Re: ATM Re: string spiders

["Jim Miller" <jim@jtmiller.com>]

Bill

 

I think when implemented as strings rather than self supporting stiff vanes the strings are done in pairs.  This means for a 3 "vane" spider there are actually 6 strings.  Each pair comes to a vertex at the wall of the OTA and is spaced out when attached to the hub to form an isosceles triangle.  A vertex angle of something like 30 degrees is probably desireable to minimize vibrations.

 

jtm

 

----- Original Message -----

From: William Kelley

To: atm@shore.net

Sent: Sunday, October 21, 2001 8:12 PM

Subject: ATM Re: string spiders

Hi Friends,

 

I was giving thought, and concern, to string spiders not providing very good axial support,

no matter how tight the strings. With 3, the optimum and minimum, the secondary can still

vibrate along the optical axis. Or have I misunderstood something about how they might

be used?

 

If this is a problem, it occurred to me that the shadow cone from the center of the secondary,

to the center of the primary, might offer a pathway for installing one more vertical string that

would act as a guy at right angles to the secondary assembly. and with very little tension

eliminate all vibration. Being in the shadow of the secondary it coudn't add any more diffraction

error.

 

Thinking about stuff like this makes my head ache, so after superficial consideration, please delete

without spamming me.

 

Regards to all,

 

Bill Kelley