DSI III and field de-rotation
Posted 23 September 2009 - 03:56 PM
Instead of just tracking and stacking images by following the movements of one star, the Envisage Software with Drizzle will track and stack images locked on two stars, and can correct for image rotation that occurs if the telescope is tracking in the Altazimuth configuration, or in a roughly polar aligned telescope. Using this feature, you can do a quick alignment of your Meade telescope in Altaz, turn on the Envisage, select Drizzle, and draw a box around each of two stars in the field. The resulting image will not show rotational star trails.
I am wondering if anyone has used this feature? How successful is it? Can you really effectively eliminate field rotation in an 8” LX200 GPS in altazimuth mode with this feature? How long of a exposure is actually practical with this feature?
Posted 30 September 2009 - 12:26 PM
Posted 30 September 2009 - 07:27 PM
Posted 13 October 2009 - 08:58 AM
I haven't used Drizzle for a long time. What I understand Drizzle does is to de-rotate your subframes and stack them on top of each other, matching the stars you selected. However, as I understand it, what Drizzle doesn't do is to guide the telescope during each subframe. Therefore, you could end up de-rotating subframes that have star trails at the subframe level from movement during the exposure of the subframe. You final image would have a de-rotated field with stars with trails. Imaging in Alt-Az is possible if you keep the subframes short. Depending on the area of the sky in which you are imaging, you could conceivably get 45 second subframes in Alt-Az without significant star trailing. You could then use Drizzle to de-rotate these subframes from one frame to the next. Other programs do this as well, like Deep Sky Stacker. There is no way, however, that Drizzle is going to let you get 15 to 20 minute subframes. As pointed out, if you want to do that, a wedge is essential and you will probably need a balancing system. Rather than buying a second guide scope, rings, etc., you may want to try an Off Axis Guider and a guide camera. Everything goes through one telescope with two cameras - one imaging and one guiding.
Posted 13 October 2009 - 03:32 PM
Thank you so much for the insight. That seems to make sense now that you explain it. It is always good to have someone who can take away imagination and speculation and replace it with reality before something is bought and paid for. I appreciate it.
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