Re: Stereozoom microscope repair
- From: "Chuck Olson" <chuckolson01@xxxxxxxxxxxxxxxxxxxxx>
- Date: Thu, 5 May 2005 15:35:26 -0700
"Jim Stewart" <jstewart@xxxxxxxxxxx> wrote in message
news:S7SdnbpZuvSLP-vfRVn-gA@xxxxxxxxxxxxx
> Kevin Cunningham wrote:
>
> >
> > Chuck, e-mail me off site and I'll help as much as I can. I'm a tech
so I
> > might be able to help. Could you please not pick on techs? A buddy and
I
> > have been planning to post old parts books on the web.
>
> I have a couple old stereo microscopes and I'd
> enjoy reading your dialog. Could you post it
> for everyone?
>
>
Hi, Jim, Aaron, Kevin, and Richard,
Thanks for your suggestions and offer of help.
I actually received considerable help by email from another tech who works
on these microscopes. He pointed out there are two adjustments that can take
out small "double image" problems and "zoom drift". One is the movable
objective lens on a flat plate held with two or three screws you see when
you look at the bottom end of the microscope pod. With this one adjustment,
I was able to improve the white microscope to the point where it's no longer
uncomfortable to use, but it still is different from a normal microscope,
and should have further work done. The black microscope's vertical offset is
much greater than what this small "objective shift" can compensate for but
for a final tweak after everything else is within specs, this pretty well
"mops up" all effects of mechanical and optical tolerance.
The second adjustment for "zoom drift", which I call "eyepiece shift" is for
correcting the condition where the center of the field of view shifts to the
side when the zoom knob is moved through its range. I find it's pretty tough
to define a center of view at low power that stays centered all the way to
high power, but if you check the center first at high power, it usually
winds up "fairly well" centered at low power. When "fairly well" turns out
to be "nowhere near", then maybe the "eyepiece shift" adjustment is in
order. This adjustment can also change image offset, but probably should not
be used for that due to its interaction with "zoom drift".
To implement the eyepiece shift, after unscrewing the eyepiece tube (the
painted part) from the microscope, you will see the dust-protective glass
cover held by a threaded ring which should only be finger snugged, and
should be easily removable (for cleaning if it need it). With the ring and
glass removed, now a second heavier ring with larger notches for wrenching
can be removed, allowing the ring with outside threads and three setscrews,
under the tabbed washer, to be shifted by adjusting the setscrews. To see
the range achievable with adjustment of the setscrews, they may be totally
removed and the ring threaded back into the eyepiece tube, held on the
microscope body tube and moved around by hand. In my case, in the black
microscope, even that extreme of that shift wasn't enough to correct the
vertical offset, and of course, there's no point in increasing the "zoom
drift" even a little if it doesn't fix the image offset, so that was left as
found.
So what's next? Since the image offset in the black microscope was beyond
the range of provided adjustments, it looked like I need to examine the
mirror system for a loose or shifted mirror to find the cause. Fortunately,
only the left mirror system had to be checked. All four mirrors are each
held by a retainer clip which presses the mirror against a trio of precision
pads on the pivoting casting. There's a small amount of airplane-glue like
cement applied to mirror edges to keep them in place through normal
handling, but rough shipment or accident can break a mirror loose, and if an
edge rides up onto the cement, the tilt will have an obvious effect. The
only way to examine the mirror system for a loose mirror is by taking out
the pivot and stop screws, removing the casting and releasing the clip to
allow the mirror that's out of position to come free. (It might take a
considerable study of the mirrors and their contact with their pads to
decide which one needs to be revised.) Then after cleaning up the cement
buildup from the casting and mirror, replacing the mirror and clip should
restore the precision of the optical path. After everything is put back
together and checked for correct operation, the mirror can be re-cemented
for permanence.
In my black microscope, the second mirror from the eyepiece end had a
retainer clip that was obviously out of position and I could see a sliver of
light between the mirror and one of the three pads it should have been in
good contact with. I removed the clip and mirror, scraped a bit of cement
from two of the pads, and replaced the mirror and clip. A quick reassembly
confirmed the double image situation is now in range of the "objective
shift" adjustment to superimpose them at the highest power setting. After a
final reassembly I made a little tool to move the objective lens on the flat
plate, consisting of a 1/2" long piece of 9/16" o.d. brass tubing soldered
to a 3/8" wide strip of copperclad PCB material as a handle. In use the
tubing is pressed up into the lens recess of the flat plate and moved around
until the images are perfectly in register. Then the microscope is removed
from the stand and inverted while the two screws holding the flat plate are
carefully torqued down. A final check at all zoom settings confirmed the
lens setting made with the tool had not been moved. My $15 microscope is now
a bit more valuable, and I learned quite a bit in the process.
Thanks for posting comments and to the tech who took me under his wing - -
many thanks indeed.
Chuck
.
- References:
- Stereozoom microscope repair
- From: Chuck Olson
- Re: Stereozoom microscope repair
- From: Kevin Cunningham
- Re: Stereozoom microscope repair
- From: Jim Stewart
- Stereozoom microscope repair
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