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Allineamento dello Zeiss Universal

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Aligning The Zeiss Photomic's "Headrig"
By Paul James
Anyone who has had experience of using one of the Zeiss Photomicroscopes versions
I, II, or III will have soon realised that the stand is a complex one. Such an
internally sophisicated optical device that was designed, manufactured then
assembled with a high degree of precision is no mean feat of optical and mechanical
engineering. However, the fact is that after 40 or 50 years of use and in various
ownerships, wear and tear PLUS the inevitable twiddling that some stands might have
incurred, would have undone Zeiss's original collimating sequences on the assembly
lines. Having acquired a Photomic II headrig a while back with the view of upgrading
my Photomic I's stand to support simultaneous observation/photographic facility I
soon found that both the headrig and original stand required some optical
adjustments to maximise their designed potential. I should imagine the fundamental
adjustments to the type II headrig are very similar on the I & III . It appears that
all 3 stands as well as the "Universal" share a very similar design scheme and so the
following sequencing and adjustments may therefore apply too.
I have not attempted to extend the alignment process into the internal 35mm film
cassette simply because I no longer use that facility: I suspect that few do these
days.
NB.......To simplify matters I have written this account from the perspective that
the microscope in question is obviously out of alignment, and that the owner will
decide to start from scratch. This avoids the writing of a more complex sequence of
procedures. I therefore advise anyone who feels comfortable with the prospect of
having to strip parts off and re-build to facilitate alignment in stages etc., to read
through the following notes entirely before starting. However, I cannot assume any
responsibility for mishaps or damage caused by accident or otherwise from your
efforts to collimate your own stand.
First things First
I repeat.... it is essential that the whole sequence I describe below is read through
before attempting any alignment work. Familiarising yourself with the sequences of
procedure is in my humble opinion half the battle, and reduces the chances of making
mistakes or false assumptions. There are 'traps' for the unwary along the way which
are easily fallen into, but as long as you make notes, and also use a felt tipped pen to
mark some exterior adjacent parts so that they go back exactly as originally found,
then little can go wrong. It is more than likely that you will be repeating some of the
procedures as you get nearer to true alignment, because one adjustment often
affects another, so it is necessary to whittle down the errors sequencially..................
It's rather like lining up a series of coins on your table into a straight line by viewing
from one end and tapping the each coin in sequence until eventually they appear in a
straight line.
My own method of adjusting the 'scope stemmed from the fact that some of the
optical parts or modules that make up the 'scope are not adjustable. Therefore logic
demands that we have to take this into account whilst planning any series of
adjustments.
The NON Adjustable modules are :a) The lamphouse and its iris. (Centering lamps only affect the eveness of illumination
within the source's field)
b) The Optovar (3) is fixed inside the objective turret housing module (4) , though
the housing as a whole is adjustable*.
The Adjustable modules are ;c) The prism slider assembly above the objective turret has the capacity for
tweaking in one plane only.
d) Both the trino/photo tube and binocular head units (1&2) have standard 120
degree grubscrew lateral settings.
e)* The Module (3) which supports both the Optovar unit and objective turret allows
lateral adjustment using 4 grubscrews around its perimeter.
f) The base unit's field lens/90 degree reflector module (6) can be adjusted.
g) The substage condenser is adjustable of course but having a subordinate though
vital role in microscopy, has no bearing on the collimating process.
Strategy
All the adjustments can be performed with the stand in its normal vertical position,
excepting the initial adjustments made to the base mirror/iris assembly (6). To
facilitate the adjustment of this component the stand should be tipped on its side so
that the base mirror assembly can be adjusted from the underside of the base whilst
allowing convenient access to both viewing ports. A paper back support under the
prism housing is ideal for this, reducing flexure to an absolute minimum since the bulk
of the top hamper is directly above it. Note that the bino head (2) can be rotated
into a more convenient attitude for alignment checks if need be. Once the initial
process of aligning the base's field lens/mirror assembly (6) is successfully
completed the 'scope can be worked on in the normal vertical stance.
Getting Started
Step 1) Without doubt the most important prerequisite before tweaking any part of
the headrig is to see to it that the light from the source is very accurately aligned
through it. Strictly speaking it is desirable to view the source from the farthest end
of the 'scope, without any intermediate optics in place which if present and a little
askew will prejudice the view of the source and cause misalignment from the start.
The prism slider module can be left undisturbed for the moment.
You'll need to remove the following : both substage condenser (5) and
Optovar/turret housing (3).
