help to improve guiding

[Erquy]

Hi,

after 2 years of imaging unguided (with AVX mount, either with a C8 at F10, or F6,3 and recently with a WO GT81, 0.8FR and using canon EOS1100d as imaging camera), I decided to go for guiding. I have a Lacerta EOS oag with a Costar guider. I use Phd2 and through ST4, all basics works.

I could set up and made some trials with the WOGT81/0.8 and to my surprise I got 10 min subs with all round stars from the 1st trial and I could even find a small window to try with the C8 at F10 and also manage 10 min sub (but only 1 before clouds come in as it took some time to find a guiding star, so not real conclusion there, but it looks good ;-). In case of the GT81, the OAG/costar works great, no issues to find a guiding star, works great.

I did pay attention to balance as well PA (after being used to image unguided, I can say I am trained to make sure I have a good balance and good PA with the AVX -I typically manage 100% usable subs for 1 min sub at F10,  90 sec at F6,3 and 180 sec with the GT81, and I could push a bit further, but I prefer to insure 100% of usable subs, so I always set this exposure time).

So a very good guided start, but now I am looking at PHD lab to understand better and I see big differences on RMS.

based on 2 different session with the GT81:

1) a combined RMS of 1,63" for the guider on 1 hours run (targeting the Rosette nebula). Below link to 5*10 min

http://www.astrobin.com/170146/B/

2)  a combined RMS 0.92" for the guider targeting M51 (the moon was up and thin clouds came in, so I took only 2*10,  and they were very much washed out, not usable, but I still let it guiding as it could to simply see how it worked, and it run for 1 hour very well)

As I am imaging with the canon EOS1100d, above RMS are well satisifying and as mentioned I got great results in both cases on 10 min subs.

All setting basically the same as default input from phd2 (RA aggressiveness 70, hysteris 10, mm, min pix 0,21, max 2000ms). I did the calibration for each night, and taking into account the declination of the targets for the calibration steps. Calibration worked out without any problems reported.

During those 2 sessions , I did change up and down some of RA (in a range 50 to 90), hysteris (in a range 5 to 15) min pixel move (0.15 to 0.26), but I could not see effect on the combined RMS for each  runs (some little up and down, but 0.1). I used 2 sec exposure time for the guider.

RA Osc inbetween 0,30 and 0,35 which I understand is a good value.

No particular strange deviation as I have seen reported in some phd graphs.

My questions:

- is this expected that higher RMS will be obtained, if one imagine near the equator as compared to imagine near polaris with basic same setting (Iwould guess so as less to work out for the move near Polaris?) as I have seen comparing targeting M51 and the rosette

- is above results decent ones, or shall it be possible to get even better results.If so, what factor shall I look at to  further improve?

Thanks for your help and comments in advance!

below a screen shot of the 2 runs I refer above as from Phd lab.

[kalasinman]

I'm learning too, but yes results would be expected to be different near the CP as near the CE. As far as improving results, how are your stars? As far as settings go, you don't show any of your settings so hard to make a suggestion.

[ollypenrice]

I can't help with PHD settings but what I would say is, don't expect to be able to make fine tuning comparisons across different nights. The stability of the seeing has a large effect on the guiding values so I would only trust comparisons made within one night.

I think RA is more difficult close to the celestial equator, as you suggest.

A trick which sometimes reduces oscillation in Dec is to guide in one direction only - the direction needed to correct any polar misalignment. (Perfect PA is not usually possible.)

At those focal lengths you are doing well!

Olly

[Erquy]

Thanks for the comments and confirmation on the increased sensitivity towards the celestial .equator.

I will look at dec guiding in 1 direction next time out.... (and i don t know when... I unfortunately broken the mini usb connector of my canon tonight, so i am off untill this is fixed.... (too many cables around!)