Re: Alignment of microscope optics - how...?

On 10 Feb, 19:58, Kevin Cunningham <sms...@xxxxxxxxxxxxxx> wrote:
On Feb 10, 12:56 pm, justbeats <steve_be...@xxxxxxxxxxx> wrote:





How does one ensure every component in the light path of a research
microscope is exactly central with respect to the optical axis? What
do you use as the reference to line everything else up against?

The question is prompted by recent efforts to correct a minor niggle
on my Zeiss ICM 405 inverted. The realignment required me to adjust
grubscrews in a the dove-tail mount to shift a component relative to
the centre line. I got stuck in an endless loop where fixing the
niggle introduced other alignment problems (usually vignetting) and
fixing that introduced yet more problems elsewhere. Argh!

I've got it all back where I started, the scope performs great, and
I've decided the niggle is bearable after all - until I know more. I
hope I'm asking the right question. Can anyone point me at more info
on this subject? Thanks in advance...

Cheers
Beats

PS. In case it helps, the specific niggle is with an optovar fitted
under the trinocular head. It delivers a full, unobstructed field of
view at all magnifications but the phase-telescope view is shifted
left of centre. Adjusting the grub screws on the dovetail recentred
the phase telescope image, but then the main (specimen) view is
vignetted with a black crescent around one side. Adjusting the
dovetail on the trinocular head to fix that problem brings the
original niggle back, and leaves the internal photo reticle off centre
(can't see an adjustment for that - although it is on a removeable
slider in the main body of the instrument). Given that EVERYTHING is
on a dovetail - where do you start...?

Beats,  what you need you probably can't get.  There are several ways
to approach this, what Zeiss did was to use a pre-centered eyepiece
and a dummy objective with a pre-centered target built in.  This was
strictly for repair tech and production techs so not a lot of these
were made.  However if you had one it was trivial to adjust everything
and then lock it in place.  With out one, well, its a lot more
trouble.

Now the interesting point.  This wouldn't have done a thing for the
problem you describe.  This problem is in the rotary part of the
optovar, actually in the phase centering section.  You have to adjust
that, put it back together and check, shampoo, repeat.  Don't under
any circumstances change the adjustment screws for the head, you'll
have the problems you described.

Thanks,

Kevin Cunningham
SMS- Hide quoted text -

- Show quoted text -

Thanks Kevin - I was hoping you'd pitch in ;-)

I initially wondered if the Optovar phase telescope alignment was the
only problem, and decided I couldn't do anything about it, even if it
was....

But then I noticed another "artefact" that led me to the centreline
question. Namely - if I center the illumination field diaphragm with a
certain slide in place, subsequently using a thicker or thinner slide
will shift the image of the field diaphragm left or right by a small
amount. I can't think of any mechanism that would cause this unless
things were skew-whiff with respect to the optical centreline. Maybe
this is the basis of a technique to get things properly aligned?

I'll take a longer look at optovar phase centering; but I've found the
"image shift" issue is still there with optovar removed so it seems
something else is out of whack (unless this image shift is normal; in
which case there's something else I don't understand. Doh!)

It's too late to "not adjust" the grub screws, I did it already and
have probably buggered the setup in the process - although general
optical performance seems brilliant to me.

I have two objective turrets (transmitted and epi) and they are
parcentric and parfocal at all positions, so I assume they're aligned.
Is that a correct assumption? Can I use the objective back focal
planes as references? If so - how?

What about these tools I "probably can't get". Are they *that* hard to
acquire or borrow? You say "without these its a lot more trouble"
which implies it's still possible. I've yet to follow the reference
from lumi, maybe the answer will be there, but can you point me at
anything else that describes alternative approaches to this sort of
alignment...?

Thanks for taking the time to respond. Appreciated.

Cheers
Beats
.

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