Re: (IAAC) Problems with Lumicon Sky Vector (and ASTRO)
At 17:34 09/12/97 -0500, you wrote:
>firstly, what scope?
A British made f4.4 20" Dobsonian with a rectangular section open tube. The
tube is made from 4 right angle section aluminium struts from which the
previous owner had cut the 4 previously existing diagonal running braces.
Tube flexure could be a problem but optically in terms of image quality it
is not noticeable.
>secondly, make sure scope is completely vertical or completely level to
>start. (as per instructions)
I have set a bolt in the stand fitted with a lock nut. I set this by setting
the tube struts vertical using a spirit level having levelled the rocker box
to exactly horizontal. A source of error could be that the vertical level in
the spirit level is quite small. How much error can be tolerated in this
The diagonal support is central in the tube to within a couple of mm but it
is possible that the mechanical and optical axes are not lined up well
enough. How can you check this?
>are you using it alt-az?
>thirdly.. practice on lower elevation objects ALWAYS first if you are using
>it in alt-az mode, build up to the zenith last, as it holds the highest errors
I will try that. I had been starting to observe near the zenith.
>also, pick stars approx. 90 degrees apart that are not the same in alt or az.
Again I will do that. I have tried to avoid objects near the zenith for setting
>tell us more
Thanks for your kindness in helping
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Bonnyton House, Ayrshire,Scotland, UK. lat 55 24'56" N long 4 26' 00" W
Altitude 150 m.