Mike Shade

PHD Drift Align wizard does a classic drift align that minimizes only Dec drift over most of the sky. However, that results in significant RA drift at the zenith. Drift in RA increases the further south you live. Why is this the classic drift align? It was developed this way because in times past most equatorial mounts had only right ascension drives and no way to adjust declination drift. If you could eliminate Dec drifting, then all you needed was a drive corrector for the RA motor that would allow you to adjust the right ascension drive rate to compensate for the RA drift, and you had a fairly nice unguided system and could take images.

The modified drift align that I suggest is as follows: do the classic Dec align at the celestial equator/meridian using the azimuth knobs. Then do the RA drift at the zenith using the altitude knobs. What you will end up with is no RA and no Dec drifting at the zenith. This near zero drift zone will extend approximately 30 degrees in either direction, giving you a 4 hour drift-free window for imaging. Depending on focal length and pixel scale, you might get round stars in a typical 10 - 20 minute exposure as much as 45 degrees from the zenith.

So, you can do drift align either way: align on the pole with PHD or align on the refracted pole with my method. First one will minimize Dec drift over a large area of the sky, them second one will minimize RA and Dec drift at the higher parts of the sky where most imaging takes place. Everywhere else you will need to guide.


This is interesting. A couple of clarification questions:

Drift near 0 dec/meridian adjusting E/W-azimuth to minimize DEC drift, east of meridian. I have the "classic" instructions if it drifts N move E and so on...Assume that these apply.

Then go to near zenith, E of zenith. Is one watching for DEC drift here as well? I would assume so as RA will have some PE thrown in. Any idea what the motions are if it drifts N axis is high or...? With a long FL and heavy scope this will help instead of floundering around.


-----Original Message-----
From: [ap-gto] <>
To: ap-gto <>
Sent: Thu, Nov 2, 2017 10:35 pm
Subject: [ap-gto] Re: AP MACH 1 CP4 GUIDING RESULTS


When you say "RA drift align", is that when we adjust the Azimuth or Altitude knobs?

PHD's Drift Align wizard first points to the meridian and celestial equator and has us turn the Azimuth screws, then points west and has us adjust the Altitude knob. It doesn't say which one is adjusting RA and which adjusts DEC.


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