M81 + M82

[gonzostar]

Hi

Dispite it being full moon time  Tuesday Wednesday evening I thought i would practice my autoguiding. So choose these two as they are brightish objects as far from moon as possible. and high up.

Seeing conditions were not great, also high thin cloud on Wednesday.  Despite this autoguider managed to find a guide star. 

Overall 60mins of 3 minn lights where taken with dark, flat and bias frames. Did not want to expose more the 3 mins as each sub was getting to bright according to blue channel on histogram from camera

Used Canon 450d (unmodded camera) with CLS filter. With the ES102mm APO refractor on AVX mount

Stacked with DSS and processed using PS

On Tuesday night I did the guide assistant told me RMS error was 13 arc mins, on Wednesday  was 8 arc mins. What value do people say thats to high and re-do polar alignment? i used the QHY polemaster

What value do you use for sidereal time? is 0.75 to high? Doesn't seem to much different at 0.5

Guiding starts off great for first couple of minutes then DEc wanders off. Phd2 unable to catch up. Did assisstant and told me to put min-mo to 0.1 for both dec and RA.  I disagree with this is this to low. Hysteresis setting 25 (to high?) 

Or could this be the effect of seeing conditions of the night or flexure issues? I make sure everything is set up tight. The I have cable to a minimum ST-4 cable,  cables camera to laptop cables

Anyway any help, suggestions gratefully accepted

Thanks for looking

Dean

 

 

[Graham Darke]

Dean,

When imaging I usually aim for a polar alignment error of less than half an arc minute in both axis. I'm not familiar with the Polemaster but you might want to check that it is square on to the polar axis. If it not square on then it will introduce errors. You can check its straight in the daytime by pointing your polar axis at a distance object and observing any drift as you rotate the polar axis of the mount from one side to the other. As for the guide rate I always use 1 x sidereal with PHD. 

Hope this helps and good luck - that seems to help with imaging too ? 

[Graham Darke]

Polemaster is not what I thought it was. Ignore me. Hopefully someone who has one will be able to help you. 

[gonzostar]

Thanks for your response Graham . I have checked the base plate of the polemaster to the mount and was slightly not level. Which could explain some discrepancies. So thanks for that tip which i overlooked  However difficult to judge on Avx mount .

On the phd2 graph i can get fluctuations up and down to 3 arc secs. To me i dont think to bad as my exposures are upto 3-4 at a push 5mins subs. Due to LP around my area.

I will set sidereal to 1, i have being using 05-075

Hopefully this will improve matters 

Dean

 

 

[gonzostar]

Is there a way from the shape  of the graph on PHD2 identifying if its PA error of backlash? 

 

[gonzostar]

or flexure issues?

Cheers 

Dean

[wimvb]

Nice image, Dean. You've come a long way, and it seems that the new scope is a joy to image with.

As for analyzing phd curves, have you seen this tutorial?

http://openphdguiding.org/tutorial-analyzing-phd2-guiding-results/

There are also (free) programs out there that can be of help.

http://openphdguiding.org/phd2-log-viewer/

If you google 'analyzing phd2 guiding', you should get several usefull hits.

Good luck

[gonzostar]

Thanks Wim as ever for your words of encouragement. The new scope is a delight to use. Wish i had bought it earlier. Its certainly  "easier" to guide then the SCT. Once guiding gremlins sorted i can focus on better processing

The links are very useful. I did also read this link from yor links

 http://openphdguiding.org/Analyzing_PHD2_Guide_Logs.pdf

It seems alot of peak and troughs come from seeing conditions. Also making sure things are properly tight and no dragging cables. I can get initial polar alignment with in 10arc secs. PHD2 guiding assistant doesnt seem to grumble to much about that.

However maybe i should use the drift alignment tool in PHD2 to improve. However clear moonless sky are rare these daus here.

Cheers

Dean 

[wimvb]

I think that 10 arc seconds polar alignment is very good. But you can always check with PHD guiding. I find it very easy to use.

When I started with guiding, I used Lin_guider, which is actually simpler to use than PHD. Lin_guider has the opportunity to average a number of frames before a guiding pulse is sent to the mount. This meant that even with a 1 second exposure time for my guiding camera, I could apply guiding pulses every 3 or 5 seconds (by averaging 3 or 5 images). This is a great way to avoid guiding on seeing. I haven't found this feature in PHD yet. Otoh, PHD seems better at guiding.

One thing that can cause flexure in your setup (besides anything that can be loose), is the heavy DSLR hanging from the focuser. It can bend the whole OTA, or just the focuser draw tube. This can be difficult to avoid.

[gonzostar]

A small minor positive last night i had a 2 hour or so gap of no clouds. Despite what met office forcast said Seeing was not good though, but would give everything ago.

Anyway tried my luck at the the black eye galaxy which had just gone past the meridian at this time. and guided away. Again everything fine for a couple of minutes. Within 1-2 arc secs fluctuations. 

Then the gremlins attacked! Dec kept wandering off. Did clear blacklash bit better maybe need to repeat this process again as phd2 requested. Also said my min-mo should be down to 0.1 which i think is a bit low

Also thought about what you said about the weight of camera. When i set up the scope in dec i can get it balanced. Would you think that making this axis camera "heavy" may make a difference? I do slightly inbalance RA east heavy. RA seemed fine last night. 

Dean

[wimvb]

That seems odd. Even an imbalance i dec shouldn't give the kind of runaway that you describe. It seems almost as if dec guiding was turned off. I usually have my setup as balanced as possible. I have virtually no RA backlash, and decreased DEC backlash as much as possible. I start guiding a while before I start imaging. During that time, if I see strange DEC behaviour, I turn off first DEC+ guiding, and then DEC- guiding, to see to which side I should guide. I then put DEC guiding to this side only. But many times I can have both DEC+ and DEC- guiding on.

Sorry, can't help you more than that

[gonzostar]

I think i have tons of DEC backlash. Maybe initially do manual guide north as suggested in PHD2 manual. Then run guiding assistant a couple of times before snapping away. 

Another alternative maybe is not to have guiding on at all for the first couple of minutes. Then turn it on let it guide before the gremlins come  Then i have a 4 minute picture!