Astrotrac AG

[winterlight]

Hi,

I just got the Astrotrac AG and put it to use for 2 nights now but have some trailing of stars. Polar alignment was done with polaris and the second 'alignment star' with the supplied polar scope to the best of my ability. Do not know how to do drift alignment. The setup was on a Manfrotto 055 tripod, 410 junior head. Exposure time 5 minutes with on a Canon 550D and 100mm macro lens. Is this likely to be polar alignment error or within the limits tracking error of the Astrotrac? Thanks

[davew]

Hi,

I doubt you've hit the limits with a 100mm lens. The most likely cause is alignment. This could be you or sag after you've set up.

Have a look at - Andy's Shot Glass - Drift Alignment for Amateur astrophotography,ccd, Neutonians and Refractors, amateur astronomy if you wish to have a go.

Dave.

[winterlight]

Thanks Dave. I read from the instruction that if both stars in the polarscope are aligned it should be reasonably accurate for about 100mm., Will check for any 'play' in the system.

[davew]

Hi again,

I must make it clear that I don't own an Astrotrac ! I have however seen many being set up and used. As an outsider I can see what goes wrong very easily.

The tripod needs a very firm base. The geared head must be tightened up very carefully so as not to throw the alignment off. Oh, and to state the obvious, the camera and ball head should be prealigned on your area of interest so as not to disturb anything if poss.

I know Richard Taylor winds his Astrotrac forward about 15 / 20 mins on the screw before his first exposure. So if he does it.....

I've also watched Gain Lee using a Tak FS128 and a lathe chuck as a counter balance. It often takes him quite a few drift photos until he's happy. Also he sets his tripod as low as he can manage to polar align. Normaly on his back.

And lastly. The polar scope may need a tweek. Can't help with that one.

Dave.

[winterlight]

Looks like there are quite a few things that I can improve on. Will try to improve things tonight, weather permitting. Googled polar scopes - quite surprised that these need alignment too! Thanks