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Next Page: Protecting the IPCS - shutter discipline.
The operations described above are `automatic' exposures in the sense that the system can and will complete them using the information given in the queued command. There are (at least) two cases when this is not ideal.
When focusing the telescope, or focusing an imaging instrument, it is useful to collect in one data-set several images of a star taken at different focus-settings. If you have set up for two-dimensional data-sets and you give the command
ICL> rat_inter <channel>the system switches the channel to a special mode for focusing. Any of the run commands will now cause the system to prepare for an exposure but not to take data; the system enters a special pause state when ready to expose. Each time you give the expose command, the system superimposes one exposure on the data-set; if a CCD is in use, it is not cleared or read out; if the IPCS is in use, the buffer is not cleared between exposures. When you give one of the commands finish or continue, the channel unpauses and the date are saved as normal.
When using Taurus, it is normal to make three-dimensional data-sets, but not to expose the planes in their numeric order: the normal run command will not do. If the image format is three dimensional, rat_inter sends a channel into a mode where run, scratch, wink and glance pause after making ready to take data. You can then expose planes of the cube at will using the command
ICL> zplane <channel> <plane>After you have exposed all the planes you need, use finish or continue to unpause the channel and save the cube to disk. You may expose the planes in any order, and may leave some planes unexposed. You may also expose some planes more than once, if you don't approve of the results of the first try. If you do this with a CCD, the data from the second exposure replace those from the first. With the IPCS, the data from successive exposures to a plane are co-added.
Newtime can change the length of exposure between planes if you wish.
To get a channel out of interactive mode, use the command rat_auto. When the system is loaded or reinitialized, all channels come out of interactive mode.