The Optovar/turret module is held in place by 4 grubscrews. One of which is shown
above. They may have locking screwcaps which are much shorter so these should be
removed first. With the 'scope positioned in the vertical, mark the interfacing of the
headrig and module with felt tipped pen to record their original mating position. Now
hold the module firmly before undoing JUST 2 ADJACENT grubscrews sufficiently
to allow the module to come away freely. By leaving the other 2 grubscrews
undisturbed will guarantee the module's intial registration when reassembled, which
should reduce time spent if it is required to adjust it later. Take great care when
lowering this Optovar/turret module because it is heavy enough to slip from the
fingers. You might like to slide off the turret dovetailed to it before removing the
upper Optovar unit to reduce chances of mishap.
First make sure the photoport is mechanically centered on the headrig, ie its base
appears uniform and concentric in relation to its counterpart on the headrig. Now
using a phase telescope in the photoport, with the prism slider set to simultaneous
viewing with binohead, scrutinise the field housing on the base unit (6) using an
external lamp to brighten up its surface. If it appears a little off axis true up the
photoport by adjusting it at its base on the headrig. Now adjust both the lamphouse
iris to minimum, and adjust the base iris (6) so it is slightly wider than the source.
Make sure your phase telescope is focussed on the upper iris leaves of the base unit.
The illumination can be adjusted accordingly. What now should be witnessed is the
state of the alignment between the source and the base iris's halo......quite likely
appearing askew :-
This image has been amplified for illustration purposes, your 'live' view through the
phase telescope will be smaller, but still easily interpreted.
Step2) The next task is to bring about concentricity of the source and base iris by
adjusting the field iris's mirror cell from underneath the base. The 'scope will have
to be tipped on its side as mentioned earlier. For simple convenience you can use the
phase telescope in the binohead swung around to near vertical to view your initial
efforts at aligning the light output. When effectively centered or nearly so, compare
with the photoport's view with the phase telescope. Unless you find both identical,
trust only the photoport's view for final tweaking.
The underside view of the base iris assembly is shown above. I think most Photomic
models are similar in principal. Note the 'horse shoe' clamp and its 3 screws. The 2
mirror cell clamping screws should be left alone. Getting the base's prism/mirror
assembly to accurately guide the source's light up through the dead centre of the
headrig is an operation that cannot be fudged and later annulled by adjusting the
headrig's components. It has to be as accurate as you can possibly make it.
Fortunately this is not too difficult to accomplish, though a trifle fiddly.
Before starting it should be understood that the mechanism for tweaking the horse
shoe support relies on a 3 point system. Each of the 3 screws, one of which is shown
above, is spring loaded, and importantly tightens against a threaded sleeve which has
slots visible around the screw head. By loosening each screw a little at first the
sleeves can be rotated either way to effect the lowering or raising of the horse shoe
support at that point. Use a fine watchmakers screw driver to rotate the sleeve. By
observation through the phase telescope you can see the effects of altering one or
more of these sleeves. The springs allow the effects of adjustments to by noticed
without need of tightening each every time etc.. When satisfied that the view looks
similar to that show below, you can 'nip' up each screw carefully....... the threads are
prone to strip in the aluminium alloy base. Be prepared to repeat the procedure as
alignment shifts a little when nipping up the screws. Patience is a virtue indeed but
finally, alignment should appear as shown below.
At last !
Step 2 We now have an accurately tweaked beam of light ascending through the
centre of the head rig's optical assembly. The 'scope can now be tipped back to
vertical. Next step is to replace the Optovar/turret module (3) back into its original
setting. Accomplish this accurately using the tell tale felt tipped pen marks with both
grubscrews back and nipped up. Now the accuracy of the original setting of the
Optovar/turret module can be checked. Set the Optovar on PH and observe through
an ordinary eyepiece back in the photoport through an empty objective port on the
turret, focussing accurately on the leaves of the base iris assembly (3). There you
will see a familiar view, albeit much enlarged, of the source's circle of light within (
hopefully) the base iris halo :-
This is a typical view after mounting the Optovar/turret module.....ie slightly askew.
This is of course a view directly through the photoport and the Optovar, the latter is
obviously slightly off line. The next step is to bring the Optovar's axis into alignment,
so the concentricity of the source/base iris appears true again. By doing this we are
also bringing the objective turret also into alignment as Zeiss have obviously aligned
accurately both Optovar and turret in the one module.
