Tips for DIY diffuse head for Durst 138s?

[blacksquare]

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

 

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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...

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[koraks]

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.

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.

- 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.

- 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.

- 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.