Complete Teardown, Cleaning, and Reassembly of the Olympus BH-2 Coaxial Focus Mechanism Revision 4 Page 11 of 40
securing the brass focus rack onto the back of the
sliding focus block (see Figure 11).
Figure 11 – Remove bottom screw holding the focus rack
Carefully remove the (now loose) brass focus rack using
tweezers or needle-nose pliers (see Figure 12).
Figure 12 – Remove the brass focus rack
Check the Focus Block for Freedom of Motion
Smooth, free action of the sliding focus block is critical
to the performance of the focusing mechanism, since
the mechanical design of the coaxial focus mechanism
relies on gravity to eliminate the effects of the
mechanical backlash inherent in the rack-and-pinion
gearing mechanism. If the movement of the sliding
focus block is too stiff, this will cause a visible hysteresis
effect in the fine-focus knobs (i.e., there will be a
noticeable lag before the focus changes whenever the
direction of the fine-focus knobs are reversed, leaving
the operator feeling as if they are continually chasing
the focus).
With the focus gearbox and the brass focus rack
removed from the scope, the sliding focus block should
now move freely. Raise and lower the focus block by
hand and note the feel of this movement. The focus
block should slide freely without any noticeable
stiffness, sluggishness, or binding. Raise it to the top
and release it. It should drop quickly without any
significant lag. If the action of the sliding focus block is
found to be unacceptable, it will need to be
disassembled, cleaned of old grease, and reassembled
with fresh grease. The best time to do this is after the
coaxial focus mechanism has been completely
disassembled, since it is a bit easier to service the
sliding focus block while the other focus parts are not
present in the pillar arm. Although the procedure for
servicing the BH-2 sliding focus block is beyond the
scope of this document, it is fully covered in the
Complete Teardown, Cleaning, and Reassembly of the
Olympus BH-2 Sliding Focus Block document in this
series. You will be prompted at the appropriate point in
this document when you should perform the service on
the sliding focus block (if service is needed).
Remove the Fine-Focus Knob Caps
Before the screws securing the fine-focus knobs to the
fine-focus shaft can be accessed, the end caps on both
knobs must first be removed. These caps are held in
place with adhesive on their back surface. To remove
the knob caps, insert the tip of a tweezers or the tip of a
very small screwdriver into the notches in the caps and
gently pry the caps free from the knobs (see Figure 13).
Be careful when doing this, so as to not bend or damage
the knobs caps while prying them free. If the adhesive
does not release with moderate prying force on the
knob caps, use gentle heat from a heat gun to soften
the adhesive holding them in place, or squirt isopropyl
alcohol into the notches using a syringe or a small
dropper and allow the alcohol to soften the adhesive
for a bit before attempting to remove the knob caps.
Once you have removed the knob caps from the knobs,
be sure to place them someplace where dust and debris
will not foul the exposed adhesive on their back
surfaces.
Figure 13 – Remove the caps from the fine-focus knobs
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