Focus Problems

[Serge J-F. Levy]

I am a little stumped here and wanted to see if any of the veteran LF users who are VERY particular could help me out.

Though I THINK the camera doesn't matter, I am using a sinar x.

I am having focusing problems with my lenses. For example, with my rodenstock 150 5.6 apo lens, I'm not getting TOTAL sharpness across the field of the lens even stopped down to 16 at infinity. The lack of sharpness isn't at the edges as one would expect, but seems to be blotchy (minimally blotchy, but nonetheless noticeable) almost. The lens is CRYSTAL clear (i.e. no dust), has never been dropped or damaged.

What could be the problem here?

Many thanks,
Serge

www.sergelevy.com

[Jack Flesher]

I assume you are getting SOME areas perfectly in focus?

If so, one thing that comes to mind when you mention "blotchy" is moisture -- condensation -- on the film *OR* on or in the lens itself... This can happen when taking your lens, camera or film from a cold environment (outdoors, garage, refridgerator, air-conditioned car or building) and stepping into a warmer environment (outdoors, warm building) to shoot.

[Bob Salomon]

Rotate the lens on the board and see if the focus problem rotates with the lens or stays at the same place. If it rotates you have a lens problem. If it does not rotate you have a camera problem.

[David A. Goldfarb]

Blotchy focus sounds like a film flatness issue. Are you shooting with the camera pointed down, so that gravity could be a problem? What kind of filmholders are you using, or are you using rollfilm, and if so, which rollfilm holder?

Or are you seeing this directly on the groundglass?