voltage control unit on a Beseler 23C

[bkrystad]

In the original manual for my grandfather's Beseler, it mentions a Beseler "Resistrol" Voltage Control Unit as an accessory. One of the uses it suggests is to control lamp intensity when you can't close down a lens enough to allow for long exposures (especially for dodging/burning).

I've posted before about my experiences with very short (10-14 second) exposure times with the 6-element 50mm lens I'm using (Rokkor-X). What I'm wondering is if anyone has had experience using a control unit such as this to allow opening up their lenses more on this bright enlarger.

Possible side effects? I've heard that changing voltage impacts the color spectrum of the lamp, and can possibly interfere with B&W results on multigrade paper. Is this true? Not sure I understand it completely, and not sure whether it's a show stopper. Any cautions?

If this accessory is generally a useful path to investigate for controlling my enlarger better, I'd like to explore it.

 

[john_s]

Lowering the voltage to an incandescent lamp will make it dimmer and lower the colour temperature (i.e. will make the light yellower). It will make enlarger exposures longer, of course. The contrast of VC paper will reduce as a result of the less-blue light. How much less? I don't have a clue, but if you really need to lengthen your exposure times, this will do it. You might notice some change in contrast, but I assume you'll be doing this only for small prints, and they can handle some small contrast reduction.

 

[Bryce]

I can't actually say whether this is a good way to go or not, not having tried it. There is at least one other possible problem with a regulator and that is consistency. If the voltage varies by much you are likely to end up having a hard time getting repeatable prints.
I've gotten by by sliding a 49mm ND filter in on top of the lens when I place the lensboard in there. Simple, inexpensive and functional.
I have thought about replacing my lamp with an LED one however...

 

[rxmd]

Why not just use an ND filter to gain a stop or two?

 

[bkrystad]

why not use an ND filter?

why not use an ND filter?

Excellent question! Because I'm very unsure what I'm doing, that's the honest answer.

My goal is just to bring the brightness of the lamp down a stop or two so I can use the middle apertures of my 50mm lens with my piss-poor negatives (read: thin). Of course, the better fix is to make better negatives, but that's a whole other path I'm stumbling down right now.

Got a hold of some ND+1 filter material this morning (I had never heard of the stuff). Now I get to figure out how to cut it and where to put it. The 23C has a 6x6cm filter drawer just above the lens, is that the place to put it? Or would you put it in the contrast filter holder between the lamphouse and condenser?

 

[ampguy]

You may want to consider a variac, or if you're handy, a box with a light bulb (sealed, of course) in series to drop the voltage without the noise from a dimmer unit.

For my projects with unregulated power supplies built for 115/120V max, I almost always need to use one of the above solutions or risk over voltage. Wall voltages are just higher now, than they were in previous decades.

 

[Beemermark]

My Beseler 45MX has the Resistrol and it's a very handy unit. I generally keep the bulb at less than full power, it really cuts the heat and popping down. Never had a any problems with B&W film. I only turn the light on full power for big prints and long exposures. If you can find one go for it.

 

[rxmd]

The 23C has a 6x6cm filter drawer just above the lens, is that the place to put it? Or would you put it in the contrast filter holder between the lamphouse and condenser?

I'd put it either in the filter drawer or underneath the lens with an external filter holder. I don't have a 23C, but if you put it between lamphouse and condenser it's likely to get too hot.

Philipp

 

[Bryce]

Unless the filter material is of excellent optical quality, I'd put it in the large upper drawer and risk cooking it. The reason, if you place it between the negative and the lens its imperfections will show up as lens aberrations. I use a filter that way with good results but that is just because it is a good camera lens filter.
The usual filter to place in the lower drawer is a red one so you can see the image on paper without exposing it, like when getting ready to burn.
So my contrast filters are the 6 inch size, cut down slightly to fit in the upper drawer.
Hope this helps!

 

[bkrystad]

success!

success!

After spending Thursday in the darkroom, I can report success with acetate ND+1 filter material in the Beseler 23C. I cut two squares to fit the acetate contrast filter holder that slips into the drawer beneath the lamp house. I also have a piece of heat absorbing glass above that, which should help protect the thin material from lamp heat. (However, at $6 for four square feet of filter, I'm not too concerned.)

I did two-second interval test strips with a cleared piece of film on f/22, f/16, f/11, and f/8, and found that the material was reducing the lamplight by nearly two stops, as I had hoped. Times to maximum black were 40sec, 20sec, 12sec, and 8sec, respectively. With this change and moving toward denser negatives, I'll have a lot more flexibility with my setup.

Thanks all for the help, as usual!