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This procedure allows you to make a multiple exposure of a star image with the telescope focus being changed by an equal amount each time. The resulting multiple image is displayed on the Lexidata but has the status of a glance file - i.e. it is not kept unless the KEEP command is used (see Section 5.4).
The number of exposures required (1 < n < 10)
The exposure time in seconds
The direction in which the image moves on the chip (N,S,E,W)
Adam:> FOCUS 7 10 N
Perform a focus run with 7 exposures with focus increasing in the N direction each of 10 seconds duration. Alternatively type FOCUS and follow the prompts.
The current telescope focus will be used as the mid-point of of the focus run. Therefore if you wish to change this you should use SETFOCUS to set the telescope focus to the required value first. If the number of exposures is negative the focus will be decremented instead of incremented. The images are separated by a fixed amount of 20 arc seconds (40 arc seconds between 1st and 2nd) and focus is altered by fixed steps of 0.10 mm before each exposure. At the end of the procedure telescope focus and position are returned to their original values. To analyse the results see STARFIT (Section 4.5).
To change the focus increment (currently set at 0.1 mm default) use the FOCINC command
The focus increment step in mm
To change the amount (in arc seconds) by which the telescope is moved between focus exposures (currently set at 40 arcsec for the first two exposures and 20 arcsec thereafter) use the FOFFSET command
The telescope movement in arc seconds. (For the first two images it is twice this value).
Adam:> FOFFSET 10