Re: Refractor on top of OTA ok? AP 1100 GTO Mount

David Enck

Thanks for the advice, you temp me for a larger refractor :-). Although the C14 is a good bit lighter than my lx850 Meade 14..

On Dec 2, 2020, at 1:29 PM, Christopher Erickson <christopher.k.erickson@...> wrote:

I would put a tandem bar on top of the mount and the two scopes side by side. I have done that with a C14 and a 130EDF-GT with good results.

ADM has tandem bars.

Don't be tempted to put a guider on the refractor. Way too much flexure in the reflector for that to ever work. Use an off-axis or on-axis guider on the reflector instead.

There will be some inevitable pointing error between the scopes. You can either:

1. Don't worry about it. There will be inevitable differential flexure as you move around the sky. 

2. Use adjustable rings on the refractor.

3. Use an ADM X-Y adjustable platform under the refractor.

-Christopher Erickson
Observatory engineer
Waikoloa, HI 96738

On Wed, Dec 2, 2020, 10:52 AM George <george@...> wrote:



I do not recommend it due to the enormous moment arm.   Sticking the 20 lb. refractor on top, way out from the center of gravity is like adding 40-50 lb.






George Whitney

Astro-Physics, Inc.

Phone:  815-222-6538 (direct line)

Phone:  815-282-1513 (office)

Email:  george@...


From: <> On Behalf Of David Enck
Sent: Wednesday, December 2, 2020 2:28 PM
Subject: [ap-gto] Refractor on top of OTA ok? AP 1100 GTO Mount


Hello AP Folks,

I  currently run a Meade LX850 14 inch SCT  ota on my 1100 GTO. It handles it beautifully for visual and photography.. I am  looking to possibly add a Takahashi TSA 120  APO to the mix. My 14 inch weights about 75 pounds with all the gear on it. The new TAK 120 is 15 pounds bare, so about 20 with rings and a dovetail bar..  If I  choose to mount it on top of the OTA will it be ok? I  have about 118 lbs of counterweights available to me to use to counter balance it.

I am looking  to  go this route vs side by side  mounting as it will be more difficult to  balance the dec axis by myself with this much weight involved trying to slide the saddle plates back and forth. There is a  huge weight difference between the two scopes..

Thank you for you  advice and thoughts!  


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