v1.0 GDW 2004-May-03
During the April 2004 DEIMOS run, summit staff reported a problem
inserting a filter into the filter wheel. Investigation revealed
that the filter wheel had sustained damage and that several
filters were subsequently scratched.
We found that the filter wheel had been damaged at slot 6. The
"left" (dewar) side of the filter wheel (as viewed from the load
position) was found by summit staff to be bent inward toward the
filters, making it difficult to insert filters and apparently
causing the edge of the filter wheel to scrape across the glass
surface of the filters during changeouts. Staff immediately took
remedial action, bending the filter wheel away from the filters in
order to prevent further damage to the optics. Figure 1
shows the state of the filter wheel
following the intervention; the filter wheel is now bows out away
from the filter.
Three filters show significant scratches on the glass surface
(along the side facing the dewar) resulting from scraping against
a piece of metal which protruded into slot 6 on the wheel. The
worst scratches are on the NB8580 filter
new narrowband interference filter recently purchased by the
megamask teams) and the BAL12 filter
major concern, since GG400 can be used instead for most programs)
The V filter
is also scratched, slightly less
than the others. Observable effects resulting from this damage
have not been determined.
Photo showing the bent part of the DEIMOS science filter wheel as
seen from the filter load position to the side of DEIMOS. The
green arrows indicate the bent portion of the filter wheel; note
that this section is not parallel to the edge of the filter holder
as designed. This filter
shows the wheel as seen from the front of the
instrument; item 1 on this diagram shows the wheel (note the
relative thinness of the wheel at the centers of the filters).
Photo of the DEIMOS NB8580 filter, which apparently sustained
the worst damage. A series of scratches (note region between
arrows) runs the length of the filter, parallel to the direction
Photo of the DEIMOS BAL12 filter, with scratches the length of
the filter as indicated by the arrows.
Photo of the DEIMOS V-band filter, which apparently sustained
the least damage. The center of the filter is significantly
scratched and smaller scratches extend to the edge of the
filter (see arrows).
It seems certain that the filters were damaged during insertion
and/or removal from slot 6 on the DEIMOS filter wheel because part
of the aluminum filter wheel was deformed and protruded into the
path of the optic. We do not yet have any good ideas as to how
the filter wheel got warped in such a way as to scrape these
filters. It is highly unfortunate that 3 filters were damaged
before we learned of the problem. To avoid putting any more
filters at risk in this slot, we moved the R-band filter (which is
used for daily focusing and hence is never removed) into slot 6.
Gregory D. Wirth <firstname.lastname@example.org>
Last modified: Thu Oct 13 14:05:09 HST