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Focuser question

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#1 flygal6

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Posted 07 May 2013 - 10:50 PM

I have a 6" reflecting Newtonian telescope my father and I built from scratch when I was a kid. I am looking now to make some updates to it now. I have seen some crayford type focusers listed here, 1.25" and with curved base. How much does the tube/mirror size (6" vs 13") affect the fit of the focuser to the tube? In other words, can a focuser used on a larger scope, still fit and work on a 6" one? Just want to make sure there isn't something I am missing and don't want to waste my money with something not compatible.
Thanks Carol

#2 CosmoSat

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Posted 08 May 2013 - 12:32 AM

Hi Carol,

The bases are available in sizes that fit the tubes curve.

GSO Crayford Focuser for Reflectors - Single Speed

GSO Crayford Focuser for Reflectors - Dual Speed

Choose the one u want from the selection menu.

The single speed focuser should work well with a f/8 scope.


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#3 Jon Isaacs

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Posted 08 May 2013 - 05:17 AM

I have a 6" reflecting Newtonian telescope my father and I built from scratch when I was a kid. I am looking now to make some updates to it now. I have seen some crayford type focusers listed here, 1.25" and with curved base. How much does the tube/mirror size (6" vs 13") affect the fit of the focuser to the tube? In other words, can a focuser used on a larger scope, still fit and work on a 6" one? Just want to make sure there isn't something I am missing and don't want to waste my money with something not compatible.
Thanks Carol


Carol:

You do need to make sure the focuser base fits the tube, that can be a problem with a smaller scope. If the tube is robust, a focuser made to fit a larger tube can be used by using washers between the focuser and the tube but it's better to have a focuser that fits.

Also, you need to make sure the focuser height, that is the racked in focuser height as well as the travel will allow the scope to come to focus.

Jon

#4 Achernar

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Posted 08 May 2013 - 07:44 AM

Many focusers have a universal base that fits all round tube sizes, or you order it with base suited for a particular size tube. It is worth the money to buy a good focuser, when I built my 15-inch I spend $265.00 on a Moonlite focuser for it, and I never regretted it because smooth, exact focusing at high power is a pleasure. I had to order it with a flat base because of how I had to mount it however. Premium focuser makers also offer everything you'll need to fit their focusers to any sort of tube. You can certainly get a good one for much less than that.

Taras

#5 Geo.

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Posted 08 May 2013 - 08:58 AM

Or mark the tube on the side exactly opposite the center of the focuser. I usually drill a small hole there. Apply some Bondo body filler to the area where the focuser will sit. Fit the focuser, get out your site tube and align it, clean up any squeezed out filler and let it cure.






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