Technical name of opal diffuser plastic material

[jose angel]

Well, I think I`m not qualified to talk about enlarging heads... I try to keep it simply and just working. Mine were made to fit the original head base, it is simply a plate with some LED lines (9 in total), that act as a top cover like a hat. The head base has a filter drawer that can keep a diffuser at the bottom. The previous one was an adapted OLED plate, which I much preferred, but that I modified a couple times to get the right illumination and coverage. I never found the perfect diodes to fit that mount. The enlarger is a Omega E6 type one I bought long time ago.
FWIW below is the fall off test print with a Componon-S 180 at working aperture, first with the 3mm sheet (left), then with the 4mm sheet (right) which loose almost two stops and with a more obvious spot:



And a fast straight print,



BTW, although heat is much lower that tungsten bulbs, they also get hot if abused and their working temperature is limited. The "hat" I made is intended to dissipate heat, but much hotter that the LED bulbs I have used in other enlargers.

The acrylic sheet I bought, at a distance of 2" doesn`t show the LED spots which are quite bright. Same as with the Durst diffuser I used for testing.

[Tin Can]

Very few 'qualified' experts survive. Now we try and learn.

There are few sacred cows.

[Drew Wiley]

There are more efficient methods of diffusion, with wider scatter and less light loss. But expect to pay a hundred bucks for a piece of material this size instead of fifty cents from the plastic shop scrap bin. I can provide info to anyone who really needs an alternative; but it's trickier material to fabricate. You can also double-diffuse with the ordinary acrylic sheet, with spacing in between, and of course, a bit of equivalent illumination loss.

[Tin Can]

Double layers of Makrolon LD works for me. https://www.curbellplastics.com/Rese...rolon-LD-Flyer

[brucetaylor]

I don't have any experience with the diffusion plastics, but I did make simple LED head for my Omega F. There is a thread here on the site somewhere about it. The LED panel I used was for transparency backlighting so it was fairly even to start with, but I had some unevenness. I used a sheet of diffusion (Roscoe I think) for movie/theatrical lighting. I spaced it off from the light source about an inch and used a picture frame with glass to support it. It works well and was very easy to make.

[Tin Can]

There are many ways to do anything. I use an enlarger without a lens for contact prints. I saw my diffusion was center hot. I took a piece of translucent plastic and made a center filter with a pencil.

Anybody here learn to do shading and gradients in drawing class?

I checked results with spotmeter and prints. No reason to improve it now...

[jose angel]

Drew and all, do you think the light loss I`m experiencing can be improved with a better diffusion material? I understand it`s a lens issue, so even with a perfectly flat light source there will be always the light fall off issue at the corners.

I think to have a perfectly even print, either the Randy`s center filter, or a "circular variable diode density/intensity" source design, or as you mentioned, an "aspherical" shaped diffusion element is needed. At a first sight, the complexity of the make and the easiness of a simple burning makes me think it could be not worth it. At the end, this level of fall off is what I have gotten with almost all the enlargers I have used.

[LabRat]

I have heard of someone making a center filter for a diffuser by using a very slow process film that was in contact under the diffuser and given a VERY brief exposure (possible with LED's or ND's over the lightsource or flashed), and developed to a low density, and mounted over the diffuser... The center of the film received slightly more light and built more density then the edges, so formed a mask... Worked well I'm told, but I never tried it (I went for using an oversized diffuser + mixing box, or put a mixing box over a condenser...)

Sometimes the problem is that the mixing box white has dulled or yellowed, and the edges reflect less light than the center area... Re-painting the mixing box interior with a flat white spray paint (give many VERY short/fast dusting coats over styrofoam to prevent melting) will bounce light inside more evenly... Sometimes reflective foil near inside edges of diffuser will help, but sometimes too much...

Steve K

[Drew Wiley]

Trying to inkjet print or airbrush what amounts to a center grad filter applied to a diffusion sheet has some inherent problems. First of all, is it going to be permanent or will it discolor and fade? Second (speaking in principle), are you contemplating color enlargement or merely typical black and white printing? It
would be hard to design something like this that is truly color neutral. Similarly with mixing boxes. An ideal paint for these is sold as "densitometer white", composed of 98% barium sulfate (significantly whiter and more stable than titanium dioxide), but around $200 per half pint. I found an art supply substitute that
that was 95% and a tenth that price. So far it hasn't yellowed in my 1500W halogen colorhead. Ideally, I recommend a polished aluminum or stainless steel "mirror box" instead of foam; but it's harder to design these correctly.

[jose angel]

Right, I tested a polished metal box with diode light and reflections made the thing useless... it was literally impossible to avoid them.
I wonder if a black housing in the LED option is a much better choice than white... Doesn`t an oversized diode plate will project the light beams without reflections over the diffuser? I made mine now this way.

LabRat`s idea seem quite good; maybe I can instead to scan and laser print a digital negative to be used over the diffusion sheet. I`ll work on it. Anyway, looking at the fall off test print above I find the resulting effect quite similar to any good condenser enlarger.

Out of curiosity, I want to check if "my" fall off is due to the lens or to the head (or a mix of both). I think it`s just matter of measuring the light at different points over the diffusion sheet (with a spot meter?). And I still have to compare it to my dichroic LPL.