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Changing from Reflection to Transmission Mode

Transmission mode is used for highest efficiency -- and lowest resolution. >From the specification,

``with the fibre slit in the nominal position, the wavelength coverage is from approximately 4450 - 7400 Åin a half field (edge to centre). Peak blaze intensity is at about 5860 Å''

An order sorting filter is generally used to prevent overlapping of orders --typically a GG495, which tranmits light from 4950 Åupwards, with 100% efficiency.

In transmission mode, the current mapping from slit and grating to the chip is:-

To change from reflection to transmission requires the use of the dedicated block and tackle found above the WYFFOS enclosure. At least two persons are required to carry out this procedure, one to handle the lifting, and the other to manipulate the camera.

Remove the top covers from the WYFFOS enclosure
Disconnect the camera cables (hartmann shutters, system cables, nitrogen flush and nitrogen supply)
disconnect the CCD cables from the side of the WYFFOS enclosure
free the camera kinematic mounts, and lift the camera about 100mm, and move it towards the door, away from the telescope end of the optical bench
rotate camera to face away from telescope end of the optical bench
move camera carefully to transmission position, taking care not to knock the valve on the pumping port
lower onto base
install grism into grating cell, with ruled surface away from telescope end of the optical bench
install collimator 2 into position - note it is out of balance, and will need clamping to its baseplate to stop it rocking
uncover relay mirror 2
reconnect camera leads, and CCD leads to enclosure
replace enclosure top covers