[ATM] spider rotation

[Dale Eason]

The placement of the secondary is not that critical
assuming it is collimated.  All that happens is that
the secondary will not catch the full image of the
mirror and some vignetting will happen.  For visual
that is not important the edge of the image will be
darker but you will not notice it until it is about
1/2 as bright.  For imaging it is more important so
what is usually done is that the secondary is sized
larger to catch everything.

It seems to me that you are worrying about something
that is not an issue.  That is why you do not find any
plans for what you think you require.  I know of no
design that tries to keep the diagonal centered while
adjusting it.  The movement of the center of the
secondary away from the optical center is going to be
very small because it does no move much during
collimation.

The common spider that everyone seems to use seems to
be good enough for everyone else.

Dale Eason


--- Jerry Hillman <truckeratm at sbcglobal.net> wrote:

> Hi All,
>   Can anyone direct me to a site that has built a
> spider that is not a variation of the common spider
> that everyone seems to use. Since the placement of
> the secondary mirror is so critical, I am looking
> for a design the uses the surface, center of the
> mirror as the rotation point, not the tip of a
> adjusting bolt that on my scope places the rotation
> point about 3 inches away. Makes for a frustrating
> time trying to adjust the mirror since centering the
> mirror moves it out of collimation and collimating
> it moves it out of center. I have about 1/8" offset
> but same problem applies. I can provide drawings
> that illustrate my problem.
>   Jerry
> _______________________________________________
> ATM mailing list http://www.atmlist.net/
> 



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