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Before we start imaging there are three crucial steps:

  1. Precision point: make sure the scope is accurately pointing at the intended target
  2. Focus, focus, focus
  3. Set-up the auto-guider

Precision pointing is fairly easy to achieve (assuming the mount has been properly polar aligned). Simply slew to a known star using Cartes du Ciel, carefully adjust the scope until the star is dead-centre of your imaging camera field of view and then use Cartes du Ciel to "sync" the scope to the adjusted position. If, during the evening, you slew to a very different area of sky, you might want to redo this synching.

Focusing takes a bit more effort but it is so important to ensure crisp images. If I'm way out of focus (perhaps having changed focal ratio with a reducer, for example), I actually find it easier to use the manual focusing knob to get reasonably close. Typically I'll take short (1s) images of a mag 3 or 4 star until the star and fainter field stars look pretty sharp. Then I hand the reigns to AstroArt's autofocus facility (see screenshot below). Once you've taken a test image, you draw a focus box around the focus star and press the Focus button on the CCD Control window. This will show a magnified version of the focus star which is refreshed after every exposure.  If you not press the "PC" icon to open the Ascom Autofocus window where you select your focuser (mine is the FCUSB from Shoestring Astronomy) and connect. From here if you select the Autofocus tab you will be given a number of options which will control how the autofocus routine will operate:

  • Steps - how many steps away from the current 'zero' position it will move to try and find a better focus
  • Increment - how big each of those steps will be
  • Expo/Step - how many focus exposures will be taken at each step. If the seeing is poor you go for 9-10 to average out the wobble, otherwise 4-5 seems fine.

I usually re-run the autofocus routine just to be sure but generally get great results. It's important that you don't pick too bright a focus star - if it's saturated because the exposure's too long for that bright a star the focus algorithm can't work so well and you either need to reduce the exposure or pick a fainter star.

Of course all this auto-focusing relies on having a remote-controllable electric focuser. I use Meade's #1209 Zero Image-Shift focuser and remove its handset from the 3.5mm jack and insert the output from the FCUSB focuser controller which AstroArt controls through ASCOM

Auto-guiding is started when you slewed to your imaging target and have identified a suitable guide star. I've talked a bit about how to select the right guide star and the right guide exposure in the Autoguider section of my Software page. Once the auto-guider has calibrated itself and the green cross-hairs are in position you are ready to start imaging.

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