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Prime focus photography

The prime-focus (PF) camera is fixed to a pedestal within the PF cage, the pedestal and cage being mounted separately on the top-end ring. The rotatable cage is designed to accommodate one person. It is possible to change top ends in the night in less than an hour and demounting the CCD camera takes about 30 minutes, so divided nights using the CCD and photography (with the doublet only) are feasible. Interchanging any of the three correcting lenses, however, requires removal of the camera, with the top end off the telescope, and is not practical at night. The camera head carries an autoguider probe, shutter, filter holder, spot sensitometer and nitrogen flow inlet, all of which must be operated from within the cage.

Prime focus characteristics

Table 7.1: Characteristics of the prime focus correctors

The autoguider will work with stars as faint as 15th magnitude. The spot sensitometer pattern is projected through the telescope filter on to the plate only if both are the 10x10 inch size.

Photographic plates

The camera has holders to take 10x10x0.06 inch and 5x7x0.04 inch plates. The table below lists the range of emulsions available in 8x10 inch (5x7 size is being discontinued) and typical exposure times for these emulsions when used with the triplet corrector. The doublet is 15% faster. Emulsions are normally hypersensitized before use to improve their long-exposure quantum efficiency.

Hypersensitizing is normally carried out by AAO staff, but visitors are welcome to mutter incantations over their plates if they feel it helps.

Table 7.2: Photographic emulsions and exposure times

Other filters available in 10x10 inch size include GG 395, RG 530, RG 590, RG 715 and an Halpha interference filter (bandpass 100Å). There are also two composite glass filters designed to give classical B and V passbands with J and F emulsions. Sky limited exposures are ~ 20% longer than the normal J/385 and F/610 combinations.

Considerably more detail on photography is given in AAO UM 5 Photography with the AAT, a HTML version of which is now available.

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Next: Prime focus CCD Up: Direct imaging and Previous: Direct imaging and

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