We only charge for overheads if these amount to more than 50% of the total exposure time of your image series. Anything above 50% will be charged at the same hourly telescope rate. Note that we never charge for overheads related to initial telescope set up (slewing, focusing, fine centering and guiding star acquisition).
We include charges for overheads in certain cases to to allow for requests with very short exposure times (down to 5 seconds) to be submitted. In such cases the overheads far exceed the total exposure time and we need to account for the effective telescope utilisation time.
What are overheads and how can I minimise them?
The observation request overhead is the extra time that is required during the fulfilment of an observing request to set-up the telescope for the observation (slewing to the target, focusing, fine centring and guiding star acquisition), and to process and download each single exposure (this includes filter change if needed, download time from CCD to computer, RBI flushing if present, and plate solution)
Overheads are automatically calculated during your observing request and are displayed in the Request Summary as you build your Image Series in the New Observing Request form.
The overheads strongly depend on how you structure your Image Series. The exposure time of your images will be the main factor determining such overheads. In short, if you use very short exposure times (e.g. 15 seconds), then overheads will be significant, and you will be likely charged extra. If the exposure time is long (e.g. 600 sec) then overheads will be minimal, and you will not be charged extra.
Binning will also allow you to reduce overheads, as the download times from the CCD to the computer will be much reduced. Note that binning is only available in some telescopes.