3.5 Skyflats

Narrow band flats can be taken as early as half an hour before sunset. Broad band flats should be taken 5 – 10 minutes after sunset. Move the telescope to Zenith (Z button on the ACE tool bar) and make sure you're looking at a clear part of the sky. Some people like to track during flats others not, it's your decision. Take a few Test exposures in CIA to make sure NetDDE is enabled. When NetDDE is enabled, header information will be supplied to the black window in the CIA interface. Make sure CIA is talking to V by checking that CIA is monitoring the CCD temperature.

The filter wheel should initialize when you start up CIA, but if you are unsure it's also a good idea to initialize it again before you start changing filters.

Don't start flats until the CCD temperature has reached –90°. Set Image type to "Flat" and assign an Object Name. The default number of exposures is 5 (this can be changed). You should probably begin with a 3 second exposure to minimize shutter structure. The Flat window comes up when the exposure is done. Mean and Max counts are displayed at top of this window. The Max must be less than 25,000. The Mean can be anywhere between 10,000 and 20,000. If you would like to save the current Flat and need to change the exposure time for the next Flat, change exposure time BEFORE YOU SAVE THE CURRENT FLAT.

If you decide not to save the current Flat, click NO and it will continue the sequence until you have 5 saved Flats. If you want to cancel the sequence you should do so before you decide whether or not to save the current Flat.

Once you have the desired number of saved Flats in this filter, you can change filters and begin the process again. You have about 30-40 minutes of dusk time during which it is possible to take Skyflats. It can be pretty tough to get a set of 5 flats in each of the 4 broad band filters in one sitting, so you have to be sharp and ready to go as soon as the sky is dark enough to begin.

Remember: Top off the dewar after Flats to maximize the hold time. Topping off should be done with the telescope in the stow position. The stow position is equivalent to the Custom Park position and also to the Mirror Cover Park position in the telescope pull down menu.