2. Be especially careful when opening the access door to the lens (if
and opening it may cause the frame to sag allowing loose prisms to fall
out.
3. Bull's-eye panels may be set in the frame, or supported by adjacent rings.
If the frame does not support the adjacent rings, they are nested (see
Figure 3-2).
Bull's-eye
Nested Rings
Figure 3-2. Bull's-Eye Lens
4. Nested rings are very delicate. They should not be repaired on-site as it is
questionable as to whether they will stay aligned properly when
reassembled upright. Qualified personnel perform major repairs to these
types of lenses with the lens panel removed and placed on a clean, flat
surface.
5. Upon visual inspection of the interior side of bull's-eye panels, all rings
should be flush with adjacent rings. Run your finger gently along surface
to identify inconsistencies. Do not exert pressure. If any ring is out of
alignment or cocked, the lens must be repaired or catastrophic failure will
occur. Carefully, using your fingers, lightly tap on the outside of the
prisms. When tapping on a bull's-eye, ensure that you do not tap on the
inside of the lens. Always tap from the outside. The bull's-eye sections
are installed with a tapered fit in adjoining lens elements and can become
dislodged by exerting force on the inside of the lens. Listen for a solid
sound in response to your tapping. This tells you that the prisms are
solidly seated. If a rattling sound is heard, the prism is loose and may
become dislodged from the frame or adjoining bull's-eye pieces. Record
3-2
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