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Fordos Moon

HEQ5 Mount - Never drift guided - should I do this?

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My HEQ5 is pier mounted.

I do a polar alignment each time I swap scopes on the mount, (not that often) then I do a 2/3 star alignment using the handset, then set up PHD2, then start capuring my images using BackYardEOS.

I think my stars have been pretty good today with up to 7 minute exposures (I've attached a couple).

But I have never drift aligned and having read this forum I am wondering should I?!

I found this link - http://www.cloudynights.com/page/articles/cat/articles/darv-drift-alignment-by-robert-vice-r2760

...which looks straight-forward but note it says it was done for a fork-mounted scope.

What does one do, particularly in the light of going to CCD (longer exposures) next year?

7 minute exposures:

post-26268-0-91534900-1415181721.jpg

5 minute exposures:

post-26268-0-76136800-1415182012_thumb.j

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From these pictures, it seems your mount is doing rather well but it's hard to say...

We'd need to see some 100% crops (at near pixel-resolution) and a PHD guiding graph to say.

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From these pictures, it seems your mount is doing rather well but it's hard to say...

We'd need to see some 100% crops (at near pixel-resolution) and a PHD guiding graph to say.

Thanks mike, much appreciated I will work on the images to add here. My PHD graph does contain a few ups and downs on occasion, usually "1"s on the blocky columns but horizontal line maybe up/down 2mm up and down. (sorry i cant do technical speak!)

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If I had my HEQ5 on a pier I would drift align it and do it again every now and again for sure, just because it would be worth the effort, as it would be all ready and the best I could make it. I have tried it once to see what it was like to do but as a setup/teardown person at the moment, I can get good enough polar alignment and PHD guiding for my needs (10 min subs at moment) without the extra steps it takes.

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I would, if you drift align w/ PHD itself, doesn't cost too much time, and one gets good results.

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I would, if you drift align w/ PHD itself, doesn't cost too much time, and one gets good results.

Ooh wasn't aware I could drift align with PHD itself - is it straight forward Andy?!

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Hi,

Looking at your images, I would leave alone at the moment, as drift alignment is quite hard to master initially, but once mastered it is easy and an excellent tool.

If you do it and things don't go quite right, you may kick yourself.

Like I say your images look excellent at the moment so, if all is working ok and not broke, done fix it......:)

This is only my opinion though

SS

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I don't drift align simply because I go to a dark site and image remotely although this is something I need to get my head round. I think its only PHD2 which has the drift align option.

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You can use PHD1 in the same way but it's been nicely packaged as a process for PHD2.

I think the DARV method is excellent for getting a rough alignment. After that there is no reason to feel it's any better than normal drift because, after all, that's what it is. It's just that the vee graph it creates during the drift is very easy to interpret. I'd probably go for PHD2 these days, or DARV for two iterations then PHD2.

There may also be a case for imperfect PA. It can be an advantage if you have some Dec backlash, as is common enough. Whereas with RA you can use a weight offset to hold the mesh to one side of backlash (run east heavy) this doesn't work in Dec because at the zenith your weight offset vanishes since the OTA is vertical. So if you have a slight polar misalignment you can set your Dec corrections to work only in the direction needed to correct for misalignment. You can disable the other Dec direction and reduce oscillations across backlash. Also the slight rotation induced during a run can act as natural dither in noise reduction. So I'm not averse to a small amount of polar misalignment. Repeat, small!!

Olly

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As Olly says above and the PHD2 output gives you your error in arc seconds. The graph in PHD2 shows my Dec axis oscillation quite well or not so well actually but it does mean I can choose to apply the unidirectional correction Olly describes. There is an RA/Dec overlay on the screen so you can work out North vs South and make your choice. I usually do the Synscan PA routine to about 30" which takes 2 iterations then apply the PhD2 drift align and for my mount the best I can hope for is about 15" although I have got it to 8". This probably gives me dither as my frac rig works at 1.25 arc seconds per pixel?

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Hi Fordos

I see Chris already gave you a link, just in case, here's my process, distilled.

The mount has to be well leveled (so as not to introduce, or introduce as little error as possible; when you correct the drift in one axis, if the mount is not well leveled, it will introduce a small error in the other axis.

Rough Polar alignment, where I visually put Polaris in it's correct position on the circle in the finder scope.

I then do a 3 star alignment (one can also do a 2 star one for the drift, and after drift, the 3 star one). By now I've done it so often that, even w/ crude visual initial alignment, I come pretty close to where I need to be).

I then slow to the first star (AZ)

- calibrate PHD

- once it guides, stop guiding, and turn off dec. guiding

- switch on the graph to dx dy (not RA/Dec)

- capture and "guide" (with Dec guiding off)

- watch the dy (red) line on the graph, see how it drifts

- turn off "guiding", make your correction on the AZ knobs of your mount (if you don't know the direction, try one, you will soon see whether it was the right or wrong one)

  The idea is to bring the red graph line to the center line, and have it even out.

- Make these corrections until the graph line is flat (after each correction, capture and guide again to see where you're at, and stop when you make the correction).

- Once happy, clear graph, and slew to a lat. star (as close as possible to the 6 or 18 o'clock position, what I do, if my star is slightly East of the Meridian, I slew to a 2nd star in

  the same direction, i.e. East)

- turn on dec. guiding, and fully calibrate again

- once guiding, turn dec. guiding off, and follow the steps above, until the graph is flat.

That's it ( I do 2 iteration for AZ and Lat. each, just to be more precise and cut down on possible errors, which you can see by the red line (dy graph)

Andy

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Hi Fordos

I see Chris already gave you a link, just in case, here's my process, distilled.

The mount has to be well leveled (so as not to introduce, or introduce as little error as possible; when you correct the drift in one axis, if the mount is not well leveled, it will introduce a small error in the other axis.

Rough Polar alignment, where I visually put Polaris in it's correct position on the circle in the finder scope.

I then do a 3 star alignment (one can also do a 2 star one for the drift, and after drift, the 3 star one). By now I've done it so often that, even w/ crude visual initial alignment, I come pretty close to where I need to be).

I then slow to the first star (AZ)

- calibrate PHD

- once it guides, stop guiding, and turn off dec. guiding

- switch on the graph to dx dy (not RA/Dec)

- capture and "guide" (with Dec guiding off)

- watch the dy (red) line on the graph, see how it drifts

- turn off "guiding", make your correction on the AZ knobs of your mount (if you don't know the direction, try one, you will soon see whether it was the right or wrong one)

  The idea is to bring the red graph line to the center line, and have it even out.

- Make these corrections until the graph line is flat (after each correction, capture and guide again to see where you're at, and stop when you make the correction).

- Once happy, clear graph, and slew to a lat. star (as close as possible to the 6 or 18 o'clock position, what I do, if my star is slightly East of the Meridian, I slew to a 2nd star in

  the same direction, i.e. East)

- turn on dec. guiding, and fully calibrate again

- once guiding, turn dec. guiding off, and follow the steps above, until the graph is flat.

That's it ( I do 2 iteration for AZ and Lat. each, just to be more precise and cut down on possible errors, which you can see by the red line (dy graph)

Andy

Fastastic! Thanks Andy will give it a go whenever the sky decides to be clear again!

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