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ota and dovetail

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#1 gonzosc1

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Posted 01 December 2012 - 08:27 AM

waiting for my new Atlas to get here. just received a used C9.25 and it has the small dovetail on it but to me it does not feel study enough. it needs to be tighten up, as I look at it I see there are only 2 very small screws that hold them together.
I'm new to EQ mounts so I don't know, should this rail be upgraded to something bigger? if so what do I need?

#2 mclewis1

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Posted 01 December 2012 - 11:18 AM

The Atlas uses a Vixen/CG-5 dovetail size saddle, the CGEM and new Skywatcher EQ6 use the wider Losmandy D style saddle (I believe the EQ6 uses a saddle that's actually compatible between both these types of dovetail bar/plates).

The Vixen/CG-5 is 1.75" wide but quite thick. The Losmandy D type is wider at 4" but usually thinner. The Losmandy D is stiffer than the Vixen/CG-5 and more suitable for larger otas. The C925 is around the point where the trade off starts to make some sense (length of bar and weight of the ota both come into play).

I prefer the more robust D type plate but there are many folks who use a C925 (and even a C11) with the smaller dovetail bar quite successfully.

With an Atlas you also have the option of upgrading the saddle to the ADM dual saddle which can handle both types of bars/plates (there are also other choices). I personally think this would be a good direction, especially if you are planning to do some imaging in the future. The ADM dual saddle for the Atlas, ADM Losmandy D type plate for the 925 and the appropriate radius blocks (used to securely attach the plate to the ota).

#3 gonzosc1

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Posted 01 December 2012 - 11:26 AM

ok thanks. I'll stay with whats on it now as I'm just visual for now. if I get into AP I will upgrade to the D type.


The Atlas uses a Vixen/CG-5 dovetail size saddle, the CGEM and new Skywatcher EQ6 use the wider Losmandy D style saddle (I believe the EQ6 uses a saddle that's actually compatible between both these types of dovetail bar/plates).

The Vixen/CG-5 is 1.75" wide but quite thick. The Losmandy D type is wider at 4" but usually thinner. The Losmandy D is stiffer than the Vixen/CG-5 and more suitable for larger otas. The C925 is around the point where the trade off starts to make some sense (length of bar and weight of the ota both come into play).

I prefer the more robust D type plate but there are many folks who use a C925 (and even a C11) with the smaller dovetail bar quite successfully.

With an Atlas you also have the option of upgrading the saddle to the ADM dual saddle which can handle both types of bars/plates (there are also other choices). I personally thingk this would be a good direction, especially if you are planning to some imaging in the future. The ADM dual saddle for the Atlas, ADM Losmandy D type plate for the 925 and the appropriate radius blocks (used to securely attach the plate to the ota).



#4 Geo.

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Posted 02 December 2012 - 03:32 PM

You can pick up the CGEM bar for the 9.25 on eBay for under $40.

#5 Dan Watt

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Posted 03 December 2012 - 12:35 AM

The new Atlas mounts actually ship with a dual saddle, one that accepts both vixen and losmandy plates so I would go ahead and get the beefier plate

#6 gonzosc1

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Posted 03 December 2012 - 05:48 PM

Question on the plate install. is this just a bolt on project or do I have to go inside the tube to get to nuts and bolts????

#7 mclewis1

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Posted 03 December 2012 - 07:18 PM

Just a bolt on project. For the wider D type plate installation you first install the radius blocks by removing existing bolt pairs and replacing them with the hardware that comes with the radius blocks, and then the plate bolts to those radius blocks.

It's important to use the correct length hardware for anything that gets attached to the ota, at the rear cell you have to be careful of bolts that are too long protruding too far and interfering with the movement of the primary mirror.

The bolts you see that have thin nuts on the inside of the ota are not intended to be ever removed, they hold the front or rear cells to the tube.

#8 gonzosc1

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Posted 03 December 2012 - 08:23 PM

OK great, thanks






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