Point Light Source...The Theory and Application

Billy Bob said:

Donald how do you get even illumination w/ your point source? I have 2 point sources and was considering using one to make a huge enlarger for 12x16 plates. I guess you are using the ps with the condensors in the 138s? I wonder about making a simple diffusion type enlarger with a point source sitting at the top of some reflector. Below the reflector I assume I would have to diffuse the light to get it even with ground glass or some other opal glass or white plexi. thoughts?

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I designed and built a reflector that evens the light across the condensers. I don't know of anyone who is using point light source in a pure diffusion enlarger. It would seem to be counter the desired effect.

From what I understand you to be saying, it would appear that what you are wanting is a diffusion light source and that could be done if you spread the light from the point light source and then diffused it in the manner that you indicate. I don't know what wattage your lamps are but plexi would be out of the question in my set up since I use 1000 watt lamps with an operating temperature of 500 celcius. That is over 900 degrees farenheit and would eliminate plexi as a viable diffusion material.

I think that if I were in your position and wanting to have a light source for 12X16 plates that I would opt for a source built from F15 T8 lamps. I would then diffuse the light with frosted glass beneath the lamps. There is a single sided frosted glass available that makes a very nice diffusion material and does not extract the loss of light that more heavily frosted materials do.

Good luck. Sounds like an interesting project.

Donald is certainly capable for speaking for himself most eloquently. Since I am also a user on a point light source I am going to offer an opinion here. The idea of using a point light source that is diffused seems to me to defeat the entiee idea. I believe that you would find very difficult getting even illumination. You will require some awfully big condensers to do this with a 12x16 inch negative..read as being hard to find and godawfully expensive.

There is another method of build a point light source for CONTACT printing. It involves the creation of a very long tunnel..say 20 feet. This may well require having corners with mirrors at the bends. This type of point light source is based upon the creation of long paralell light waves. Condit used to supply plans for doing this. This would more usually be used with a device known as a vacuum platen. The vacuum platen would hold the films flat wothout the use of glass. This can be used with clear glass instead of vacuum.. If the source that geneated this light was an colorhead then you could use it with ease to create color or VC printing.

Sorry to stick my paddle in this and supply answer to a question asked of Mr. Miller. No offense was intended.

What I am trying to do is just make an enlarger for the big negs. A diffusion enlarger would be pretty simple to construct, but I do have two nuarc point sources sitting here collecting dust. I'm not sure what the intensity is but they were made for printing contacts on stat type film as I understand it. Of course finding condensors big enough seems quite impossible so this is why I settled on the idea of a big diffusion enlarger. In reality its a silly project as I usually just do contacts of the big negs but it would be pretty cool to blow them up. If a point source would work with diffusion (to get the light evened out) then I'm sure I'de be satisfied with it. I don't know if I can get the light even over such a big sheet of film. I've not even tried the ps light yet but if its designed for contacts it should be relatively even at some distance from the film. Its just an idea i'm throwing around and before reading your post I never considered using the ps as an enlarger lamp source.

Billy Bob said:

What I am trying to do is just make an enlarger for the big negs. A diffusion enlarger would be pretty simple to construct, but I do have two nuarc point sources sitting here collecting dust. I'm not sure what the intensity is but they were made for printing contacts on stat type film as I understand it. Of course finding condensors big enough seems quite impossible so this is why I settled on the idea of a big diffusion enlarger. In reality its a silly project as I usually just do contacts of the big negs but it would be pretty cool to blow them up. If a point source would work with diffusion (to get the light evened out) then I'm sure I'de be satisfied with it. I don't know if I can get the light even over such a big sheet of film. I've not even tried the ps light yet but if its designed for contacts it should be relatively even at some distance from the film. Its just an idea i'm throwing around and before reading your post I never considered using the ps as an enlarger lamp source.

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If you are meaning the 26 1K Nuarcs then they are indeed used by a lot of alt process printers. I think that those are in the 1 to 1.5K range as far as lamp wattage. If the light is even across the surface then it would appear to be possible to use it for a light source. I was not aware that those are point light sources if that is what you have.

Point light sources have relatively short arc or filament length lamps with no diffusion and that is why they are called point light sources.

Good luck if you decide to try this. Keep us informed, if you will, of your progress.

Hi DONALD MILLER & CLAIRE SENFT,

I print B&W portrait (medium and large format negative) on Ilford Art300 paper. Your sharing is very informative and encourages me to explore Point Light Source further. I own the Durst L138 Point Light Source enlarger with coated T* condensers. But I have not used it to print any negative yet. It helped me now to "OCCUPY TILL I COME".

boon ching

Sorry to say that I have seen a post from either in many years. Still very good information.