But before commencing, check again the binohead 's view with that of the photoport,
and if necessary loosening the main clamp screw at the base of the binohead and
adjusting the 2 grubscrews opposite. Defocussing the Optovar so as to expand the
source's circle of light facilitates the centering against the eyepiece field boundary.
The binohead's alignment can now be trusted when tweaking Optovar/turret
module.....and is of course far more convenient to use for this next operation.
Adjusting the Optovar/turret Module (3)
Now the fun and frustration really begins. You will soon find that getting the source's
light pool into the base's iris centre by adjusting these 4 grubscrews is not at all
intuitive. As a basic guide, each of the 4 grubscrews which point towards the central
optical axis, impart, when screwed in or out, a motion of the source which is exactly
at right angles to the axis of the grubscrew adjusted. Best to loosen slightly only 2
adjacent screws at a time and then nip up their counterparts opposite to see for
yourself the effects on the position of the source/iris combo. The trick whilst
supporting the slightly loosened module is to maintain firm interface contact with the
headrig as well as lining up the pen mark(s) with one hand, whilst nipping up/loosening
any of the grubscrews with other. Importantly don't forget that if you want to screw
in one grubscrew by one turn, then its opposite must be unscrewed one turn etc.. Try
to think in logical sequences as you work out how to move the source into the centre
of the base iris halo. Adjusting by small measures is the key to success, because
adjusting 4 grubscrews is much more complex to get right than 3.
The view you've been working to achieve!
When you have achieved this, the 'scope is very near to accurate
alignment/collimation, possibly subject to just a little more tweaking, but don't
expect a result in 5 minutes......it will in all probability take a lot longer.
Remaining Tasks
I have not mentioned the prism slider adjustment till now simply because in all
likelihood it will be fairly accurately aligned because the method of adjusting it is
hidden. But if you have difficulty marrying the 2 fields of the photoport and
binohead, it may be that the prism slider assembly needs a little tweaking too.
To adjust it.....unscrew the large cheese head screw completely . Loosen the 2 Philips
screwheads a 1/4 turn or so. You will notice the eccentric adjuster behind the large
central screw which when engaged with a screwdriver and turned offers some leeway
of prism assembly movement in one plane only. This can be checked through the
binohead and photoport. Its effect on the field in the binohead is much more
exaggerated than the photoport. I think therefore a small adjustment here which
might cure an alignment problem with your binohead, will have little or no material
effect on the photoport's alignment with the source. You can alter the photoport's
position slightly if necessary to bring into alignment with the views through the
binohead later. There is a fair amount of leeway inside the prism housing as the
prisms are much larger than they need to be. What matters most is that the
Optovar/objective/base iris/source alignment is still accurate, so a little
juxtapositioning of both the photoport/binohead to 'fuse' their imagery for
photographic convenience is entirely legitimate.
Finalising
At this stage your 'scope is pretty well aligned, but before putting away your
screwdrivers etc., replace with x10 objective or equivalent in its turret, and with the
substage condenser also back in place and centered, focus on a slide in BF then
remove it and examine the source's field boundary, more especially the edge of the
lamphouse source's iris. Open the substage condenser iris completely and then focus
the substage condenser on the edge of the source's iris carefully, and examine the
consistency of colour around its periphery, as you raise or lower the substage
condenser very slightly. What you should see is perfect symmetry of effects all
around the iris's edge. An even more critical test is to close the stand's base iris
down until it constricts the source's output. The dimming and any colour effects
should again be symmetrically disposed around the source's edge.
No matter how accurate your efforts have been, the fact is that the substage
condenser needs to be re aligned slightly with each objective on the turret. This
inherent lack of absolute parcentricity even from the best manufacturers
demonstrates that absolute alignment is simply impossible to achieve. All we can do is
get the source lined up through the headrig as accurately as we can.
Concluding Comments
It took me a while altogether to sort out and implement these procedures above. But
having said that I now have an 'accurately' collimated Zeiss Photomic stand which
performs extremely well especially in the more critically illuminated setups which is
precisely why I realigned it in the first instance. The final result was easily worth the
efforts and admittedly the frustrations that I'd put into the task. But be aware that
the process might have to be repeated in part as you progress through the stages. No
matter I believe, for the experience is truly beneficial in the long term, instilling
confidence in one's knowledge and ability to get the best out of your instrument. The
secret I believe in aligning/collimating optics is based upon the three
S's..............Symmetry, Symmetry, Symmetry !
All comments welcome by the author Paul James
Microscopy UK Front Page
Micscape Magazine
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Published in the April 2009 edition of Micscape.
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