REVISED 25th SEPT 2006
All calculations are now based on the actual telescope performance. The seeing criteria are:
The exposure time calculator is a Java 1.0 applet. It has been tested and found to run on the following browser/OS combinations:
If you have any problems, please contact the LT Support Astronomer with your browser and OS combination and any error messages you encounter.
To use the calculator, simply enter the apparent magnitude of your target, along with the desired signal-to-noise ratio. Then select the filter and binning. you require and press the "Do Calculation button". In general you should use 2x2 binning for RATCam. SupIRCam only supports 1x1 binning.
The minimum exposure time is set to one
second. We have not yet determined the minimum
reliable exposure time for the shutter to
allow 1% photometry, however it could be as
much as 10 seconds.
A risk of saturation is indicated by a minus sign preceeding the calculated exposure time. This can occur with bright objects (where there is little that can be done except possibly defocusing or not binning), or faint objects where the SNR requested is too high (where splitting the exposure into multiple readouts will provide a solution).
This calculator covers only RATCam and SupIRCam. For details of other instruments' sensitivity, see their respective instrument pages. (e.g., RINGO and Meaburn.)