We have an old BioRad MRC 600 confocal with a focus motor that is a box 22
cm X 25 cm X 13 cm. The motor drive is connected to an upright Zeiss
Axiophot microscope. It works fine except when I try to do a 4D series, ie.
10+ z-series consisting of 20 sections with 1.08 um steps. After each
z-series the stage does not return to the same zero position. It is offset
by 1-2um in the positive direction (sample closer to lens--against gravity)
regardless of the direction of the motor during collection or the backlash
settings. This becomes a problem because the specimen of interest shifts
out of the focus range of the data collected.

My question is: has anyone else noticed this sort of problem. Did you solve
it and how? What is a reasonable precision for such a stage drive, +-200nm?

Note: the BioRad engineers are working on this but do not have an answer
thus far and admittedly it is an obsolete system.
Larry D. Ackerman
Lily & Yuh Nung Jan Laboratories
Howard Hughes Medical Institute
UCSF, Box 0725, Rm U226
533 Parnassus Ave.
San Francisco, CA 94143

(415) 476-8751  FAX (415) 476-5774
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