[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 1:00 PM
Subject: [pure-silver] Re: Light source vignette or hopefully avoiding it


On Friday 14 July 2006 15:40, Nick Zentena wrote:


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.


I did some back of the envelope work. It seems if the negative stage is more
then about 3" above the 5x7 opening I should be okay. Using a 240mm lens. I
wonder what a longer lens will do to things.

Nick

Since the light path to the film will be longer for a given size of print the angle of view will be narrower and the distance from lens to 5x7 aperture can be larger. I don't think this would be helpful. Because the magnification ratio is probably not going to be more than about 1:5 a 240mm lens should have sufficient coverage. A longer lens, as always, will have somewhat less fall off at the corners. 240mm is a fairly wide angle lens for 8x10.

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

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