Kurt, have you considered electrically tunable lenses for focus control rather than peizos or steppers?  I don't know much about them but I am sure others on the list could share their experiences. I would have thought these would be popular for issues like this (fast focus in thick specimems) if they preserved image quality. 
Q for the thread: Are they useable for high N.A. objectives?
Andrew Eisenhawer

Sent from my Samsung device over Bell's LTE network.

-------- Original message --------
From: Craig Brideau <[log in to unmask]> 
Date: 06-18-2015  3:53 PM  (GMT-07:00) 
To: [log in to unmask] 
Subject: Re: Z-imaging with base motor instead of piezo. 

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All my laser scanning systems use stepper motors for focus control, usually
moving the objective rather than the stage. For video-rate imaging they are
probably too slow, but if you are only doing a frame or two a second they
work perfectly well. I have a collection of Nikon Ti frames with motorized
focus, an old E800, and some Thorlabs stepper motors that all seem
sub-micron repeatable. I would only resort to piezo if I was trying to
acquire fast X-Z or Y-Z images. For the XYZ volumes typically collected in
my lab the regular stepper motors are more than adequate.

Craig

On Thu, Jun 18, 2015 at 9:24 AM, Kurt Thorn <[log in to unmask]> wrote:

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>
> The microscope stand motor will generally be much slower than the piezo
> insert, both because the long travel range makes it difficult to use a fast
> piezo motor and because the mass that's being moved is much larger.  But
> the precision of these stages can be quite good. The Nikon TiE can be
> driven in steps as small as 25 nm; I'm not sure how accurate it is at those
> step sizes, But I imagine it's pretty accuracte. Many years ago we acquired
> Z-stacks with a 200 nm spacing with a stepper motor attached to the fine
> focus knob of a microscope, and they seemed quite accurate, so accurate Z
> motions can be achieved with pretty simple technology.
>
> Kurt
>
>
> On 6/18/2015 1:22 AM, Anton Kamnev wrote:
>
>> *****
>> To join, leave or search the confocal microscopy listserv, go to:
>> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
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>> *****
>>
>> Dear colleagues,
>>
>> In our LM core we normally use piezo stage inserts (e.g. PRIOR) for
>> acquisition of Z-stacks. Those work fast and reliable but very have
>> limited
>> range (100~400 um). Moreover, stage inserts are often bulky and we
>> experience a lot of problems fitting large specimens/slides into them.
>>
>> Obvious solution would be to get rid of piezo inserts and use base motor
>> instead (which moves objective instead of sample). This would give more
>> manoeuvre space at the stage and much bigger travel range. Unfortunately
>> most of base motors are rather slow and often lack required precision.
>>
>> At the moment I’m looking into purchasing of new scope and thus wondering
>> if
>> there have been any advance in microscope base manufacturing.
>>
>> The question is - are there microscope bases which would move objective
>> with
>> speed and precision matching those of piezo inserts? If so, I would
>> greatly
>> appreciate if you could share your experience with those.
>>
>> Sincerely,
>> Anton.
>>
>> Anton Kamnev, PhD
>> Imaging Manager
>> Mechanochemical Cell Biology Building
>> Division of Biomedical Cell Biology
>> Warwick Medical School
>> The University of Warwick
>> Coventry, CV4 7AL UK
>> tel: +44 (0) 24-7615-1934
>> cell: +44 (0) 782-408-6941
>> email: [log in to unmask]
>>
>>
>>
>
> --
> Kurt Thorn
> Associate Professor
> Director, Nikon Imaging Center
> http://thornlab.ucsf.edu/
> http://nic.ucsf.edu/blog/
>