Negative Stage to Paper stage distance

[Andrew O'Neill]

Hi everyone, I have a big old copy camera I picked up at a high school that went digital. I want it for my 8x10 enlarger. My question is with a 300mm lens and a print size of 16x20 inches, what would be the distance from negative to paper stage? I am wondering if the column is long enough. Surely there must be a formula. Thanks!

[Lyle Aldridge]

We all know this, we're just trying to remember how to do superscript in html. The formula you probably want is:

D = F(m+1)²/m

Where D is the total distance from stage to stage, F is the focal length of the lens, and m is the linear magnification. Since you want to use a 300mm lens, and want a magnification of 2:

D = (300 (3x3))/2 = 1350mm (a bit over 53 inches)

This formula is technically for a "simple lens," but enlarging lenses are usually "simple enough" to make it accurate within a few percentage points. Bear in mind, also, that this all comes from a guy who studied optics as an astrophysics major only to end up as a lawyer. So it comes with all kinds of warranty disclaimers. I only remember this stuff (barely) from having more recently worked on physics homework with the four kids I'm now putting through college, and not a one of them is here to check my work.

[Andrew O'Neill]

Thanks Lyle!