[APML]: Quantitative drift alignment (was: New Image)

[Reinhard Ilk <ilkr@ping.at>]

The Astro-Photography Mailing List
------------------------------------

An Austrian amateur worked out a method of "quantitative" drift alignment.

He designed a datasheet containing the corrective shifts of the polar axis
depending on the declination of guide star and its drift within 10 minutes
of guiding.

Procedure:

First:
star to the south, 10 minute guiding, measure the drift with an arbitrary
scale (some reticles have one, align in N/S-orientation).
multiply the drift with the factor given for the declination (data from -5
to +5 deg).
rotate your crosshair scale for 90 deg (E/W-orientation) and shift your
polar axis for the calculated value.
Then:
star to the east (or west) and follow a similar procedure.

This is a method for a real precision landing on polar alignment without
"trial and error".
I like it very much, specially for long exposures in high declination
fields.

I'll try to get his algorithm for this sheet because I have only the
figures for +48 deg latitude.
If I succeed, I'll post an Excel-spreadsheet on that.

Reinhard


Chuck Vaughn wrote:

> The Astro-Photography Mailing List
> ------------------------------------
>
> Dave,
>
> Thanks for the analysis. It shows how sensitive the drift alignment
> method is and validates my "5 minute" rule of drifting. No visible
> drift in 5 minutes at 200X or more does give you good enough alignment
> for most any exposure amateurs are likely to do.
>
> I would consider 6 arcseconds of drift in 5 minutes an unacceptably
> large amount with further adjustment required. [...]