In March I had the privilege to workshop with Alan Ross during which he spent time showing me the capabilities of the Ross Masking Technique. One of the things that became clear during our discussions was that this method would not work well with my D5 condenser lightsource. Not wanting to go back to the noisy and heat producing Chromega II head and having used a replacement LED source for the condenser head for some time, I began to search for a LED solution.
I am cold on cold light heads and, sadly, Modern Enlarger Lamps is not currently producing their Model 2. Finally, I was unable to convince my wife to sign the papers to take out a 2nd mortgage in order to afford the Heiland. As a result I went to Plan B which was to try to make one. Below are a couple of pictures of the Omega head so you can see what I needed to design to if I was going to build a replacement.
When I was in his darkroom, Alan showed me some details of his self-made LED head which we used a lot. The following design is adapted from many of the concepts and design ideas he so generously shared with me as to how it could be done.
My design parameters were: 1. It would be a ‘bolt-on’ replacement for my Omega Condenser head; 2. I would use filters (Ilford Multigrade, Rosco, [Arista] Color Printing Filters) for contrast control rather than a dial-in variable method; 3: It would use off the shelf LED components; 4) the negative holder for the Omega would still be used unchanged below the light source and 5. contrast filters would be above the negative.
I have attached pictures to this post to illustrate my design and a spreadsheet to show the LED configuration and source.
Top to bottom the components are:
1. a simple box of wood which serves only to act as the place where the lever arms of the enlarger (which are used to raise and lower the condenser head) connect. This was made with 1x6 lumber (over kill but I used to work for AT&T when it was the phone company and we designed phones to last 100yrs).
2. the above is connected to the lid (7”x10”) of the contrast filter holder box. This lid has the LED strip lights mounted on it. I used 1/4 inch Masonite type board to which I glued a 1/32 inch sheet of sheet aluminum. Then I mounted the strip LED light to that. I used the aluminum to give a better surface for the strips to adhere to and to dissipate the LED heat more evenly.
The LED strip lights and the driver (power supply) I bought from FlexFire. Alan had used another vendor but I found that FlexFire had an ‘ultra-bright’ option which put out more lumens per foot. Alan’s head had 12x12 inches of LED strips for up to 8x10 coverage while mine was only going to be 6x8 inches for 4x5. I felt I would need the additional light output. The configuration of my strips and wiring diagram is included in the attached spreadsheet. Also on that spreadsheet is the call out for the FlexFire parts I used.
3. The filter box is mostly just that - a box. The bottom has a 5 1/4 x 5 1/4 inch hole which sits on top of the negative holder. Inside it, it has 2 components: a) at the top I mounted 3 sheets of .05 Mylar in between 2 pieces of window glass to act as the diffuser for the LED light coming down from the lid; and b) in the front of the box is a hinged door through which I introduce the 6x6 inch contrast filters which sit over the bottom hole.
Total cost of components, including LED lights and driver, < $300 US.
Put it all together and paint it black and you get the head shown. I works well so far (about 2 weeks into its use).
In testing, I found that the brightness was within 1/4 stop of the brightness my condenser head (using a Modern Enlarger Lamp 1a light source) so I was happy there.
The only place I was surprised was when I was doing my contrast calibration testing using the Steve Anchell methodology laid out in his “The Variable Contrast Printing Manual”. I first tested my Ilford Multigrade filters and found that, while they were spot on for grades 00 through 2 1/2, grade 3 to 5 filters were producing <3. When I switched to combinations of Rosco filters, I was able to achieve grades 3 - 5, however.
While the spectral output curves of the FlexFire look like they are adequate, apparently there is something missing in the part of the curve that Ilford uses to balance out the exposure factor for those higher contrast grades.
For me this will not be a problem as I was planning to change away from the Multigrade filters anyway. Using combinations of Rosco Magenta and Yellow filters and/or Color Printing Filters, one can achieve finer differences in contrast than the 1/2 grade steps using MG filters.
Hope this was not too confusing with pictures and feel free to PM me or ask questions through this thread about anything that was not clear.
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