Guiding - Take 1

[Dann]

Hi

Thought I would do a little write up of last night’s first play with guiding and PHD for your amusement.

I had the Orion Magnificent package through the post last week but haven’t had a chance to play on account of the weather (apart from some daytime focus adjustment)

I ran into a few silly and most probably avoidable problems you may be able to help with.

I setup as normal, polar aligned with the polar scope but had to play with balance for a while due to the little bit of extra weight. The only place I seemed to find a good dec balance was with the focuser and guide finder beneath the scope and in towards the mount. (Between the scope and weights if viewed in the park position)

This wasn’t a problem until it came to doing a 1 star alignment. The first alignment star is never in the field of view of my largest eyepiece so I use the finder to zero in, only I had replaced my regular finder with the larger Orion one. Due to the balance position the back of the finder lined up with the declination motor box on my EQ5 making it impossible to look through the finder. After a bit of faffing around I ended up just swapping the Orion finder for my regular one and rotating the OTA until I could see through the finder. Then I did my alignment put the Orion finder back on and rotated it back.

After that I just followed the PHD instructions in the guide camera booklet for connection and calibration. I didn’t change any options apart from the exposure length and set that to 3sec. No problems there, it seemed to calibrate ok and 10 mins later PHD told me it was guiding.

I intended to take a few test subs but with the full moon shining brightly even a 3 min exposure was almost completely white so I decided to run the guiding for half an hour.

The graph is below; I was hoping someone might be able to explain this to me as I’m not sure what it’s telling me exactly. The initial wobbles were caused by fiddling about with the imaging camera.

Thanks

[Merlin66]

The RA curve doesn't look too bad and I'd say the oscillations in the Dec are probably a balancing/ vibration issue...what does the graph look like a bit later? The oscillations seem to be reducing with time?

[Dann]

Thats as long a I ran it for unfortunatly, about 25 mins I think.

[Dann]

With the moon hiding away until later on I managed to take a few guided test subs last night.

I still had a similar graph to the above, as you mentioned I think it’s probably poor balance, so I’ll have to have a play around. I tend to think that as long as the subs look ok then it doesn’t really matter what the graph looks like. Last night however if one of those dips in the declination graph happened during an exposure then it was unusable as everything doubled up.

Other than that small problem though I’m very pleased how pain free it’s been to setup and get going out of the box. Now I’m looking forward to a long non work night to grab some real data.

Here are last night’s results, not really an imaging session but more an exercise in trial and error.

4 x 300sec @ ISO 800

Flats and bias used but no darks

Very quickly run through DSS and Photoshop

[bamus]

just now I am having same DEC graph as you did. My declination balance is is impossible to achieve due to short WO72 mounting feet. not sure how to overcome this

[shaunster]

bamus put a longer dovetail bar onto the WO foot and then you can mount using a proper dovetail.

[malc-c]

Dan, I wish my RA looked as smooth as yours...

One tip I picked up is balancing the OTA with it pointed straight up after you've done the normal horizontal routine. For me, I too have the eyepiece and finder pointing towards the weight bar in order to balance the ST80 and camera. Have a look on youtube for Astronomyshed's videos

[bamus]

bamus put a longer dovetail bar onto the WO foot and then you can mount using a proper dovetail.

have to think about that, but on the other hand I am imaging M31, which is close now to horizon, so I wouldn't thought DEC balance is so important. I suspect DEC motor problem or dec motor screw are screwed tight/light. Have to check it tomorrow.