VintageBigBlue.org

 

Polar alignment ritual, and a new way to screw up...


May 14, 2001

 


----------------------------

#4082 May 14, 2001

I would like to double check the polar scope/polar alignment rirtual

with folks here.



Polar scope ritual



The only basic "trick" of which I am aware is this: when Polaris moves

UP in the fov, the mount/scope are moving DOWN: DOWN means that it

might catch momentarily on something, while you align, and then settle

more, till it hits the adjustment screw. If the settling occurs

*after* you think you've aligned you will perceive it as a setting

circle problem, but really you're being told the mount shifted.



So, after I have gotten everything neatly in place (Polaris and 2ndary

star), I look through the scope and do an altitude adjustment to make

Polaris move to edge of field UP, which moves the scope/mount DOWN.

Then I adjust in altitude to move polaris down (scope/mount moving UP)

being very careful to ease oh-so-slowly into that final spot so that

the mount, moving UP, is resting against the screw, and gravity works

to maintain the adjustment.



The problem...



Last night, I had a devil of a time, because every time I moved the

scope the polar alignment would be lost. This occurred even with

everything tightened down hard. After about an hour things seemed to

work better, not perfectly, but better, so disgruntledly and

perplexedly I concentrated on observing. (I'll post that on sct-user

at some point). To be brief, things worked out OK: a night in which

the dscs helped me locate some 14th mag galaxies and Pluto (!!!) can't

be characterized as bad. But I was stumped as to why it took so long

to get the mount to "hold" polar alignment.



The cause??



Sooo....what was going on??? I finally realized that in the past few

weeks I have adopted the custom of using a rug while observing. It's

great, gives you a place to spread stuff like books under the mount,

cleaner, nice, etc. Works FINE on the driveway, and protects

eyepieces when dropped. During my first few runs out of town, I had

the rug, but I set it up NEXT to the telescope not UNDER it. The

reason being that my wife and child and I were picnicking.



Last night, sans wife and child, I figured I could hog the rug to

myself, and put the mount/scope ON the rug ON the grass. I now

realize that as the weight shifted the mount on the rug on the springy

grass shifted. The rug spread the weight out and acted like a snowshoe

does on snow, keeping the mount from doing what it ought to do, which

is dig in hard and get firmly placed. After about an hour of

frustration, I hypothesize that the grass was getting squished enough

for the problem to abate. The problem was mostly in Alt but some in

Az, consistent with what you might expect as the SE and SW legs (I try

to keep one leg pointed N)shifted a bit, causing mostly Alt but some

Az shift.



This is the only reason I can think of why a system that worked fine

on Thursday had problems on Sunday, and why it got better after about

an hour. In a way, I know how to use a G11 mount, but I haven't

learned how to "think" like a G11 mount. I have a tendency to assume

that a "problem" is with the mount, and sometimes it is; but operator

error has proven to be a significant factor with this equipment, I say

it candidly, thinking perhaps that others have had similar

experiences.



greg nowell



Contact Us
This Site's Privacy Policy
Google's privacy policies

S
e
n
i
o
r
T
u
b
e
.
o
r
g