Angulon 90 f 6.8 focusing mount

[Ricardo de Oliveira]

Hi,
I'm in the process of building a 4x5 PS around a Schneider Angulon 90 f6.8 and found in the auction site a m42 focusing mount that travels 7mm from open to close. How do I calculate if this is enough for focusing from portrait to infinite with my lens?
Sorry by my poor English.
Thank you in advance.
Ricardo

 

[paul_c5x4]

From http://photo.net/learn/optics/lensTutorial

1/So + 1/Si = 1/f

So - object to front principal point distance.
Si - rear principal point to image distance
f - focal length


If we transpose the formula and assume Si=f=90mm at infinity and then calculate for Si=97, f=90, we get So=1.25m. If my maths is correct, you should be able to focus from 1.25m to infinity with 7mm of travel (hopefully others will confirm).

If you want to check that 7mm movement is sufficient, build a temporary lens board and adjust it with spacers so that you can focus at infinity. Then add a 7mm thick spacer and see where it is focused on in front of the camera.


P.S. Nothing wrong with your English.

 

[Ricardo de Oliveira]

That´s it!
Thank you very very much.