Omega D2 LED Diffusion Head

[cardiomac]

Just finished this LED diffusion head for my Omega D2 enlarger. It entirely replaces the condenser head so you have to use under-the-lens filters. It works pretty well - the light is even and the multi-contrast filters work as expected. I used six Cree XP-E's at 1 ampere which generates about 900 lumens but the white acrylic soaks up about half that so only about 500 lumens hits the negative. The major thing that is not ideal is that the 24 volt power supply takes about 1.9 seconds to come on after plugging it in. The light doesn't ramp up; it just snaps on at full brightness after 1.9 seconds. I've dealt with it by simply adding 2 seconds to the time on the Gra-Lab but it would be nice if that were not necessary. Testing with a step wedge shows contrast is about the same as the condenser head which is surprising - I expected it to be softer. That may be a consequence of the spectrum of these LED's which are a little cooler than an incandescent bulb. The Cree LED's I'm using have a listed color temperature of 3000K. Overall I'm very happy with it and I can't wait to try it out on some real pictures.

[ic-racer]

Beautiful construction, thanks for sharing! Have you tried the timer interrupting the 24V circuit?

[Brian C. Miller]

Excellent! You might consider using a conventional transformer, zener diode, and pi filter for your 24V supply. Those come on instantly, and you won't have to compensate the times.

[Doremus Scudder]

Really pretty! When are you going into production?

As for the 1.9 sec. delay, one could just hold a card under the lens till the LEDs came on... If you use the Gralab in count-up mode, you may be able to just add a few "negative seconds," or just pull the card at the 5 second mark and just subtract. I print with a metronome and would just start counting when I pulled the card (I do this often anyway).

Best,

Doremus

[cardiomac]

Beautiful construction, thanks for sharing! Have you tried the timer interrupting the 24V circuit?

Thanks for the compliment. I thought about it but I wanted to keep it really simple and inexpensive. Right now it just uses an off-the-shelf power brick.

[cardiomac]

Excellent! You might consider using a conventional transformer, zener diode, and pi filter for your 24V supply. Those come on instantly, and you won't have to compensate the times.

That's a great idea. I had hoped to avoid making my own power supply because of cost and because I wanted something UL approved on the high voltage side. But you have gotten me thinking. Right now I'm using a desktop switching power supply (Phihong) but that's kind of overkill. I really just need an unregulated linear power supply that supplies anywhere from 20 to 30 volts DC. Current limiting to 1 ampere is done by an LM317 inside the lamp head to take advantage of the heat sink. At 1 ampere the 6 LED's drop about 3 volts each so the voltage will take care of itself. There may still be a short delay as the filtering capacitor in the power supply charges on start-up but as long as it is less than a second or so it will be acceptable. Thanks for the advice.

[cardiomac]

Really pretty! When are you going into production?

Thanks. I have a tiny bit more design to do before thinking about selling any of these. And I really want to solve this power-on delay issue. It doesn't really bother me but I'm sure it would annoy the heck out of many other people. But after all these issues are resolved, I was thinking of offering it for $279.00. What do you think?

[jeroldharter]

Thanks. I have a tiny bit more design to do before thinking about selling any of these. And I really want to solve this power-on delay issue. It doesn't really bother me but I'm sure it would annoy the heck out of many other people. But after all these issues are resolved, I was thinking of offering it for $279.00. What do you think?

I think you need an 8x10 version!

Somebody is selling an 8x10 conversion for Beseler 4x5 enlargers that looks like it is made of cardboard and household flourescent bulbs. The LED light source would be nice for that.

[Brian C. Miller]

The problem with an 8x10 version is the column height. Weight-wise, yeah baby! But how far that column can go up with, say, a 240mm lens on it is another problem. The best solution for an Omega 8x10 conversion is to put the new components above the lamp house stage arms, and then fit the lens to a cone. Then nothing gets in the way, and switching back is very easy.

[jp]

Beautiful work. I've never been able to get the crinkle-coat finish like that!

I'd buy one if it could be shown to have an even illumination comparable or better than traditional light sources and if it were for beseler. The vacuum/blower attached to my beseler dichroic head really spoils the tranquility of darkroom work.

As to the timing issue, the easiest thing would be to put a relay between the power supply and the head. Use something with a 120v coil, and you can power it with your existing timer. Something like 220919310097 would replace your timer and provide a relay. I'd put a switch in parallel with this item or your relay to allow override for focusing/composing.