromatic 5x7 enlarger. However, the bulk of my experience is with a condenser based enlarger, and the Micromatic is cold cathode based. How do I use it, does the light need to 'warm up' before use do I need to keep the light on and use a shutter to expose prints? Please excuse my stupid questions as I am new to cold light enlargers. Also, is there anything I need do when using VC paper?

Thanks

-- David Kirk (david_j_kirk@hotmail.com), November 28, 2000

Answers

David I don't use cold cathode myself but an old acquanintance used to use one in his profession on the DeVere 504 and he left it on all the time during a print run for he said it needed a warm up time to reach the correct light output. I'm sure someone out there could confirm or deny this. Regards,

-- Trevor Crone (tcrone@gm.dreamcast.com), November 28, 2000.

I've heard and experienced conflicting points of view. The light ouput of cold lights is supposed to gradually increase and then decrease beyond a point. I've heard of a Horowitz compensating timer that is supposeed to compensate for this by measuring the actual light emitted - you should check with Calumet regarding this (they might carry a Zone VI version). I've lived with it because I never noticed the problem. With most normal exposures and times between exposures (what with changing the negative etc), there is enough time for the head to cool down again. If you're doing batch processing and making multiple prints from the same negative, you might want to consciously leave time between exposures to let it cool down.

Regarding cold lights and VC papers, the filters for VC papers were designed for tungsten sources. Cold lights, especially the older W45 and W55 versions are a lot more blue heavy and will result in higher contrast prints. Thus, a print made through a supposedly grade 2 filter will exhibit higher constrast i.e., it will accomodate an underdeveloped rather than a normally developed neg. Recalibrating is remarkably easy - get a step wedge and print through the filters to get the contrasts. Be prepared for unequal contrast specing (I found little or no difference between filter 4 and 5 and quite a bit between 0 and 00). Another problem is that you may not get extremely low contrast - a good solution to that is to use Howard Bond's solution - a 40CC yellow in addition to the regular filter. Joe Englander prefers a green filter. Good luck. DJ

-- N Dhananjay (ndhanu@umich.edu), November 28, 2000.

Hi David. You need to let the Cold cathode warm up for about 10 mins before you use it. Then you can either leave it on and use a bit of black card to regulate the exposure, or you can use it normally with a timer or footswitch or whatever, as long as it's only off for a short length of time. The light output is temperature dependant, and once the tube is warm, then the light is fairly constant.
As the previous post said, you'll have to calibrate the enlarger for VC filtering. It might also be worth taking the cold-cathode assembly apart to clean it. The high voltage attracts a lot of dust to the tube, and this can reduce the light output quite badly.

-- Pete Andrews (p.l.andrews@bham.ac.uk), November 29, 2000.