Linhof 72XL helicoid/calibration

Does anyone else have experience with the 72XL on a Linhof 617SIII. I

have two things going on with mine:

<br><p><ol>

<li> Focus seems a tad short at frame center. About 1/3" of rotation.

In particular, I can't focus it solidly at infinity. The difference

is fairly minor and easily resolved by stopping down. I'd venture to

guess that the infinity mark comes out to about 400-500'. Most of the

time though focus is short of infinity, so this is mainly a matter of

adjusting the position of the scale after determining the focal zone.

Occasionally I can't back up enough to guarantee the horizon, or

distant mountain, or moon, or some other feature is solidly rendered

at the expense of foreground. Stopping down seems a bit like an

ad-hoc workaround in this situation.</li><br>

<li>The field plane seems fairly curved; the edges focus noticably

closer than center. This wouldn't normally be a problem, except I

can't back the center beyond infinity to handle it as effectively as

I'd like. The only tool here is to close down the aperture, and in

particular to f/32 and beyond where the center now starts to degrade

visibly under a 22x loupe. I'd much rather focus beyond the infinity

mark at stop down to f/16-f/22 than focus short and stop down to

f/32-f/45 — for all kinds of good reasons.</li>

</ol>

It's still under USA warranty. Can I send it in for recalibration,

with a note that I'd like free play on the helicoid beyond infinity?

Can they do it? Either that, or adjust it so infinity focus is 1/2"

or so short of the mark on the scale.<br><p>

 

I've taken to shooting it using negative (B&W or color) in

high-contrast lighting without the center filter as the latter adds

noticable veiling flare that aggregates around image center as a large

lighter, slightly warm area. For low-contrast images I shoot

transparency film or substantially increase development for B&W, with

the CF in place. The CF is the monster Schneider one (95/112mm IIRC).

I use a flag (black) on a flexible arm attached to the tripod for

shade. The CF doesn't seem to add veiling flare in flat light, at

least nothing noticable to me.

Come to think of it, perhaps I'm overcompensating for the field curvature and that's what making it seem worse than it is. Hmm... I bet that's what's going on.

Jan, first of all I do not have experience with your camera but I have some suggestions. The 617 is intended mainly for scale focusing, in particular with the short lens like your SA 72mm. The scale on the mount should be about right at all distances up to infinity. If this is not the case you have the wrong focusing mount or barrel. It is very unlikely that Linhof supplies a lens which was not not tested before. I would contact Linhof at Munich/Germany directly by Email (ENGLISH is ok in Germany). This is a small company with customer awareness. They will tell you if the barrel or mount are in order or not.

 

The curved field seems normal, with that huge image plane a few millimeters of curvurture is within the spec of the lens.

 

By using the camera, it is not necessary to focus with help of a ground glass, unless at very near distances. The Schneider lens are designed to give best results at F22, although F8 and F11 can be used if you wish to handhold the outfit. The edges will become sharp only

at F16 or F22. F32 should not alter the performance much. I doubt that you can see the loss in performance with a ground glass. Instead you might see the structure of the ground glass.