Can I dither using an Astrotrac?

[starman1969]

I'm interested in possibly using the autoguiding feature on my Astrotrac in furure & wondered if this was possible.

[AstroAdam]

In theory, its the auto guiding software that'll be doing the dithering (or something interfacing with that).  So, if you use something like APT to take the shots, and PHD to do the guiding, then APT can talk to PHD and tell it to dither after each shot.  This should work just as well with an Astrotrac with an ST4 port as it would for any other mount with an ST4 port...

Somebody correct me if I'm wrong...

[StuartJPP]

I don't guide my AstroTrac but I have played around with it...

You will need to synchronise the taking of the image with the dithering of the mount. APT can connect to PHD(2) to do that. You need to set up PHD and run it first so that APT can connect to it. To get PHD to control your AstroTrac you will need something that can control the guide port of the AstroTrac. A guide camera like the QHY5L-II has got an ST4 port that can connect directly to the AstroTrac's auto-guide port (you need a special cable as the auto-guide port on the AstroTrac doesn't conform to the usual ST4 pin-outs). There are other options available like a HitechAstro USB to ST4 guider but might as well get a camera with an ST4 port on it if you haven't already got a camera.

Unless your polar alignment is 100% spot on you may still get some drift anyway (AstroTrac can only guide in RA). I usually get sub-pixel drift at the focal lengths I use on the AstroTrac. Compared to the first sub of a 2 hour session the last sub has a number of pixels drift that is enough to average out the noise.

I can't remember all the details as it was a while ago, but it is possible. You need to tell PHD to guide in RA only so that it won't try to calibrate or control it.

[starman1969]

Thanks for the replies, maybe I'm trying to jump before I can walk. I realise the Astrotrac can only guide in RA but I'd like to see it's limits. I could do with a guide camera now which doesn't need to be connected to a laptop.

[frostynixon]

Hello, 

BackyardNikon is a newly released capture software which also does the dithering. It also integrates with PhD guiding and all of your cameras are supported. For the D7000 you might need an extra trigger cable. You can download a 30 day trial of BackyardNikon. 

br

[starman1969]

Nice one. I'll get backyard Nikon.

[chrisvdberge]

Thanks for the replies, maybe I'm trying to jump before I can walk. I realise the Astrotrac can only guide in RA but I'd like to see it's limits. I could do with a guide camera now which doesn't need to be connected to a laptop.

I can recommend the Lacerta MGEN. You can connect it to the dslr as a timer and you can use dithering then as well.