Setting up PHD with CG5-GT and Finderguider

[Anweniel]

Anyone using/used a similar set up to mine can suggest where I am likely to be going wrong?

I have a QHY5 connected to a Celestron 7x50 finder to make a finderguider. This is connected to the CG5's ST4 guide port and the USB cable to my laptop. I have setup the ASCOM platform on the laptop and have run through the calibration process a couple of times with it going through ok.

Couldn't achieve anything satisfactory on a really calm cloudless night. Even @ 1 minute the exposures are not great

The process I run through is this:

1) Take the mount outside and plonk it roughly towards the celestial pole.

2) Use the polar axis scope to align Polaris (currently with Cassiopiea)

3) Attach the scope and check balance on both axis slightly weighted camera end.

4) Do a 2 star align followed by 2 calibration stars close to the region I am intending to image.

5) Set GOTO to my intended target.

6) Initalise PHD and begin calibration procedure.

7) Once PHD finishes calibration, commence imaging session.

Calibration tends to complete ok but shortly after commencing guiding the software starts flashing and beeping at me which I understand means something has gone wrong with the guiding (evident in the subs)

Do I need to setup the CG5 on the ASCOM platform? This one thing I haven't done - assumed the ST4 port just did everything from the QHY5 signal.

One thing I have done is 'firmed up' the finder bracket - using the WO 50mm bracket which felt like the foot was very secure on the focuser but the pillar had a bit of movement so I have tightened the screw holding this with some grips.

Any help or advice is much appreciated!

[RikM]

If you are guiding via the ST4 port, you want to select 'on camera' from the mount menu. With a finder guider, the calibration step, needs to be longer than the 750ms default setting otherwise the star won't move far enough for calibration to be effective (due to the short focal length). Other than that, you should be good to go.

It only really 'dings' and flashes at me when clouds get in the way and it looses the guide star.

[Anweniel]

Thanks Rik, I didnt want to leave it until a rare cloudless night when I am getting frustrated to ask! I seen other threads on PHD suggesting longer calibration steps but it seemed to go through that ok. I shall take your advice and up the step maybe double it??

[msh1]

when you say" Use the polar axis scope to align Polaris (currently with Cassiopiea)" are you putting polaris in the little circle

[Anweniel]

when you say" Use the polar axis scope to align Polaris (currently with Cassiopiea)" are you putting polaris in the little circle

Yes, I am sure polar alignment isn't too far off and I understand that exact initial alignment is not imperative because obviously the guiding will make up for it being a little off. Also the GOTO is getting the framing of my targets pretty close to spot on central so I have some confidence this is ok.

[msh1]

sounds like polar alignment i was having similar problems i now use the date and time setting dials to get polaris spot on i can now get 10 mins exposure the software in the handset should sort out miss alignment though, its worth a try

[Anweniel]

Thanks, I know some people don't even use a polar scope, just look through the gap and make sure Polaris is in the FOV then use the star alignment process to fine tune the PA. I suspected it was more the PHD settings, if Riks suggestions don't sort it I'll be sure to check my PA again, many thanks for your suggestion msh1

[Anweniel]

Thanks again RikM. Changing the calibration step really worked and the guiding was sweet Saturday night for over 10 mins

Having not changed anything Sunday night was massively disappointing with only 1 minute exposures being useable... the seeing was about the same maybe a touch worse Sunday with some wispy high cloud too. I noticed that although the graph on RA is pretty peaky, the general trend is toward 0, however the Declination is steadily wayward.. my immediate instinct is a problem with balance? I shall double check this anyway.

Here is an image of Saturdays guide graph:

Sundays graph I didn't screen grab but suffice to say the Declination gradient was much steeper and disappeared off the graph very quickly. So I made the connection between the poor guiding and the change in the dec graph. Tried shifting the scope slightly along the dovetail, recalibrating PHD , redoing the PA all to no avail and I gave up on it.

Having got up this morning I noticed the declination cable wrapped around the Declination housing! hmm seems this may well have been the issue? Drag on the dec axis from the cable pull?

Or is there another issue I may have had? Any ideas/advice greatly appreciated

[Anweniel]

i now use the date and time setting dials to get polaris spot on i can now get 10 mins exposure

All sorted now and it seems you were also right about the PA!!!!!! I discovered the time scale was catching slightly when the latitude scale was locked throwing the alignment out, I did a PA and adjusted the RA by eye so it was in line with the Cassiopeia etching and what a difference to the dec guiding! heres my new graph:

Thanks again for the help guys

[msh1]

wow i got something right

[RikM]