A tale of minor triumphs and iamging woes.

[michaelmorris]

Well I’ve just packed up after yet another frustrating night trying to get to grips with deep sky imaging. However, there were a couple of triumphs.

Firstly, my Orion 80ED is now really easy to switch between my HEQ5 pro (for portable imaging) and the guidescope rings on the back of my LX200 - thanks Psychobilly for the great bolts!

Secondly, I’ve just tried out a light box I’ve built for taking flats on my 80ED. It works a treat.

Now the woes...

I gave my (new to me) HEQ5 another work out for an hour and I still can’t get Alignmaster software to work on it as it does (correctly) on my LX200. So I gave that up (again) in frustration and decided to have another bash at autoguiding. After about 30 minutes getting all the imaging stuff out and setting it up, I attached my off-axis guider (with Meade DSI-C as guidecam) and Canon 1000D to my 8” LX200. I got everything focussed and slewed straight to M27, not smack in the middle of the chip first time, but not far off.

I found a nice guide star, calibrated PHD and off I went. However, try as I might, I couldn’t get round stars more than once for any exposures of 30 seconds. Aaaaargh!

I have no idea what I’m doing wrong. After several abortive attempts, I decided to abandon the off-axis guiding and see if using my 80ED as a guide scope would be any better. No difference. I couldn’t get round stars for exposures of more than 15 seconds. PHD was tracking the guide star. However, some of the movements of the guide star seemed a little large before the mount appeared to react. I tried altering the exposure up and down with no effect.

At 2:20 am the clouds rolled in and put paid to my masochism. Perhaps next time I should start with autoguiding the Orion 30ED. Below is a 20 second exposre through my 8" LX200

Oh, the joys of deep sky astroimaging!

(NB. the exposure below is from a single 20 second frame. Despite being autoguided, the stars are still streaked.)

[Demonperformer]

Michael, I may be wrong, but isn't the LX200 an alt-az mount? If so, is the autoguider trying to compensate for the inevitable field rotation and in fact increasing the star-streaking because it can't?

I have no experience of autoguiding, so am probably talking rubbish ...

[TheThing]

I feel your pain sir! I have enough woes with webcam imaging. Keep trying and it'll all click into place.

And, undoubtedly, someone here with knowledge of this subject will be along shortly to give you some advice.

[blinky]

In my experience it will be down to one of two things

Either

a. Your polar alignment is some way off and the guider cannot compensate quickly enough

b. You have backlash problems - is the scope well balanced on the mount?

You also need to see if you can figure out which way the stars are trailing is it Dec or RA?

If you go to the (I think) tools menu on PHD you can enable the graph - see what it shows. Mine used to show it constantly over correcting so I had to reduce the aggressiveness in Ra.

Finally, keep with it! When guiding works it is the most wonderful thing to see nice 10 min subs coming through with no trails, you will get there, just keep being patient!

[michaelmorris]

Michael, I may be wrong, but isn't the LX200 an alt-az mount? If so, is the autoguider trying to compensate for the inevitable field rotation and in fact increasing the star-streaking because it can't?

It's on a wedge.

[anthony]

That just sounds like a typical night under the sky. I don't think you have done too badly to be honest.

If you are at 2000mm FL on the sct you have set yourself quite a hard starting point. Also looking at the image I wonder if the streak is more of a field flatness issue rather than a guiding problem.

I started with an Lx200 8" wedge mounted with an ed80 on top. I did not manage much with it but as coarse as a wedge can be, trying for a drift align can help refine the polar alignment. It is so hard to resist just imaging when you have a clear weekend night rather than fiddling with other issues.

Keep plugging away

[Ben Ritchie]

If you are at 2000mm FL on the sct you have set yourself quite a hard starting point. Also looking at the image I wonder if the streak is more of a field flatness issue rather than a guiding problem.

What's the PE on your LX like? Mine was something like 40"-50" peak-to-peak but very rough, with choppy bursts zig-zagging at 1-2"/second. That's very difficult to guide out, especially if you're using a 600mm focal length guidescope. You also need careful aggressiveness calibration, or the guider chasing the PE may make things worse, not better.

Also looking at the image I wonder if the streak is more of a field flatness issue rather than a guiding problem.

Mmm, think I agree - looks like the extended stars aren't all pointing in the same direction, as you'd expect for tracking error?

[martin_h]

Have you tryed EQAlign for polar alignment? Its free and I found it easy to use...might be worth giving it a bash.

[michaelmorris]

Thanks for the input guys.

I think you're right, perhaps I have been overly ambitous. I should really start by imaging with the 80ED until I get a bit better at it.

The polar alignment isn't perfect, but it's pretty good. At the moment I've been using Alignmaster, but I have a registered copy of WCS so I'll give it and EQalign a go.

The PEC is enabled, I'll try it with that turned off and see how I get on.

I have no field flattener in the imaging train. Next time, I try imaging with the LX200 I'll try it with an f6.3 focal reducer to see if that helps.

I'll keep on trying, but it's very frustrating when there are so few clear nights.

[anthony]

I can remember the PEC in the Lx200 being very diff to do. i was never confident that it was going to be implemented well. There could well be conflicts with guiding commands as well making a mess of things.

The 6.3 FF/FR will also help with the focal length and improve guided result. The Dumbell was pretty flat in my Lx200 for all of my MX7c chip which is tiny comared to your DSLR so those streaked stars are probably down to a lack of flat field.