Re: [Cameramakers] Enlargers and the related math

[DONALD MILLER]

Most typical diffusion light sources have a mixing chamber of some type. The apparent purpose is to create an apparent larger light source then what a piece of diffusion material alone would do. The mixing chamber is usually a reflective source that will "bounce" the light rays around before they actually are directed to the diffusion panel. In fact, most light bulbs are not shining directly onto the diffusion panel but in fact are directed to an interior wall of this mixing chamber.

The math for the degree of enlargement in the example that you are proposing is a 3X enlargement. I think that any enlarger design that does not include provison for focusing is going to be quite limiting and difficult to work with. That would seem to indicate the need for a bellows or some device of altering the negative to lens distance.

My 4X5 Saunders has a 250 watt lamp which is powered at 82 volts. The reduction in voltage is handled through the power supply. One of the reasons for the reduced voltage is that the power supply is regulated so that input voltage fluctuations are not affecting light output. I haven't gotten into the design of this source but would imagine that it has a "buck and boost" type design.

Considering the cost of surplus graphics arts cameras, why would you want to engage into the design of something that may or may not work. Alignment is critical for sharp print results.

I designed and had a machinist build a masking modification for my enlarger, the tolerances were held to less then .003 because anything with less tolerance would have been quite apparent as the degree of enlargement increased.

These are my thoughts on the matter. While I don't want to discourage you from doing what you envision, I think that the factors involved in successful design need to be addressed.

 Nick Zentena <[EMAIL PROTECTED]> wrote:

I've been thinking of how to enlarge 5x7 and 8x10 without buying an 8x10
enlarger.

It would seem a plywood box with a light source at one end and lens at the
other would be all that's needed. I spent some time with googles usenet
archives and saw people mention everything from 1100watt monster light
sources to 150watt work lights. Anybody know if a halogen work light would
actually work? The price is right. They generate alot of heat but I'm
guessing almost anything bright enough does. Some sort of diffuser between
the light and the negative holder would seem the easy way. Avoiding
condensors. A couple of fans to handle the heat? One pulling in room air the
other venting out hot air. Could I leave the top open? It would seem with the
lamp pointing down the plywood box not much light is getting out the back. It
would make cooling easier.

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Pardon the ascii art. Thats the basic shape. A negative holder in the middle.
A filter holder above it. Mounted on a table. With the easel mounted on a
wall. You'd move the enlarger forward/back to change print size. Or I guess I
could attach the easel to the table some how and make the easel moveable.

Now the math part. Lets say I'd like to make a 24x30 from an 8x10. Is that a
3x magnifaciton or is it 1/3?

The formula I have for figuring out bellows extension is

bellows_extension = (1 + magnifaction) * focal_length

But that's for the camera. An enlarger goes the other way. I'd like to use my
240mm process lens. It covers 5x7 at infinity but I'm hoping it'll cover
8x10 in this application. If not it's either the 210mm or the 360mm which both cover 8x10.

Thanks
Nick


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