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yet more secondary questions

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#1 bunyon

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Posted 18 June 2013 - 12:46 PM

Make that questions about secondaries. If I wished to buy a larger secondary, can I only buy a new holder or must I buy a new spider as well?

The only suppliers I'm aware of are Antares and Protostar. Does that about cover it?

Thanks.

#2 robininni

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Posted 18 June 2013 - 01:07 PM

You do not necessarily have to buy a new spider.

I purchased a 4.5" secondary to replace the 4" secondary I had. I bought an Astrosystems holder for the new secondary and made sure that the existing secondary holder (which either was an Astrosystems holder, or was very similar to theirs) and the new one both utilized the same diameter mounting bolt that slips into the spider.

The only problem I ran up against was that with my UTA and the spider mounted in it, I cannot move the new 4.5" mirror far enough away from the primary to square the focuser. I could remount the spider with, what I consider, a severe amount of effort, but I have instead decided to just move the secondary away as far as possible sans remounting the spider. (I did have to drill new holes in my Astrosystems holder to help facilitate this or else it would have been so far off center it would not have worked well I don't believe)

I hope this helps.

Rob

#3 DavidC

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Posted 18 June 2013 - 01:14 PM

AstroSystems makes secondary holders with a threaded center rod or bolt. They also make spider vanes, but I've heard there is a wait. If you have a spider vane that works with a 1/4 or 3/8 inch threaded center rod, you can just get a new holder for the secondary.
David

#4 Achernar

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Posted 18 June 2013 - 01:32 PM

Usually the spider and secondary mirror holder are separate components. Sometimes the spider and secondary mirror holder are integrated together, like the Protostar spider I have in my 6-inch Dob. The adjustment mechanism for the secondary mirror tilt is in the hub, not the holder. Tradistional spiders and holders place the adjustment mechanism in the holder itself. If this describes what is in your telescope, just order a new secondary mirror holder to match the new secondary mirror you plan to install.

Both can be ordered from Astro Systems, whose website can be accessed at the link below.

http://www.astrosystems.biz/

Taras

#5 Mirzam

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Posted 18 June 2013 - 01:59 PM

I recently ordered two Astrosystems spiders + secondary holders; they are manufactured to order and required about a month to finally arrive. Protostar wait times are pretty much indeterminate (i.e. very long).

The shrouds used in the Astrosystems holders eat up a fair amount of area around the edge of the secondary. In one of mine I ended up scrapping the shroud and using a glued wooden dowel to support the secondary. This only becomes an issue if your secondary is near the minimum size for the OTA configuration.

JimC

#6 DavidC

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Posted 18 June 2013 - 03:13 PM

On my secondary holder for my 13 inch, there is not even an 1/8 inch overlap on the edge of the mirror, I don't think that really matters, unless you have a smaller mirror. Plus I really love the 4 thumbscrew push - pull alignment method of adjustment.
David

#7 bunyon

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Posted 20 June 2013 - 07:45 AM

The pictures on the Astrosystems site certainly look like the ones in my scope - a Classic Obsession. Looks like I can get what I need there. Thanks all.

#8 Pinbout

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Posted 20 June 2013 - 08:19 AM

know what size scope and secondary would help clarify somethings.

you could get a stalk from 1800destiny, you'll have to glue it to the back of the mirror cause they don't make them with the typical shrouds.

#9 Asbytec

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Posted 20 June 2013 - 08:26 AM

What about the weight of the larger secondary? Will it stress the spider or create some sagging as the scope is slewed around the sky? Does that matter?

#10 Pinbout

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Posted 20 June 2013 - 08:36 AM

it can, and that is one of protostars complaints about gso spiders. you have all this alum. holding a secondary, and the length of their alum stalks can create a momentum to twist the spider.

#11 bunyon

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Posted 20 June 2013 - 08:59 AM

Classic Obsession 15. Came with a 2.6" secondary. I, somewhat foolishly, cut my poles down to get a camera to focus and cut too much. At this point, I have zero fully illuminated field and a good bit of drop off at the edges. I can go with longer poles but am also considering a bigger secondary for all the reasons one normally hears about that being good.

It will take me from 17.3% CO to 20.6%. Not significant, IMO. The existing secondary is almost 10 years old, so a new one might bring other benefits as well.

Still mulling.


Ideally, yes, I'd go with the protostar integrated system. However, it will take longer (wait times), cost more (more than double) and involve surgery on the UTA. If the existing spider can't take the 3.1, I can just go back to the 2.6 with longer poles or buy the protostar at that point.

Mostly, I was just wondering who sold these items and the astrosystem secondary holder looks to be an exact match for the spider I currently own.

#12 bunyon

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Posted 20 June 2013 - 09:00 AM

Also, FWIW, the 3.1 will have to be racked right up tight to the spider by my measurements (not tight, but close to it). There won't be much of a moment arm. Less than with the 2.6 to be sure.






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