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Another mirror cell thread

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#1 Piero DP

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Posted 09 October 2019 - 03:26 PM

I looked at the images of a few 9-point mirror cells on the Internet and noticed that the triangles are only attached with a bolt. Does this mean that they can also rotate, apart from the normal vertical movement? If this is the case, isn't there a chance that the rotation of the primary mirror can cause an unwanted rotation of one or more triangles, determining unequal mirror support? 

 

Secondly, at page 186 Sidgwick says that "insufficient central support, allowing the axial region of the mirror to sag, will cause spherical over-correction" (pg 186, section 10, Amateur Astronomer's Handbook).

Can unwanted rotation of triangles cause spherical over-correction?

 

Thanks for your help



#2 havasman

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Posted 09 October 2019 - 04:15 PM

Many modern mirror cells have attachments from a support triangle to its neighbors. My Starmaster uses thin braided cable, New Moon uses springs. They keep the system in place and prevent rotation of the triangles.


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#3 brebisson

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Posted 10 October 2019 - 12:16 AM

Hello,

 

Normally the triangles are held one way or another to avoid turning...

 

However, I would discourage you from going 9 points...

If you run the number through plop, you should discover that the 9 point cell give little to no improvements over the 6 point cell, while being much harder to make and much more prone to slight variations compared with the optimal...

 

Cyrille



#4 Pinbout

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Posted 10 October 2019 - 05:53 AM

If 6 was 9 - hendrix

 

guess he never made a telescope cell.

 

if 9 was 6 you’ll be happier 

 

or go 18 if 6 isn’t enough.

 

https://youtu.be/ifSMbmCxf1I


Edited by Pinbout, 10 October 2019 - 05:54 AM.


#5 Pinbout

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Posted 10 October 2019 - 05:58 AM

Most use a kydex ring to keep triangles in place

 

https://youtu.be/wBk66Mm0eC4



#6 Piero DP

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Posted 10 October 2019 - 11:18 AM

Thanks for your replies.

#7 Arjan

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Posted 10 October 2019 - 02:50 PM

If 6 was 9 - hendrix

 

guess he never made a telescope cell.

"Now if 6 turned out to be 9
I don't mind, I don't mind
Alright, if all the hippies cut off all their hair
I don't care, I don't care
Dig, 'cos I got my own world to live through
And I ain't gonna copy you"

 

 

Makes for a better text though.

Where's the time?


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#8 Arjan

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Posted 10 October 2019 - 02:51 PM

Most use a kydex ring to keep triangles in place

Why kydex?



#9 Pinbout

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Posted 10 October 2019 - 05:48 PM

Cause they have left over from their baffle on the uta tongue2.gif


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