Bessler 23C II Condenser "Warm Up" Issue

Discussion in 'Black and White' started by dmcca, May 16, 2020.

  1. I have an issue where my enlarger has to warm up for a few seconds to be in focus. This make no sense to me... even if the bulb needed to warm up, how would that affect the focus?

    I have an Eiko PH140 bulb in there and have the same issue when I bypass the timer. I was also thinking it could just be my eye readjusting... but it's not.

    It takes 2 to 3 seconds for the grain to come in focus after a few minutes of not being used. I'm printing a lot of 8x10s from 35mm negs and with my lens stopped all the way down my full exposure time can be as quick as 1.6 seconds. I've taken to covering up the whole sheet of paper and running the lamp a few seconds before each print and test strip... but that seems absurd.

    I can't seem to come up with anything trying to google this problem... anyone with condenser experience run into something similar?
  2. ericphelps likes this.
  3. AJG


    Condenser enlarges are notorious for causing negatives to pop due to excessive heat, so your practice of covering the paper in the easel is probably the way to go unless you get some effective heat absorbing glass. Alternatively, you could look into a cold light which uses fluorescent tubes instead of incandescent bulbs. The heat from the light source is lower so negatives don't pop, but fluorescent bulbs also take some time to reach maximum output. I have used a cold light for a long time and dealt with the varying output by using a Zone VI timer that reads light output directly inside the lamp house and adjusts time intervals automatically to compensate for varying light output. This works extremely well and it is easy to make 20 identically exposed prints one after another.
  4. Conrad's writeup is great. In particular you are looking for the part titled "The Enlarger Optical System" which discusses negative "pop."

    It occurs to me that both he and AJG explain about the heat with the assumption that you understand something about incandescent lamps and infrared "light," which maybe you do or maybe you don't. Of course a "heat-absorbing glass" is the simple answer in either case, but if you want to understand a bit better, I'll try to give a long-winded explanation.

    An incandescent lamp, the sort that can burn your fingers, makes light by heating a filament until it glows brightly. When you began to heat something, anything, it begins to give off a sort of "light" that we can't see, called infrared "light." (You've probably seen thermal images on the TV news or commercials, where they show how warm a person's face or body is via different artificial colors.)

    Anyway, as an object is heated up more and more it eventually begins to give off a reddish light. But the great majority of the "light" is infrared. Heating even more, so that greenish and bluish light are also given off, gives a white light, albeit more reddish/yellowish. We would ideally like it to be as white as the sun's light is, but our filaments would have melted long before that happens. Anyway, the huge majority of "light," or better described as radiation, is the infrared which we can't see. Photographic films and papers can't "see" it either, for the most part. But the infrared CAN heat things up.

    When the central part of the negative is heated up, whether due to visible or infrared light, it tries to expand. But the outer edges, being protected from the light, don't expand. So the central part of the film can only expand by bulging out in the general manner of a plastic sunglass lens. Thus the negative can go out of focus, depending on how warm it gets. Now, regular light also causes this heating-up, but the infrared radiation from an incandescent lamp is much greater, as a very wild guess possibly on the order of 5 or 10 times more. So, the obvious fix is to prevent the infrared light from reaching the negative. And this is exactly what the heat-absorbing filter does - it blocks infrared light. The filter gets hot instead of the film.

    You don't have this problem with a so-called cold light as they have a different way of producing light. These include fluorescent lamps, as well as LEDs. They aren't producing large amounts of infrared radiation, so they can be much cooler.

    As a note I've spent years working in high-volume photofinishing. The standard sort of printing machine there could expose a color 8x10 inch print in less than a half second. Including paper advance, twenty 8x10s could be exposed in perhaps a half-minute or so. These machines used high-wattage incandescent lamps, tungsten halogens, but using a different method to control infrared light. Instead of a heat-absorbing glass they use what are known as dichroic filters; instead of absorbing radiation they can reflect or transmit it. A tungsten-halogen lamp can have a small, efficient dichroic-filter reflector around it that only reflects visible light; the unwanted infrared can "leak" out the back of the reflector. So the innards of the printing system never "see" the infrared "light." Another method is to put a so-called "hot mirror" in the light path; this mirror is designed to reflect the infrared. Anyway, these were some long-time industry methods to deal with such issues, way before the advent of digital exposures via lasers or LEDs. But enough history... just look for a heat-absorbing glass filter. Or, keep your negs pre-popped, as you are doing now.
    Last edited: May 16, 2020
  5. Black and white negative, due to their metallic silver image, absorb infrared light. The infrared radiation is thus converted to heat. This heat causes the multi-layered film to change demotions (expand), this causes the pop that changes the lens to negative distance and thus the focus. Color negatives, void of silver will also "pop" but the rate of their expansion is not as great. Heat absorbing glass called a "cold mirror" works best. Install a cold mirror, reflection side facing the lamp. This will lessen the pop.
  6. Is there a good source of cold mirrors? Last time I looked for something big enough, maybe 6"x6", the cost was outrageous. Thus my use of the much poorer factory filter.
  7. Just use a LED bulb. Problem solved.
    BTW, I suspect some diffusion heat glass (some sold as original enlarger accessories) are just thick green cheap glass at outrageous prices. I have some of them (Beseler, Durst) and cannot see anything "special" on them but just a simple barrier. I may be wrong.
    Last edited: May 19, 2020
    rodeo_joe|1 likes this.
  8. Definitely look into an LED replacement for the enlarger lamp.
    Chances are it will be less bright - thus solving your short exposure times - and run much cooler.

