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PHD2 Guide Accurcy


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So last night i had a go at guiding for the first time, i have a number of issues.


1) I found that 2 ports on my USB hub were dodgy.

2) i found that if i used my USB extension cable my mount wouldn't connect to PHD2 and i got warnings about pulse guiding / moving on PHD2. But it would connect via ASCOM and Strellarium and work fine.

3) i ran through the setup wizzard again, cleaned the lens on my scope helped and then making a new set of Darks for the guide scope. i also tried as best as i could manage to focus it (thanks Mars).


when i managed to get everything connected (via a spare USB hub plugged directly into my laptop not using the extension cable) i got readings from about +/- 0.5 to about 6 arc seconds on the graph, i only wish i had taken a screen shot to share, its no where near the +-0.5 to 1 arc second i have seen.


I did buy the mount a year old second hand form someone whos dad bought it for retirement and then sadly passed away. It was quite obvious that its not had a day or night outside, there wasn't a mark on it, and it has the rowan belt mod, which i have checked and that is fitted. There does seem to be a bit of wobble in the bearings; i can get hold of my scope and i get about 1-1.5mm of stationary bearing wobble, im wondering if i need to go as far as strip clean and grease it at this stage?


Also i see when i look at a 10 second test image i took in processing software the histogram RGB doesnt align on to each other, is this normal, i figured having a triplet scope they would align perfectly?




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22 hours ago, Kevin17 said:

im wondering if i need to go as far as strip clean and grease it at this stage?

No don’t do that as it won’t be necessary. The wobble or knock in an HEQ5 pro is caused by the worm gear not being fully engaged. It is very simple to fix and if you follow this guide you will be ok https://www.astro-baby.com/astrobaby/help/rebuilding-the-skywatcher-heq5orion-sirius-mount/adjusting-worm-gear-engagement-motor-gears/

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The lack of "alignment" of the RGB components isn't anything to do with your telescope optics.  Its simply that the camera has a different response for each channel.  You just need to adjust the white balance by increasing the gain on the blue channel. It'll be in the manual somewhere. The stars in your image will then appear white rather than the current yellowish tinge.  This assumes that the bright objects are predominantly white.


Anytime I have a problem with guiding, I always check that the gear clamping screws are firmly tightened. They have a habit of working loose.  In my experience this method of clamping gears to shafts is rather unreliable, but unfortunately widely used.  I always drill and tap an extra clamping screw in the hub to double the clamping force, which seems to fix the problem  Sometimes these grub screws are just too small to begin with.  The flats on the shaft don't make the clamping any more secure - they're just to stop the burrs thrown up by the screw from jamming the hub on the shaft.

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  • 3 weeks later...

When you have fixed your bearing problems. The best procedure for good guiding is a level mount, polar aligned as perfectly as possible. Calibrate the guiding in PHD2 by pointing the scope South close to the intersection of the meridian and the Celestial Equator. Once calibrated, run the guiding assistant, make sure measure Dec backlash is checked. Run the guiding assistant for 8 or 9 minutes. Then apply the settings it suggests.

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I have an HEQ5 and when I started guiding using PHD2 I had a lot of problems with things dropping off the USB hub that I use. I use CdC, PHD2, APT. PHD2 would lose connections to the guidescope, APT kept timing out and CDC would lose connection with the mount and so on and so on. It seemed like the hub was acting like a bottleneck to USB comms.  I'd kick off a series of image gathering on APT and it would fail after 10 or 15 minutes. Very frustrating.


The problem was finally solved by getting a new 13.5v power supply for the mount.  So now I have two power supplies. A 13.5v supply for the mount only and a separate 12v supply for everything else and I now it's been working fine for the past year.  I was put on to this by a reply on another forum who told me that the HEQ5 need a good 14v supply for the comms to work correctly. I couldn't find a 14v but I ended up with the 13.5v supply and that seems ok.

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