Re: [APML]: Guiding Error Question

[Peter or Marian Robinson <41beaver@vicnet.net.au>]

At 18:10 12/8/97 -0700, Reinhard wrote:
>
>
>Additionally to Chuck's and Anders' remarks you should consider that
>there is no definite maximum error. Regular deviations (e.g. dec
>corrections, poor step motor drives, etc.) can form "eggs" at a guiding
>error of only 20 to 30% of the disks diameter whereas casual errors like
>a sudden wind gust won't leave a trace even if the error is several
>times the circle of the smallest stars. The smaller ones wouldn't record
>the short deviation, the brighter ones have a considerably larger
>diameter. Thus, 5 minutes pictures have to be guided more carefully than
>long time exposures, because the "percentage" of a casual guiding error
>is higher.
>
>Reinhard
>ilkr@ping.at


This raises the question of the SHAPE of the disk showing deviation.
Uncorrected regular deviations (eg periodic error) might produce elipses
whereas delayed correction on the dec axis might produce teardrops (squashed
elipses). Either way what we would notice in the final print is variation
from a circular image. Has anyone tested the limits of observers' capacity
to distinguish between circles and elipses as the ratio of major to minor
axis increases (ie the disk becomes less circular and more eliptical)? I
have a gut feeling that this may be somewhat independent of magnification.

Peter
37 27'0" S 144 58'12" E