ALFOSC 2nd-order blocking filters
Some of the grisms in ALFOSC give rise to substantial
2nd-order effects, especially for blue sources.
Information on the magnitude of these effects can be found
on the grisms page.
The following blocking filters are available for use with ALFOSC:
WG345, GG375, GG385, GG420, GG475, OG515, OG570
Please check this filter table, for
detailed information on these filters.
Most of these filters vignet
the field when mounted in FASU.
When mounted in ALFOSC however,
they can give rise to ghosting on the 0.5% level.
Note that grisms #5 and #8 have an in-built blocking filter OG515.
For grism #5
there is a remaining 2nd-order effect, see the Grism Table .