Hi guys, this is probably going to be a long post as I have a few questions, and I feel I have to explain my process so someone out there might be able to tell me where I am going wrong.
First my Setup:
Mount: HEQ5Pro (with belt mod)
50mm guidescope and ZWO Asi 120mm guide camera.
Canon 1200D (no mod) and 50-250mm Lens.
Software:
PHD2
Stellarium
Astrophotography Tool
I've only had the mount about 6 months, and have got my setup to a point where I can be setup and shooting in around 30min with polar alignment that's "good enough" for my current setup. (around 1.5-2.5 arc/sec/pixel. I believe my image scale is around 3-4 arc/sec/pixel with camera and lens setup). at either rate I don't see star trailing in my images so I'm content with that for now.
However I'm looking to get this tracking down to consistently under 1.5 arc sec as I want to upgrade to an ED80 or similar refractor. (I believe the image scale with this kind of scope and dslr will be in the 1-2 arcsec range )
Problem 1:
I polar align using the drift align in PHD2. However I find it quite difficult some nights to sneak up on a good polar alignment. And I'm not sure if it's due to the seeing conditions or some other issue.
So when doing polar alignment I pick a star near the celestial equator up high in the sky. do the drift align and make adjustments to the azimuth of the mount. Now at the start of the drift align, the PHD2 graph is generally 30arc/sec or more of error and will even out to a lower number. Once I know its still not close enough I make adjustment. Now an example of my problem is this. say PHD2 tells me I'm off by 6 arc/sec. I make a small adjustment (in the right direction
). then run the drift align. Now it says I'm 10 arc/sec out in the complete opposite direction! And if i run the drift again without making changes it could be different again.
Why do I get such variation when trying to drift align? I understand it takes very small adjustments once your down around 5 arc sec. (like just tightening the thumb screw can be enough to change things).
But is this zig zagging of being close to alignment make a minor adjustment and being wildly out, just a function of the seeing conditions? focus on the guide camera? (I believe focus is good on it and everything is mounted very tightly) or some other factor?
Problem 2:
When guiding, my mount will sometimes encounter (more so in the dec axis than RA) large blips in the accuracy of the guiding. I can run at say 3 arc/sec guiding (peak to peak) but then get areas where I could go to 5-6 arc/sec peak to peak. Some times there can be minutes of wildly fluctuating in both axis. (big spikes in both directions on the graph on both RA and DEC). Is this due to some issues with belt tension on the motors? misalignment on the worm gears? seeing conditions? I feel like it could be an issue with misalignment on the worm gears as after a few minutes things generally settle down and guiding returns to acceptable levels again.
I also have a problem where PHD2 will stop tracking. It just starts throwing full strength pulses on the RA axis but the graph doesn't respond and the guide star starts to drift in the frame from the guide camera. After I reset the guide camera pick a star again, sometimes it will work fine again. other times I basically have to disconnect all software and reopen to get it working again. (This is killing me once I'm setup guiding and leave it to run a set of shots only to come out and see it stopped guiding 10min after I left).
Problem 3:
Do I need to calibrate PHD2? I have read about the calibration process for PHD2. but haven't tried to sit down and complete it. Is it necessary? what is its function in the guiding system? And is periodic error correction worth using with PHD2?
Problem 4:
There are 2 sets of arc/sec guiding values PHD2 gives you. one is the RMS and one is the peak to peak error.
as mentioned above my peak to peak error is somewhere between 2 & 4 arc/sec depending on the night. However my RMS is generally well withing 1.25 arc/sec. and Total RMS is always under 1 arc/sec with an oscillation around 0.3-0.5.
I thought I read that RMS number around what I have is perfectly acceptable for my kind of mount. However I believe my peak to peak error can be alot better. Any information on what these values "tell you" and how they relate to the guiding is appreciated. Just so I understand whats going on a bit better. (my understanding is if the RMS is accurate that most of the light of the star will be collected towards the centre point of the star. and the peak to peak identify's the outer boundaries of the star. ie how bloated it is).
I think if anyone can help me with the above it will make my nights out observing so much more pleasant
I don't have any guide graphs to post here at the office but I will try and upload some tonight when I get home.
Thanks in advance.