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Can you buy adjustable spiders?

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#1 25585

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Posted 11 June 2021 - 07:05 AM

I am not looking for a fit-any-size aperture, but just enough adjustability to cover same-aperture OTAs with slightly different inner diameters, for tube changes.



#2 Dick Jacobson

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Posted 11 June 2021 - 07:40 AM

I have adjusted Astro Systems spiders to slightly different tube diameters, simply by using longer screws at the ends of the vanes. In theory, this could cause a tiny amount of diffraction if the end nuts intrude into the field of view, but I don't think this is significant.


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#3 Jon Isaacs

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Posted 11 June 2021 - 08:45 AM

I have adjusted Astro Systems spiders to slightly different tube diameters, simply by using longer screws at the ends of the vanes. In theory, this could cause a tiny amount of diffraction if the end nuts intrude into the field of view, but I don't think this is significant.

:waytogo:

 

And you could use a slightly long spider, drill and oversized hole and the use stacked washers that fit around the coupling nut?

 

Jon


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#4 DouglasPaul

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Posted 11 June 2021 - 08:58 AM

What size? Maybe something like this would work?

 

https://www.ebay.com...HoAAOSw8elgwDG9


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#5 Jon Isaacs

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Posted 11 June 2021 - 09:17 AM

What size? Maybe something like this would work?

 

https://www.ebay.com...HoAAOSw8elgwDG9

 

Scopes are sometimes made with rods.

 

The rods are necessarily large in diameter and cause too much diffraction.  Dick's solution is much better because the rods do not extend into the high power field where spider diffraction is a concern.

 

Jon


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#6 Tonimus

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Posted 11 June 2021 - 11:21 AM

+2 to what Dick said. Get the spider for your smallest tube and a selection of longer screws. 


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#7 25585

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Posted 12 June 2021 - 08:42 AM

I'll try that! waytogo.gif




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