The OM is equipped with a filter wheel holding several optical elements
that can be moved into the light path. These elements, which are described
here, comprise not only lenticular filters, but also two grisms.
The complete set of optical elements is collected in Table 16.
Their arrangement on the OM filter wheel is indicated by the position
number on the filter wheel. Sequences of exposures using different
optical elements must always have increasing filter wheel position numbers.
Observations with the three UV broad-band filters UVW1, UVW2, and UVM2, for
example, must always be conducted in the order UVW1, UVM2, UVW2 (positions 7,
8 and 9).
From AO-16 (announced in 2016) it is possible for programmes with specific
approval by OTAC to perform several turns of the filter wheel. In other words
it is possible to perform series of exposures in which a sequence of
filters (ordered in increasing filter wheel position numbers) is repeated
|Filter wheel position number||Filter name|
|6||Grism 2 (visible)|
|10||Grism 1 (UV)|