Dear Dr. Ackerman,

I have read with interest your message below and hope I can offer some
explanation and assistance for your current dilemma.

Firstly, we are limited, both in terms of reproducibility and fineness of
stepping resolution by the way the Zeiss fine focus mechanism is designed.
Although elegant, the design is limited, I'm not sure how best to describe
it. In simple terms it's a sort of frictional clutch type mechanism
operating between the fine focus shaft and final drive mechanism.  However,
as this design relies on friction/pressure between the fine focus shaft and
a ball mechanism to deliver the final drive, slippage is inherent and hence
no guaranteed repeatability.

Because of the Zeiss mechanism design limitation, and feedback from
microscopists like you, we have developed a Z drive which attaches to the
coarse focus knob only, (the coarse knob, positively drives the nose piece
or stage depending on inverted or upright configuration  - therefore no
slippage).

We have designed our own 18:1 reduction mechanism which gives the Z drive a
stepping resolution of 50nm (0.05um).

Repeatability of the Z drive output is:
for moves </= 5.0um = 0.05um
for moves >5.0um = 1%

Incidentally, a 50nm (0.05um) resolution Z drive is also available on all other
currently supported microscopes.

Please contact your local Bio-Rad sale office, who can give you ordering/pricing
details of this new Z drive.  I hope the above information proves to be of help.

Best regards,

Dino Sharma
Confocal Product Manager
Bio-Rad Microscopy Division
UK

______________________________ Reply Separator _________________________________
Subject: Old BioRad 600 stage motor
Author:  Confocal Microscopy List <[log in to unmask]> at
Internet
Date:    25/09/98 11:37


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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