RE: [Leica] how can the 75 Lux focus go bad?

["Dan Honemann" <ddh@home.com>]

> How exactly does one objectively check a new 75mm Summi to see if it has
> focus problems?  Thanks,  Steve

Tape some newsprint to a notebook or binder and tape a ruler on top of that.
Then open the notebook to an angle of at least 30 degrees (enough that you
will be able to focus on the 6" mark of the ruler, but not so much that it
is virtually parallel to the film plane, as you want the front and far ends
of the ruler to have some measureable distance from each other).

Using slide film, tripod and cable release, try this sequence of tests (best
to do this with multiple bodies and lenses, if you have access to them):

(1) position the camera's film plan at precisely 1 meter from the subject
(6" mark on the ruler) and the lens set to the "1" meter distance mark,
without focusing at all, then shoot;

(2) leave the camera/tripod at the same postion (1 meter) and focus the lens
so that the RF lines up perfectly on the 6" mark, note the precise location
on the lens barrel (hopefully it will still be on the 1 meter), and take a
shot;

(3) return the lens barrel to exactly the 1 meter mark and move the tripod
forward and backward until the rangefinder shows focus on the 6" ruler mark
(hopefully, it will be the same spot), measure and record the new distance,
and take a shot.

If all three measurements line up and all three shots are in focus,
everything is right and well.  If some of the shots are in focus while the
others aren't, then these tests should tell you whether the problem is a
result of just the lens being off or just the rangefinder (if it is both,
then all three shots will be out of focus).

Just one way,
Dan