Celestron AVX issues.

[HighHo]

I polar align normally as best as possible and mount using a (cheap) spirit level looks good. However I get some unexpected behaviour from where I have been doing long exposures where the image will shift up and then down, I would guess around 10mins without any adjustment the image is back at the same position  after doing a full cycle of moving up and down (i.e it has gone back to the orginal position twice, from moving down then up and finally returning to intial position)  and will continue in that way (it never contously moves off in a single direction). Often I cant get past 30second exposure due to this.

Does anyone have an idea what the cause of this behaviour is? Im planning on getting a guidecam soon which hopefully will elimate this, but would still be nice to undersatnd what I have probably done wrong!

[Thalestris24]

Hiya

It sounds like you are referring to periodic error which has about a 10min cycle? You can tune it out but it becomes a non problem if you guide. Drift aligning is also a good thing to do. This is easier if you are guiding and running PHD2 as it includes an easy to use drift alignment tool. One other thing, the AVX is difficult to balance because of stiction, especially in DEC. A way round this is to horizontally balance the scope off the mount using a dowel and marking the balance point then centering on the mount puck.

Hth

Louise

Edit: Your c8 has a long focal length so good PA and balance is more critical.

[HighHo]

Thanks I have considered the gears, but don't have anything currently to give me a PEC recording to playback. Once I get a guide cam I see what happens with PEC enabled (without the guidecamera active). I would agree balance can sometimes be hard to get perfect due to stiction (what a great word), the way the image moves up and down on the camera seems to perfect in my mind however for balance to be an issue. I have to admit I rarely do drift align but will give that a go and check the results.

Yet again many thanks for help.

[Thalestris24]

Hi

Yeah, you need an autoguider for pec training. I've never bothered with it. There's a useful video showing how to adjust gear backlash: https://www.youtube.com/watch?v=ORGleQBhkLw

Louise