Tips for DIY diffuse head for Durst 138s?

blacksquare · Sunday at 5:00 PM

Hello,

after a long and unsuccessful search for a functional CLS 301 color head on Ebay in Europe, I would like to build a diffuse light source for my Durst 138S. Unfortunately, HEILAND-type solutions are completely out of my budget.
I now have a condenser head with LED, it works, but I prefer the results from a diffuse light source (color head) on a second smaller enlarger.

I believe that someone here has already made something similar for their enlarger. I would really appreciate some push in the right direction, since I'm not an expert in designing electronic devices and I don't want to reinvent the wheel.

What do I need/don't need:
- purely diffuse light source that will sufficiently cover a 5x7 negative
- since I use the DA f-stop timer to my satisfaction and I want to continue using it, I don't need any controller. So I'm content with just a white light source and MG filters under the lens. But if it were possible to use green and blue LEDs, preset the "contrast", and then start exposure via a timer, just like with a color head, it would of course be great.

Current questions:
- I think that a light source other than LED doesn't make sense these days? Or should I consider a halogen bulb?
- Is a mixing chamber needed? Or can the LED array be placed directly above the negative, of course through a diffuser?
- what type of LED should I use? A few more powerful ones? Or a larger number of weaker ones, in the form of a strip? Heiland has 1600 LEDs in its source, which surprised me a lot.

Thank you very much for any advice.
Jan

cowanw · Sunday at 5:52 PM

For Sale - 8x10 " conversion durst 138s / G139

18x24 ( 8x10") conversion durst 138S / G139 all parts needed for the set up are included ! 1 x light head with 53 pcs 3 w leds with 2 x led 240V drivers atatched 110 volt drivers on request - same price 1 x pyramidal stub (?) on stainless mounting plate 1 x negative holder for up to 8x10...

www.photrio.com

koraks · 2025-11-03T03:02:49-0500

blacksquare said:
So I'm content with just a white light source and MG filters under the lens.

In that case you could either:
1: Put a white bulb where the bulb normally sits in the head, and place a piece of diffusion material in place of either (or both) of the condensers. This will not be very efficient, but since you can easily use a relatively high-power LED bulb, you should be able to get it to work OK. This will be the simplest option.
2: Replace the bottom condenser with a DIY contraption with white LED strips and a diffuser below them. A normal DC power supply as usually used for LED strips can be hooked up to your timer.

blacksquare said:
But if it were possible to use green and blue LEDs, preset the "contrast", and then start exposure via a timer, just like with a color head, it would of course be great.

You could do it like this: https://www.trippingthroughthedark.com/variable-contrast-led-head-for-durst-138s-progress/ which will be analogous to option #2 above. You would have to use two separate power supplies for the blue and green LEDs with a dimming option. Mount both dimming pots to a console so you can set blue and green power independently. Then hook up both power supplies to your existing timer.
Analogous to option #1 you could also mount a blue and a green LED source in the place where the bulb normally resides in the 138, bounce the light via the mirror onto a diffusor that sits where the condensers are now.

blacksquare said:
- I think that a light source other than LED doesn't make sense these days? Or should I consider a halogen bulb?

I don't see the advantage of a halogen bulb for what you're trying to do. I'd stick with LED.

blacksquare said:
- Is a mixing chamber needed? Or can the LED array be placed directly above the negative, of course through a diffuser?

A single LED source suspended above the negative that illuminates a simple diffusor probably won't give good evenness. You can solve this relatively easily (but at the cost of efficiency) by increasing the distance between the bulb and the duffisor. IDK if you're familiar with the Ilford 500 heads; those mount like a chimney on top of the 138 head where the mirror normally sits. You could do something like that as well. I've done that in the past and it worked OK, but it adds height to the enlarger.

blacksquare said:
- what type of LED should I use? A few more powerful ones? Or a larger number of weaker ones, in the form of a strip?

Either can work. Essentially, the bigger the light source, the easier it'll be to diffuse it, and vice versa.

