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Old 11-07-2019, 08:05 PM
Wavytone (Nick)

Wavytone is offline
Join Date: Jul 2008
Location: Killara, Sydney
Posts: 3,995
Originally Posted by Cliff View Post
The spot seems very central so looks like Collimation is pretty good.
Er... no not true. You need to learn how to do a star test, ie a star approx mag 2, near the zenith, at high magnification (at least 200X) and defocus just a tad. Centre this star in the field of view (this is crucial).

In the centre of the black blob (ie the shadow of the secondary mirror) you should see a bright dot, which is called the "Poisson spot". This is a product of diffraction around the secondary mirror and its useful because it marks the optical axis precisely and isn't affected by changes to the secondary mirror alignment. When the defocussed image rings are concentric with the Poisson spot the scope is collimated.

certainly have light pollution , a Bortle 6
Moon and planets will be fine, also double stars...
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