Guiding problem

[dark star]

Hi, the good news is that I finally succeeded in taking some guided images. So I am very happy! The bad news is that most of the images are not very good! I got a few good ones.

Guiding using PHD, APT, DMK41 CCD as a guide camera, finder guider. HEQ5 mount and Orion Optics UK 250mm f4.8 reflector. I attach two images taken at 90 second exposure, 800 ISO, taken one after the other. Canon 20D DSLR.

One is fine, the other isn't. Unfortunately most of the images are like the worst one! 60 second images seem mostly OK, but lots of problems with 120 and 180 second exposures.

Does anyone with more experience have any ideas? Bad polar alignment? But then why is one image OK and the other not? I took a dark frame with PHD at one point, but not between these two images.

https://dl.dropbox.com/u/82184859/IMG_4976.JPG

https://dl.dropbox.com/u/82184859/IMG_4977.JPG

David

[allcart]

One is slightly better than the other David, but both exhibit erratic movement. I would suspect backlash problems or a balance problem with your setup. I noticed this erratic behaviour on 1 in 4 subs I took a few nights ago. I was using a new rig and had forgotten to balance it correctly to keep the gears in contact. I altered the balance on my next test and it was fine again. It could be something as simple as that.

i am not familiar with PHD guiding so others may shed more light.

[dark star]

Thanks for the reply. Having thought about it, with my limited knowledge it could be anything from balance, bad polar alignment to flexture with the finer guider and guide cam I need to get out under the stars and experiment some more!

David

[Mav359]

I use to have real bad issues with PHD and its wild behaviour, the graph lookled like me walking around after a night out LOL

i went back to start, stripped the rig and re-balanced & things got a little better but then someone educated me on really properly polar aligning my mount and straight away i could expose for 5mins unguided and now i have gone beyond 20mins with little effort (no point mind cause of LP), it might not be your problem but it was all about polar alignment for me.

I think it safe to say the less PHD has to do the better it gets and the longer you can expose for, certainly this was the case for me.

[Spikey]

I'd make sure your polar alignment is nailed. Then balance will be crucial; what does that scope weigh? Are you pushing the mount a bit hard?

[Daniel-K]

was it windy? your pushing that set up to the max you have there there only meant to carry 18KG

[Tim]

The best guiding in the world wont correct for wind issues, and that's my guess here.

Next time, take a screenshot of your guiding graph from PHD and post that up, easier to see what sort of corrections are happening then.

Cheers

Tim

[Sam]

A 250 on a HEQ5 is certainly pushing the limits which may be a cause of the guiding problems.