PHD Drift Polar Alignment.

[adamsp123]

I spent some time last night between clouds using PHD to do a drift alignment, and by George it works a treat.

Method

- set scope to near meridian and celestrial equator start PHD and do a calibration, start guiding with the DEC turned off, turn on the Graph and change the RA/DEC button to dx,dy.

If you see a steady drift in the dy you move the mount to the East or West until the dy graph remains flat, apart from the seeing causing slight random movement.

Repeat the procedure with the scope to the East or West on the Celestrial Equator, calibrate PHD and guide in only RA, watch the dy trace but this time alter the mount up or down until the dy trace flatlines.

This took me about an hour including longish runs to ensure the dy was really flat.

My Mount was slightly out to the East but a fair way out up/down, now it should be virtually bang on.

The nice thing is you can quickly see the affect of each mount adjustment within a few seconds, especially if you adjust in the wrong direction!

[Glider]

Nice. I also used PHD last night for capturing PEC info as the seeing was rubbish for anything else. A very handy tool. Useful for more than just guiding.

Did you have to orientate the camera in the scope in any particular way to line up the axies?

[adamsp123]

Nice.

Did you have to orientate the camera in the scope in any particular way to line up the axies?

It is sort of aligned but the PHD calibration process sorts the orientation out so to speak.

[Dave Smith]

Very useful idea. Thanks. I will give that a try.

I think I am polar aligned but this gives an easy way to check (and correct if necessary)

Dave

[GrantEb]

Thanks. Will def give this a try.

[lukebl]

Very interesting. I'd never thought of using PHD to drift align. I've used EQAlign till now, but if I've got PHD running, I may as well use it to check on the alignment. Thanks for the info.

[Beyond_Vision]

Very interesting I will have to give this a try

Regards

Kevin

[adamsp123]

Of course this will not eliminate any Cone error you have!

[Dave Smith]

There is probably an obvious answer to this, but how do you turn the DEC off?

I'm using EQmod to contol my NEQ6.

Dave

[adamsp123]

after calibration, stop guiding, open brain, disable DEC guiding, restart guiding as normal without further calibration and DEC should then be off.

[Dave Smith]

Thanks Pete.

Dave

[Tim]

That's how I do it Pete

[davew]

I'm going to have to try that. Thanks for the post.

It sounds like drifting made easy !

Dave.

[adamsp123]

Tonight is the first time I have managed to get some imaging runs going since I used PHD to polar align.

The result is astonishing, the DEC is nearly flatlined and the RA is much better, before I had issues with the DEC oscillating, sometimes wildly, due to the need for constant correction and backlash issues, touch wood that has gone away for good.

[adamsp123]

Update....

I have done a couple more runs of guiding, the correction graph is indeed much smoother with the DEC showing negligible corrections, I do have a little cone error where the DEC drifts constantly in one direction by a small amount only but the smoothness still amazes me.

[IvanT]

Hi,

I've been using EQALIGN to try and get my PA spot on. A recent imaging run showed that my attempt to fine tune it before the run actually made it worse, so I'm interested in giving the PHD method a shot.

One question though & sorry if it's ridiculous.

When doing PA with EQALIGN I've been connecting my QHY5 guide cam to the OTA focuser. My reasoning being that the PA needs to be done on what is being aligned i.e. the mount's polar axis and the OTA runs true to that. After PA is done, I then move the QHY5 back to the 10x50 finder/guider.

My question is this, the finder/guider is not going to be aligned precisely parallel to the now PA OTA, indeed I hear of people adjusting the guider to be able to find a guide star. Does this not impact the guiding adjustments that PHD will be sending?

Or am I just trying to over complicate it, i.e. the drift error is the same whether observed by the OTA of the guider and therefore the same correction is required. It's simply that I shouldn't try to drift align with the finder/guider as that isn't polar aligned?

Thanks

[dc509]

I tried this method and found it worked really well. What, however, is "cone error" - not heard of that before...

d

[adamsp123]

IvanT my finderguider is not exactly aligned to the main scope axis, not far out but I don't think it will create a huge error.

cone error is an error due to the scope not being exactly parallel to the polar axis

[IvanT]

IvanT my finderguider is not exactly aligned to the main scope axis, not far out but I don't think it will create a huge error.

Thanks Pete, I take it I'm correct about using the main scope for the PA though and not the QHY5 on the 10x50?

[adamsp123]

Thanks Pete, I take it I'm correct about using the main scope for the PA though and not the QHY5 on the 10x50?

I polar align using my polarscope then PHD drift align using my finderguider/QHY5 to get it more accurate.

[IvanT]

Interesting, I'll give that a go next clear night I get.

[NickK]

If you take an image through the imaging camera whilst doing the guide drift you'll also check that the imaging sensor isn't picking up error with the alignment of the guider and imaging scope that could cause drift in the final image. Just do a long 5 minute exposure whilst drift aligning.

[mark7331]

Thanks Pete, I take it I'm correct about using the main scope for the PA though and not the QHY5 on the 10x50?

I doesn't really matter which scope you use because you're polar aligning the mount not the scopes. I would just use the finder/guider then you don't have to swap cameras around etc.

Mark

[IvanT]

Thanks guys, this sounds promising and much quicker/simpler than what I've been trying to date. Can't wait to put it to the test.

[IvanT]

Don't ya just love UK weather. Forecast was for partial cloud, great I thought, I should get to try out PHD PA. Things cleared up nicely by 2150, so out I go getting things setup. Peered through the polar scope, low and behold thick clouds rolling in. Patience is a virtue they say.

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