It became apparent that the objectives, especially the low power (x1), were not correctly aligned. The MX-6T has a rotatable turret that holds two pairs of objectives. The x1 have individual focus adjustment, whilst the x3 are fixed focus. As you can see in the picture below, the objectives are normally protected by an outer shield, which is attached by three small cross-head screws. Once these are removed it is easy to access the outer locking screws for the objectives. Each has 3 grub screws that need a small Allen key nto turn them.
The procedure for setting up is to align the x3 objectives first, then the x1.
Whilst this description is for the Brunel MX-6T, several other stereo instruments are similar in construction.
Step 1
Using a ruler and a sharp pencil, draw a cross about 1 cm across
at the centre of the glass plate.
Step 2
With the optical unit carefully centred laterally on the pillar,
select the x3 objectives and set the focus when using one eye
only. Then look through the other eye only. Is the cross on the
centre of the field of view both times? If so then proceed to
step 4. You're in luck!
Step 3
Using the Allen key, loosen the outer two grub screws for each
objective that needs adjusting. Use one eye at a time, carefully
move the objective to centre the cross. When the first is set,
carefully tighten its screws without displacing the objective.
Then adjust the second so that the cross is central when seen
by one eye and tighten the screws. Using both eyes you should
now have a clear image of the cross.
Step 4
Rotate the turret to select the x1 objectives. As in step 3, adjust
one objective at a time to centre it. Also, adjust its focus so
that the image is sharp without need to change the main focus
from the position used in steps 2 and 3.
By now you should have all 4 objectives aligned and focussed on the centre of the stage. Check that when you change objectives the image of the cross remains sharp. Beware an effect that I experienced - if the adjustment of one objective is quite a way out and the cross is observed with both eyes it will be seen as a single cross - i.e the brain seems to reject one of the images rather than let you see two crosses not quite overlaid! Shut one eye at a time to check that all is well. If not, shut both eyes for a while and go back to Step 3 or 4 as necessary!
Step 5
Replace the shield with its 3 fixing screws.
Note: if the objectives cannot be moved sufficiently with only two grub screws loosened it will be necessary to remove one of the objective pairs, one at a time to allow access to the third screws. This is easily done if the 3 cross-head screws that hold each pair to the rotatable turret are undone but take care not to lose the locating pegs that help ensure the objectives fit in the same place when re-fitted. Also, don't swap the objectives over or the labelling on the shield will be wrong.
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