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[Neuroscience] Re: Automatic focus control for microscope?

r norman via neur-sci%40net.bio.net (by r_s_norman from _comcast.net)
Tue May 8 15:28:19 EST 2007

On 8 May 2007 09:38:19 -0700, tomte <tehgabriel from web.de> wrote:

>I am just curious about this: Does anybody know a solution how to keep
>a microscope in automatically in focus?
>It seems that some companys build this piezo driven objective holders
>which can be controled with a software that continuously takes a
>picture and compares it with a previous one. As soon as there appears
>some blur, the focus gets corrected via the piezo drive.
>I was wondering whether there is any alternative to this image
>processing procedure. For instance, measuring the distance between
>objective and stage via a capacitive device or a laser interferometer.
>Any ideas or comments?

I think you may be mistaken about what is needed.  There is no reason
for a microscope to go out of focus unless there is some really weird
temperature change that is causing expansion and contraction.  High
quality microscopes are very stable and don't change position so once
you put an item into focus it stays in focus.  Or you might have some
sort of weird flexible specimen that changes position as it absorbs
heat from the microscope illumination.  Standard preparations on glass
slides don't do that.

The real question has to do with what you choose to focus on.  With
high powered objectives, the field of focus is thinner than the
specimen you are looking at and so you have to scan the focus up and
down to see the full depth of the object.

Do you have particular trouble focusing or keeping focus?  Describe
your problem and perhaps we can help you solve it.

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