Egg shaped stars when guiding ?

The base for all our tutorials, be it how to polar align or master astro imaging

Moderators: hawk_eye1975, budgetastro, martin_h


TUTORIALS SECTION

This section is only for the posting of actual tutorials, either single post or multiple, to ask questions or comment on a tutorial, please use the TUTORIAL DISCUSSIONS section where you will find a topic titled for each topic posted here, it just helps stop the topics becoming convoluted and lets the tutorials flow properly. If you post a tutorial, please also post a topic into TUTORIAL DISCUSSIONS with the same title.

Thanks.

Egg shaped stars when guiding ?

Postby Aardvark » Sat Jul 13, 2013 1:51 pm

This is a little checklist that I have thrown together that may help some avoid egg shaped stars. There are of course many possibilities, these are probably the most common when guiding.

1) Inaccurate guiding due to backlash in the gears driving the mount, this happens when the gear teeth are not fully meshed to each other. One way of avoiding this is to have the balance 'slightly' offset towards the weights in the RA balance, and usually biased towards the camera in the Declination axis.

2) Possibly field rotation, this could be caused if the chosen guide star were too far away from the intended target. For example if your target were low in the sky and your guide scope was using a star 10 degrees above this then the mount will guide to the guide star which has a different linear movement to the stars at the horizon. 1 degree movement from East to West along the horizon is a much greater apparent distance than a 1 degree movement of Polaris for example. The example given would be extreme but easier to understand. In practice the guide star should be as close as possible to the target.

3) Any cables snagging or trailing ?

4) (See 1) ), it is also a good idea to ensure that backlash in the gears is reduced, by moving onto the target and then manually slew scope to the East and slowly slew back to the West onto target. And similarly when on target slew scope slowly North and then South back onto target. I have assume balance is biased to weights and camera as above.

5) It could also be due to the settings in PHD not quite set correctly. There's a great guide HERE by Craig Stark author of PHD.

Hi, you are viewing as a guest, You can only see this first post in this topic. if you sign up you get access to other goodies you can't even see as a guest, including video tutorials on imaging and processing, scope modifications and even member discounts on gear!

So, give us a try, what have you got to lose! Oh, and if you stay, when you reach 50 posts you get access to MORE goodies! What are you waiting for!

User avatar
Aardvark
Global Moderator
 
Posts: 4999
Joined: Mon Feb 14, 2011 2:45 am

Return to TUTORIALS

Who is online

Users browsing this forum: No registered users and 1 guest

cron