Re: [ATM] spider rotation

[fundo@bellsouth.net]

From: Jerry Hillman <truckeratm@sbcglobal.net>
>
> 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, 
The best solutions are always the simplist.   If everyone uses them, then they must be pretty good.  The main variation that I see is the wire vaned spiders.  What you are asking for is mechanically....difficult or "clumsy".  

It sounds like you need to make sure secondary is centered with the vanes (this includes any offset).  The collimation can then be attained by moving the holder in or out (along the optical axis), and tilting with the adjusters.  You need three lines of movement and this would give you all three.

I build wire spiders for my telescopes, and I always center the hub.  Any offset, I build into the diagonal holder.  You will need a curved surface with the radius centered on the center of the mirror to effect the tilt of the mirror in your idea.   You would only be able to get a small amount of tilt (not that you would need much if it is built correctly) if the surface of the mirror is as far back as you say from the piviot.

*****-----
Dan F.
Memphis, TN 
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