See also the description of how to calculate the adjustments necessary to either
change the focal position (pure piston) or the vignetting character (tilt) of
the offset mirror.
There are three adjustment screws: two on the curved edge of the mirror next
to the slits and one on the opposite side. The first two are labeled "D"
and "E", and the third is called "C", although it is not
currently labeled. Your instructions should include a shift for each of these
- Rotate ESI until the panel between access panels "A" and "B"
is at the bottom of the rotator.
- Open the access panels "A" and "B" (3/16" Allen).
- Remove the small baffle that covers the lower part of the offset mirror,
beneath the two lamp projectors (2 red thumb screws; then lift up and towards
panel "A" to slide out).
- Use a micrometer to measure the height of all three defining points. It
is probably easiest to measure the distance from the top of the aluminum tabs
glued to the mirror to the anodized baseplate.
- Calculate the desired positions.
Note that adjustment screws "D" and "E" are 5-40 screws,
so that there is 0.025 inches per turn of each nut. Screw "C" has
a 20 threads per inch, so one turn is 0.050 inches.
- Adjustment points "D" and "E":
- Loosen the top nuts with a 5/16-inch wrench.
- Turn the lower nuts the calculated number of turns. You may want to
mark one face of the nut, or use an existing mark.
- Finger tighten the top nuts.
- Remeasure the heights measured in step 4 to confirm that the adjustment
- Once you are satisfied with the adjustment, slightly tighten the top
nuts on each post.
- Adjustment point "C":
- Remove the two nuts, washers, and springs holding the top plate onto
the defining point (15/16" if needed).
- Remove the top plate.
- Remove the left post that holds the top plate. This is to allow access
to the defining nut with a wrench.
- Note the position of the adjustment nut.
- Move the adjustment nut the calculated number of turns (13mm open-end wrench).
- Replace the post for the top plate.
- Replace the top plate, the washers, springs, and nuts. You only need
to finger-tighten the nuts at this stage.
- Remeasure the height to confirm that the new height is correct.
- Once you are sure the adjustment is correct, slightly tighten the nuts
holding the top plate.
- If desired, check the cleanliness of the offset mirror and inform Bill Mason
if the mirror needs cleaning.
- Replace the small baffle removed in step 3. Note that it is a tight fit!
- Close the access panels.