There are many ways to skin this cat and the one thing they all have in common is that it'll require some testing to get even coverage. So decide on a concept, then do some tests and take it from there.

blacksquare · 2025-11-03T05:25:27-0500

cowanw said:
For Sale - 8x10 " conversion durst 138s / G139

18x24 ( 8x10") conversion durst 138S / G139 all parts needed for the set up are included ! 1 x light head with 53 pcs 3 w leds with 2 x led 240V drivers atatched 110 volt drivers on request - same price 1 x pyramidal stub (?) on stainless mounting plate 1 x negative holder for up to 8x10...

www.photrio.com

Thanks for the tip, I send a PM to Claudius, I'll see.

koraks said:
In that case you could either:
1: Put a white bulb where the bulb normally sits in the head, and place a piece of diffusion material in place of either (or both) of the condensers. This will not be very efficient, but since you can easily use a relatively high-power LED bulb, you should be able to get it to work OK. This will be the simplest option.
2: Replace the bottom condenser with a DIY contraption with white LED strips and a diffuser below them. A normal DC power supply as usually used for LED strips can be hooked up to your timer.

You could do it like this: https://www.trippingthroughthedark.com/variable-contrast-led-head-for-durst-138s-progress/ which will be analogous to option #2 above. You would have to use two separate power supplies for the blue and green LEDs with a dimming option. Mount both dimming pots to a console so you can set blue and green power independently. Then hook up both power supplies to your existing timer.
Analogous to option #1 you could also mount a blue and a green LED source in the place where the bulb normally resides in the 138, bounce the light via the mirror onto a diffusor that sits where the condensers are now.

I don't see the advantage of a halogen bulb for what you're trying to do. I'd stick with LED.

A single LED source suspended above the negative that illuminates a simple diffusor probably won't give good evenness. You can solve this relatively easily (but at the cost of efficiency) by increasing the distance between the bulb and the duffisor. IDK if you're familiar with the Ilford 500 heads; those mount like a chimney on top of the 138 head where the mirror normally sits. You could do something like that as well. I've done that in the past and it worked OK, but it adds height to the enlarger.

Either can work. Essentially, the bigger the light source, the easier it'll be to diffuse it, and vice versa.

There are many ways to skin this cat and the one thing they all have in common is that it'll require some testing to get even coverage. So decide on a concept, then do some tests and take it from there.

Thanks a lot!
It didn't occur to me to remove the condensers and put a diffuser in there. I thought the light definitely wouldn't be uniform with sufficient coverage. I'll try that.

Regarding the placement of the light source instead of the condenser...I read here or maybe elsewhere that the Durst Lacoli, which is located instead of the condenser, does not give completely uniform results for 5x7 negatives and a diffuse source larger than the negative is optimal. But the link suggests that it should work.

I know about Ilford 500, it's probably a similar solution to Agfa Color head + Durst Lavako adapter, which is now for sale on Ebay. I thought about it (agfa+lavako), but it's a really old model with hard to find lamp.

I have some LED floodlights at home (30W and 50W), so I'll try removing the condesors first and measuring the intensity and uniformity of light.

koraks · 2025-11-03T05:38:10-0500

blacksquare said:
.I read here or maybe elsewhere that the Durst Lacoli, which is located instead of the condenser, does not give completely uniform results for 5x7 negatives and a diffuse source larger than the negative is optimal.

I have one of those Lacoli sources - but I've never used it since it was broken when I got it. It was gifted to me by someone who knew I've built several light sources for my 138 and he thought I might be able to use the thing to good use. It's still on my (long and rather embarrassing) to-do list. So I can't verify that claim, but I'm not surprised. The Lacoli is/was basically a fluorescent tube inside a housing that fits in one of the condenser slots (it's supposed to go in the lower position I assume). Since the light source is pretty close to the diffusor itself (which is really just a piece of glass that's painted with a translucent white paint), I can see how hot and cold spots might occur.

