Need help working 1to1/4to1 on Deradorff 5x7 Special

[saverio]

Hi,

Thanks in advance for your help/advise.
Is there a simple formula for determining lens use, bellows extension, and image size?
I'm trying to do a series on lips close to 1to1 or greater magnification. I tested my 10 3/4 Artar at max extension on my Deardorff 5x7 Special (22inches?) and got close to 1to1 but find I want to be closer, maybe 4to1. Do I go longer or shorter in focal length to achieve my goal?

Saverio

[Jack Dahlgren]

Hi,

Thanks in advance for your help/advise.
Is there a simple formula for determining lens use, bellows extension, and image size?
I'm trying to do a series on lips close to 1to1 or greater magnification. I tested my 10 3/4 Artar at max extension on my Deardorff 5x7 Special (22inches?) and got close to 1to1 but find I want to be closer, maybe 4to1. Do I go longer or shorter in focal length to achieve my goal?

Saverio

Yes, the magnification is given by the formula:

M = f/(f-s)
M is magnification, f is focal length, s is distance to subject.

The distance between lens and film can be calculated using the thin lens formula:

(1/subject distance) + (1/distance from lens to film) = 1/focal length.

From these we can see that if you are already using maximum extension and want more magnification that you should use a shorter lens.

[Robbie Shymanski]

Unless you have the ability to extend your bellows, you might be best off finding a lens with a shorter focal length. On my 4x5, I use and old 135mm Zeiss Tessar for shooting 1:1 or greater. Gives me a lot of flexibility. I also found it helpful to recalulate the actual f-stops by measuring the iris diameter and focal lengths when focusing.