[pure-silver] Re: Light source vignette or hopefully avoiding it


----- Original Message ----- From: "Nick Zentena" <zentena@xxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, July 14, 2006 12:40 PM
Subject: [pure-silver] Re: Light source vignette or hopefully avoiding it


On Friday 14 July 2006 11:02, Frank Filippone wrote: 
Yes, but.....

You will have a possible issue where the 5x7 lower negative stage is
located. The aperture from a 5x7 MAY vignette here.


Is there any way to figure this out? Short of buying the light source and
trying I mean. Beseler manages to convert a 4x5 to 8x10 and the opening is
bigger on my Elwood then on my Beseler.

Could I draw the cone of light the image forms? Using the formulas for focus
to define the triangles? That makes sense doesn't it? It's then a simple math
problem. At least if I looking at the problem correctly.

Nick


The Beseler adaptor is a whole assembly with additional bellows and a different substage for the negative holder. I think you may have an easier time making an enlarger from an 8x10 view camera. The camera must have front focusing capability. The light source can be made using fluorescent tubes or compact fluorescent lamps. The ideal lamphouse would be a radio chassis box with the lamps mounted inside it. A new back must be made for the camera but that is fairly simple. Diffusion is gotten by using the plastic diffusion material used on light boxes, most plastics supply stores will have suitable materials.
The back is simple, you can actually make it from cardboard but light wood is better.
The light box is mounted on a support which also takes the camera. The camera should not have to support the light box. The new back is snugged up to the light box. The whole thing is mounted on a stand. For temporary use a heavy duty tripod will do.

To find the extension needed for the negative holder for the Elwood first determine the smallest print you will want to make. This determines the greatest distance from lens to film. Then find the focus distance for this size print. The angle of the cone from the lens to the film should be measured from approximately the center of the lens barrel (that is not exact but will do for this purpose). You can then solve the problem graphically. The adaptor must move the film far enough from the 5x7 aperture so that it will not mask the image.
There are formulas in several books for determining lens to film distance and angle of view.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx


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