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Drift Alignment in PHD2

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Last Friday was my first time out with a guide camera (Lodestar) and the first time with PHD2. My aim was to use the drift alignment wizard in PHD2 to align my mount and of course to find out a few things along the way. I read up a bit on how to use the drift alignment wizard, but things are a bit abstract until you have a go.

I started by levelling the mount and casually aligning the mount using the mounts polar scope. I then slewed (by hand) the scope to point toward the intersection of the meridian and celestial equator. Then I started PHD2. I focused and then calibrated the Lodestar. I did not change any other settings. So everything was set to PHD2 defaults. Then I kicked off the Drift alignment wizard and thats where the fun and games began.

Despite 2.5 hours of attempts I could not get the graph for Dec or Ra to run level. I could get it to start pretty good but after 15-30 seconds the curve would drift off into the wild blue (should that be black) yonder. Below is my best curve. Not good I think you will agree.

The magenta circle was leaping all over the place, so my attempts to shift the star to it using the azimuth screws seemed pointless. In the end I tried to various iterations until the graph transitioned from pointing up or down. I never managed to converge on a solution.

Can anyone give me the benefit of their experience with PHD2 drift align. What am I doing wrong? I guess I have missed something fundamental?

post-12202-0-19031300-1444158629_thumb.p

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What is the focal length of the main scope and how are you guiding? OAG, second scope ?

The exposure time on the screenshot 0.1s is, i believe, insanely low (could be wrong though, don't have a lodestar :D ) and the camera was chasing the seeing.

Phd2 Manual states : As a starting point, try using exposure durations in the range of one to five seconds.

Give the process a go again after setting it to 2-3 seconds and see how it goes.

Edited by silios
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Yup

Have to agree with silios there.

When I ran DA in PHD2 last I was running with a 2 sec exposure and all was well.

Will be re-running again as soon as the sky stops leaking here (that may be a while) as have replaced my pier adaptor and so need to re-align.

Last time I was at it for about an hour and had fairly straight lines.  This time am expecting it to be slightly less as have done it once so have an idea what to do...although I have slept and drank a lot since then...

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The above is good advice by Silios, The lodestar is very sensitive

but 0.1 is pushing it a bit :)

Try every thing on default and go for a 2 or 3 second exposure, I am

only using Phd v1 but I would imagine the principle is the same

Paul

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i have to admit that i run with very low exposures because i pa at the first hint of a star so i don't think that is the whole answer, i don't know why it shoots off somethings not right!! but i'm looking at the -16 degrees and i'm wondering.....is that correct? are you sure that you are indeed east of the meridian and if so try to get quite close to it but still east!

other than that, it may be a usb issue nothing to do with the pa process but a failure of the guiding outputs..

Ray

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Thanks everyone for your advice. I naively took the defaults and did not consider exposure as the Lodestar X2 seemed to lock onto a star without issue. I will try with a 2 or three second exposure when the skies clear again.

silos, my guide scope is a Borg Mini which has a focal length of 250 mm

libraryman, yes the scope was on the west of the mount. Is that a bad thing when using drift aligning?

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Hi

Ditto re exposure times though 1s might be ok since the trendlines average out the apparent instantaneous drift. Um, I take it you were pointing south-ish when adjusting azimuth? At what altitude? Maybe something causing a severe imbalance e.g. cable drag?

It helps if you're PA is approximately ok to start off with... A funny thing with PHD2 is that it has to be calibrated before drift aligning. (How did your calibration go?) But... I think PA needs to be roughly ok before calibrating (i.e. pointing north, latitude set. A compass App and an App that measures inclination are useful if you're setting up from scratch), as does balance need to be ok. A useful check if you have problems is to just run the guiding assistant first so that you can get a rough idea how the mount is performing. By the way - ignore the RA trendline - you only have to consider the DEC line.

Louise

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Hi

Ditto re exposure times though 1s might be ok since the trendlines average out the apparent instantaneous drift. Um, I take it you were pointing south-ish when adjusting azimuth? At what altitude? Maybe something causing a severe imbalance e.g. cable drag?

It helps if you're PA is approximately ok to start off with... A funny thing with PHD2 is that it has to be calibrated before drift aligning. (How did your calibration go?) But... I think PA needs to be roughly ok before calibrating (i.e. pointing north, latitude set. A compass App and an App that measures inclination are useful if you're setting up from scratch), as does balance need to be ok. A useful check if you have problems is to just run the guiding assistant first so that you can get a rough idea how the mount is performing. By the way - ignore the RA trendline - you only have to consider the DEC line.

Louise

Some good points in this....I was referring to the position of your scope or should I say the pointing accuracy!!! When I pa I always check to make sure that my finder is pointing to the star field that i think is!

I try to pa quite close to the meridian i.e within 20min of it...,say 5 degrees....its important to stay east of it otherwise it can throw of your readings!

My set up is portable so I try to pa very early in the evening and long exposures white out my screen so I routinely start of with maybe 0.05 exposure to get a trend then as darkness falls I increase it to get a bete4 star profile!

I addition to this, I will go over to East to check declination before I spend loads of time on RA .....if the declination is out it will throw RA out when you adjust it.....

My thoughts are that your issue may be that Dec is way out and throwing RA !!!

Just an idea that you might wañt to look at.

Ray

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Had my second play with PHD2 a couple of nights ago. The results were much more predictable with a 1-2 second exposure, so thanks to everyone for your advice. Below is the graph I achieved. The bit at the end where it goes a bit crazy is me messing with the main camera. Unfortunately I only got to adjust azimuth adjustment before the clouds rolled in. One question I have is; if the clouds hadn't have rolled in, is this curve saying I can get guide and would get good results for say a 500 mm FL scope, or do I need still need altitude adjustment, and possibly one more iteration of both az/alt?

post-12202-0-19803100-1444632513_thumb.p

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In theory, you should get as good a PA as you can, and there seems to he room for minute improvement from the numbers down left in phd.

But i believe you could be fine for exposures up to 15 minutes long if everything else plays nicelly.

Give it a go at 5 mins for start, and check results : theories do not always apply in the field :-)

Clear skies!

Sent from my Nexus 5 using Tapatalk

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Had my second play with PHD2 a couple of nights ago. The results were much more predictable with a 1-2 second exposure, so thanks to everyone for your advice. Below is the graph I achieved. The bit at the end where it goes a bit crazy is me messing with the main camera. Unfortunately I only got to adjust azimuth adjustment before the clouds rolled in. One question I have is; if the clouds hadn't have rolled in, is this curve saying I can get guide and would get good results for say a 500 mm FL scope, or do I need still need altitude adjustment, and possibly one more iteration of both az/alt?

Hi

I suggest running the Guiding Assistant (under the Tools tab) for a minute or two. That will give you feedback about drift in DEC and in RA and your PA error (though that seems to be calculated instantaneously so you have to monitor the values and make a judgement...)

Hth

Louise

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