Do I have heat absorbing glass in my 23C?

Hi,

I have a 23c II and I have some focusing issues. It's probably popping. I'm trying to find out whether I have heat absorbing glass in my enlarger. The filter bay has a square piece of what looks like a plexi glass but I don't know if that's actually heat absorbing glass. Does anyone know if the only thing it could be is heat absorbing? Otherwise I'll try to find a HA to buy. Thanks

Normally, the heat absorbing glass is a thick greenish glass that is on top of the condensers.

Jon

ps on my 23cIIxl it is a round piece of glass held directly on top of the top condenser.

If it's Plexiglass, then it certainly isn't heat absorbing glass. If you need a piece of heat absorbing glass, it's not hard to find. B&H carries it as a special order product for about $50. You might be able to find a suitable piece of glass elsewhere for less, but you'd likely need to cut it down to size - not a difficult thing to do with a glass cutter, but a skill that does take some practice to master.

Well It might be real glass, I haven't looked at it in a while. But is that the place where it goes on the 23c? In the filter bay?

According to my ancient Beseler 23C Enlarger Manual,

"A Heat Absorbing Filter (Catalog #8042) is available to use in the Beseler 23C Enlarger. It is made of a special glass with heat absorbing properties. For printing color it is necessary to introduce a heat absorbing filter. The heat absorbing filter is placed above the condenser assembly and into the filter drawer (above the filters). First, raise lamphouse, then place the heat absorbing filter into condenser housing and above the upper condenser lens."

The Heat Absorbing Filter is listed as an optional accessory. That surprises me as I would of thought they all came with it.

An optional accessory? I don't think it's so optional if you're using a glassless negative carrier. While not likely, there is the possibility of overheating the negative to the point where it might warp. But I've got to ask, why are you relatively sure that your negatives are popping? I know there's a lot of talk about it happening, but honestly I've never seen it happen in an enlarger. I see it all the time with slide projectors, but they use far more powerful and hotter lamps than enlargers do. You would do well to consider other reasons as well. Check the alignment, make sure you have the right lens for the job, and most of all, make sure that the focusing mechanism isn't slipping. I've needed to adjust the tension on that for both my Omega enlargers. The 23C isn't that much different.

Negative Popping? How to be sure.

There is a simple way to see a negative popping with certainty (presuming that the head and focus are secure and cannot slip).

Adjust the focus until the grain is sharply resolved in the focuser within a short time after switching on the lamp.

Choose a small enough aperture setting that is comfortable to your eye for a fairly long viewing. Place your eye at the focuser and switch on the lamp. The grain should be sharp immediately. Continue viewing while keeping track of approximately how many seconds have elapsed.

The grain of a B&W negative will begin to lose definition and disappear into an amorphous gray if it bellies upward and out of the plane of focus due to heating. Using the grain focuser makes this quite obvious. This also allows us to determine just how long the negative will stay sharp before popping or to determine that it doesn’t happen.

If popping is a problem the exposure can be divided into a series of shorter exposures with 10-second cooling periods in between. Installing the HA glass will make big difference, but at the cost of 0.3 stops of light in the Beseler 23C according to my Minolta Flashmeter IV.

Popping seems to be a bigger problem for dense (likely overexposed or overdeveloped) negatives. I presume that the denser silver absorbs more heat than a normal negative making it more prone to popping.

I know there's a lot of talk about it happening, but honestly I've never seen it happen in an enlarger.

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I've definitely had it happen, with glassless carrier using 4x5 film, in a DII with a 200W bulb. It would pop out of focus every single time at about 10-15s. This caused me to really doubt the supposed sharpness of LF film until I figured out what was going on. It only happened on large prints, because exposure times were longer, apertures were larger, and depth of field was less.

Before I got my cold light head, I would turn on the enlarger for several minutes, and the negative would stabilize at the higher temperature. Then I could focus and enlarge. It was quite annoying though and I like my cold light head simply because I don't have any negative popping with a glassless carrier.

fschifano said:

An optional accessory? I don't think it's so optional if you're using a glassless negative carrier.

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Its right in the manual that comes with the enlarger. That is what it said. Of course, every single negative carrier is also an accessory. I guess its up to the retailer to sell you one or you already know, or you find out the hard way.

I just purchased a 23C from a fellow APUGer and I see the same clear plexiglass-looking thing. It is in the upper filter housing closer to the lamp (refered to as #3 in the manual). The only reference that I can find in the manual is that the enlarger comes with a filter holder. Is this what it could be? I thought a filter holder would be made of a different material, say metal or plastic.