    I can't agree about heat-absorbing glass just being 'green' window glass though. Special IR blocking glass does have a slight cyan tint to it, but ever since the invention of dichroic coatings, the way to block heat has been to use glass coated with an IR reflective film. This has no colour, and is usually quite thin, since it reflects, not absorbs the heat.

    However, energy has to go somewhere, and heat absorbing glass gets very hot and needs a heat-sink mounting or surround. While reflected heat goes back into the lamp-housing and any intervening condensers; possibly reducing the life of the bulb.

    So, yes, LEDs are definitely the best solution, and will work with a condenser system. 'Cold light' needs an entire new head and high-voltage transformer. It also changes the printing characteristics of the enlarger. Also, the output of a used or old cold-cathode tube may well be lower than when new, and replacements are neither cheap nor easy to come by.
  9. The main issue with LED is, as Rodeo says, lower brightness.
    But if you print "normal" sizes, say 8x10, it could be not a problem at all. If you print really large, you may need to use a powerful tungsten bulb.
    Also, I think many people use to print with too much brightness, hence briefer times. It could be good for fast, massive printing, but not "serious" printing, where you need longer times for burning and dodging techniques. I never print less than 10 seconds.
    Right now there are really powerful LED bulbs (15, 20 watts), the problem is size. You need a bulb that fit the lamp housing, unless you made a custom sized housing.Brighter bulbs are usually larger.
  10. Another option . . . I have to go look at my 23C (it's not in current use) but where do you have the upper bellows set? I never set it at "35mm" as I found the light too bright, printing times too shot and the light a little harsh. I always moved it to the top even when printing smaller negatives. This would have the added benefit of lowering the heat at the negative stage.
  11. The standard tungsten bulb for the Beseler 23c is only 75 Watts. I think it might be slightly 'overrun', but not to the extent of a Photoflood.
    So, given that modern printing papers are faster than when that enlarger was designed, and that LED lamps are rich in the blue-violet part of the spectrum - making them more 'actinic' - a 60W equivalent (~ 7W) domestic LED bulb would probably work just as well as the original Tungsten lamp.

    Here in the UK, LED lamps with a plain opal end-cap and an ES fitting are pretty common, and so cheap that it would be no great loss to give one a try.

    Maybe a cool daylight (6500K) version would work even better in an enlarger, giving a similar light colour to a cold-cathode head.
  12. The optical system of the 23CII relies on a smooth white bulb surface about 1" in diameter. I think the later 2-step housing went to a slightly larger bulb with a larger base to improve the illumination and prevent imaging the area above the bulb on the neg. You'd need to duplicate that to get even illumination, but something could certainly be fabricated. LEDs have come a long ways in the last few years and would seem to be the ideal source for this application.
  13. Actually, I have been using a 23CIII for the first LED years until I reformed my home darkroom and discarded the Beseler. I used to have several bulbs in different strengths depending on the negative, so brightness was perfectly suited to each task. I try to remember the strongest one that fitted was 6.5watt (Philips). First higher watt bulbs were too wide to fit the housing in that era.
    I tested different bulbs, and I stopped using Photocrescentas, although I always had one at hand just in case. I think I never used them again in the 23CIII. LED bulbs were clearly superior.
    Original american flatter head bulbs were expensive and hard to find around here, so I only used a couple of them before switching to Photocrescentas, back in the nineties, I think.
  14. Rodeo, I always wondered about that "heat absorbing glass" quality... I have bought several of them for my different enlargers, always expensive original parts, Beseler and Durst amongst others.
    All of them look similar, greenish, actually a cheap looking chunk of glass for the mentioned Beseler. The Durst versions look pretty similar, although with a smarter polished cut. The Beseler has grinded borders, I didn't`t take a pic (the enlarger is packaged)
    Below is a pic of one Durst, near a big cheap glass plate used to flatten contact prints. I have a second Durst with a similar looking glass, 3mm thick. My oldest windows have the very same greenish tint, so I always thought it is either vintage technology (for sure, same as my windows) or something I cannot appreciate.

    Heat glass.jpg
  15. The image came out directly from the phone, the glass is actually clearer over a pure white sheet of paper.
  16. Schott make a KG glass series, which is genuinely heat (IR) absorbing, although ordinary plate or window glass will absorb some IR as well. The thicker the glass, the more heat it'll absorb.

    As you can see from that link, the Schott glass is darned expensive. When slide projectors were a thing, most of them included a 2" square or circle of cyan-coloured heat-absorbing glass; even the cheapest ones. So I suspect there's a bit of profiteering going on with the pricing of those glass filters.

    Dichroic heat-reflecting filters are cheaper to manufacture these days, and would be my first choice over a heat absorber. After a LED light source that doesn't produce much heat in the first place.
    jose_angel likes this.
  17. Some good ideas expressed here and some may work for you. Here is an alternative suggestion that I know some will not like but did you ever consider a light dimmer or rheostat to minimize the light intensity. I have a Omega B22 with its normal 75 watt tungsten bulb which I hooked up to a floor light me it works like a charm as I reduced the intensity about 33%. Never had any heat problem with negs either. I make sure that the the switch never moves so my results are constant. For contrast filters I never really noticed much change although in theory the color balance changed a little...I never had any issues with too little contrast. I use Ilford filters under the lens. Extends bulb life too.

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