If I were to build something based on the Lacoli concept, I think I'd exploit the fact that there are two condenser bays: use the top one for a light source, which would be an array of LEDs that's spaced in such a way that the light will be fairly evenly distributed to begin with. Then use the lower bay for a diffusing filter, so that there's a reasonably distance between the light source and the filter. This will help in getting even illumination.

blacksquare · 2025-11-03T08:39:22-0500

koraks said:
I have one of those Lacoli sources - but I've never used it since it was broken when I got it. It was gifted to me by someone who knew I've built several light sources for my 138 and he thought I might be able to use the thing to good use. It's still on my (long and rather embarrassing) to-do list. So I can't verify that claim, but I'm not surprised. The Lacoli is/was basically a fluorescent tube inside a housing that fits in one of the condenser slots (it's supposed to go in the lower position I assume). Since the light source is pretty close to the diffusor itself (which is really just a piece of glass that's painted with a translucent white paint), I can see how hot and cold spots might occur.

If I were to build something based on the Lacoli concept, I think I'd exploit the fact that there are two condenser bays: use the top one for a light source, which would be an array of LEDs that's spaced in such a way that the light will be fairly evenly distributed to begin with. Then use the lower bay for a diffusing filter, so that there's a reasonably distance between the light source and the filter. This will help in getting even illumination.

Yeah, Lacoli in the lower position, Lacotra (powe supply) above. I don't like fluorescent light sources, so I didn't even think about Lacoli, especially for the money they sometimes come up for.

MattKing · 2025-11-03T12:28:18-0500

FWIW, my relatively brief experience with the Ilford 500 head leads to a suggestion that you also add a red LED source to the blue and green sources - at least for the focusing part of the process. That blue and green light can appear quite dim!

koraks · 2025-11-03T12:30:04-0500

I agree @MattKing; focusing with white light is more comfortable. Instead of a red channel, you could simply add white LEDs too just for focusing.

MattKing · 2025-11-03T12:49:27-0500

the advantage of adding red is that it also aids with visibility when dodging and burning - I should have mentioned that initially.

DREW WILEY · 2025-11-03T13:04:36-0500

Those ancient slip-in Lacoli cold lights - if you can even find one that hasn't been stomped underfoot by a Brontosaurus - are way undersized and underpowered for serious work.

blacksquare · 2025-11-03T13:50:38-0500

Oh, I'm sorry, I don't understand how I could have forgotten that in addition to the DA f-stop timer I also use the DA enlarging meter, so I really only need a white light source. I've kind of gotten used to that system...

MattKing said:
the advantage of adding red is that it also aids with visibility when dodging and burning - I should have mentioned that initially.

That makes sense. I think Heiland lights up red for a few seconds before burn/dodge so that one can conveniently place the tools.

DREW WILEY said:
Those ancient slip-in Lacoli cold lights - if you can even find one that hasn't been stomped underfoot by a Brontosaurus - are way undersized and underpowered for serious work.

I have to admit that I like this prehistoric technique, but it's not much of a use anymore.

DREW WILEY · 2025-11-03T15:26:25-0500

Well, I have a cold light conversion atop one my of own 138 chassis, and like it a great deal; but that's a different story - a 12X12 inch Aristo V54 high-output blue-green model. It's timed with a Zone VI compensating timer, basically a light integrator probe plus a beeper.

The Brontosaur stomped sub-5x7 Lacoli is somewhere up on the loft in a big box of surplus components I never have used, including the entire original condenser head. I sold off all the condensers themselves long ago - looked like none of them had ever been used by anyone.

I don't think I'd want any system to light up by itself with red - what if you needed it for color printing too?
But Heiland would probably modify the controls if that were specified.

How the Durst did it for composition on black and white paper was with a swing away red filter holder under the lens. Now those come in handy for blue versus green split printing filters.

Tips for DIY diffuse head for Durst 138s?

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For Sale - 8x10 " conversion durst 138s / G139

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Tips for DIY diffuse head for Durst 138s?

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