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Eq N 2 Star Align, Polar Align, and Drift Align

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#1 JayTee

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Posted 18 April 2013 - 01:39 AM



Hi All,

Last night was the first clear night available where I could plug everything into everything. CPC1100 on the Pro HD Wedge. Meade 102mm Guide scope on top of the CPC 1100. Canon T1i attached to the CPC 1100. Logitech QuickCam Pro 4000 attached to the guide scope. Everything counter balanced. CPC 1100 and Logitech RumblePad and all cameras attached to my laptop.

Side note-the two previous clear nights I took just the CPC 1100 on the wedge out to practice an Eq N Two-Star Alignment followed by a Mount Polar Alignment (old terminology-Wedge Align, where you physically move the latitude and azimuth position of the wedge on the tripod) finishing with another Eq N Two-star alignment. I did not accomplish a drift alignment at this time.

So last night I did the same procedure of the Eq N Two-Star followed by the Mount Polar Align followed by the second Eq N Two-Star alignment. For extra measure I threw in a 2nd Mount Polar Alignment followed by a 3rd Eq N Two-Star alignment. Very little adjustment was necessary on the 2nd Mount Polar Alignment which led me to believe that a drift align wasn't necessary!

Fortunately everything talked to everything (it was really exciting). I was using different guiding programs to see which one I liked best. I started with PHD, followed by GuideDog, then GuideMaster and lastly MetaGuide. I also messed around with ATP and decided it was worth the $$. I was using Regulus as a practice guide star (as it is bright) and all 4 programs seemed to guide adequately for at least 5 minutes (that was the test duration). Both GuideMaster and MetaGuide during the calibration routine were telling me that the corrections it had to make to keep Regulus centered were quite large and indicated that I needed to do a drift align to further refine my mounts orientation to the NCP. Although both programs seemed to be able to guide on Regulus. I'm sure that PHD and GuideDog were telling me the same thing, it just wasn't apparent to me.

So long story long: are these all the steps, do the Eq N 2-Star align followed by the Mount align then another Eq N 2-Star align then the drift align ending on a 3rd Eq N 2-Star align, to get the desired AP precise alignment?

If this is true, there's no such thing as a quick AP setup...

Thanks for reading all this and clear skies,
JT

#2 Cliff Hipsher

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Posted 18 April 2013 - 06:50 AM

JT:

You're correct. There are easy ways and there is the right way.

When you get down to the nitty gritty, a drift alignment is the most accurate form of polar alignment, but even that is based on using your MK 1 Mod 0 eyeball.

On the other hand the purpose behind using a guide camera is to to compensate for mechanical errors/imperfections within the mount like Periodic Error, tracking motor speed fluctuations, improper gear mesh, gear backlash, and so forth.

One other thing of note is that if only you do a drift alignment with no electronic alignment, more than likely GoTos will be out in left field.

The reasoning behind this is even if physical the Polar Alignment is absolutely perfect, the Goto computer does not have a clue where it is physically located, or what the local/sidereal time is. Without that data, the computer cannot determine how far and in what directions(s) to slew the optics and arrive at a given object.

#3 cn register 5

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Posted 18 April 2013 - 02:01 PM

I've a slightly different approach, basically it is:
Align - a 2 star or 2+3 or 4 on a GEM
ASPA
Image

I'm not expecting perfection but what I get is an alignment - including a polar alignment - that's good enough that the guide camera can cope.

If tried to do the full monty it would probably be cloudy before I'd finished.

Must rush - it's clear!

Chris






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