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[jdman]

I have a 21cm Xenar mounted in a compound shutter in a 4x5 crown and notice I only have about 1 inch of bellows left on the track. In Laymans terms what determines the amount of bellows extension it takes for a given lens? The lens clears the lensboard by about 1/8 inch on all sides but will fit. This lens must add about 2 lbs to the camera. Russ

[Les]

The official definition of the focal length is the distance from the rear nodal point to the ground glass when focused at infinity.

the rear nodal point is where the rays of light entering the front of the lens converge to a point.

For most of our purposes that rear nodal point is close enough to the lens board to ignore it.

Unless this focal lenght was different than the rest, a Xenar is a Tessar formula and shouldn't be radically different in bellows draw than say a 203 ektar (which isn't a tessar, but is close in focal lenght)

I'm wondering if there isn't something fishy about the lens. I don't know if Schneider did the same, but Taylor, Hobson, Cooke made cells, for certain lenses that would extend their focal lenght.
The effect is the same as adding a Telek lens but these were full rear cells.

I just remembered that the pair of cells I have cluttering my desk is a 210 Xenar. Let me go find what I did with the shutter and get back to you.

[Les]

Okay I cobbled my Xenar back together and came up with a bellows draw of just SHORT of 8" which suprised me. I would have expected something slightly longer than 8"

here's the photograph of the bellows when focused at infinity



_________________
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[ This Message was edited by: Les on 2003-07-07 06:49 ]

[jdman]

Need to send you a picture, how do I do it? Looks like my lens has a spacer in it and you have about 3 more inches of track. Russ

[Les]

send it to

LNPHOTO@TWMI.RR.COM