Has anyone done this? Because at my latitude, the windows of imaging opportunity are always small, so I am interested in simultaneous imaging of [say] Venus in UV and IR. I cannot find clear information on the load capacity of a 14 inch LX200GPS mount, but I suspect that if if thus loaded it would still just about handle it. Any experience?
PIGGY-BACK 8 INCH LX200 OTA ONTO A 14 INCH LX200 GPS
Posted 13 July 2021 - 04:40 PM
Is this on the fork and are you using a wedge? To balance the load in that case you would need as much weight mounted on the bottom of the 14" OTA to equal the 8" on the other side. With a GEM you can use the CWs on the DEC shaft to off set the weight of the 8". At low angles its not a lot of trouble but near the zenith the 8" will create a lot of imbalance and put pressure on the locks and gears. That is why they made those sliding weights that fit on a dovetail mounted on the bottom of the tube on a fork mount.
Posted 13 July 2021 - 04:53 PM
I found this on the web a while ago and if memory serves: My 8" can carry something like 20lbs. extra on it as far as load capacity of the forks and gears. The 16" at the observatory can handle around 60lbs.
So you should be good with an 8" scope on top. I think I agree with photoracer18 about balancing the weight top to bottom if you are going near zenith. The counter-balance weights on the bottom are normally only to balance the scope front to back when it's horizontal so they may not be enough to off-set something that large on top. And, if you have it on a wedge you should make sure the wedge can handle the extra weight and stress from the off-set load on top of the scope.
Posted 13 July 2021 - 05:16 PM
I have piggybacked my 8" Celestron SCT on my 12 " Meade LX 200 without issues. Always a struggle to balance an SCT fork mount accurately which is critical. I have since deforked and gone with a GEM - much easier to balance although that design has quirks too..
Posted 14 July 2021 - 01:01 PM
Yeah, you might be hitting the limits of your rig with the configuration you are suggesting.
I do dual imaging, 80mm ED APO or 70mm Quad Astrograph with my 14" f/8 ACF. BUT...I do this with an LX850 GEM mount which works perfectly with this configuration.
Consider the load: the 14" and 8" OTA, guiding equipment, cameras, filters...it may be too much for the LX200. I am running around 85 lbs for my LX850 GEM.
Posted 14 July 2021 - 04:56 PM
Thanks for all this input. In the piggyback arrangement I would only ever be shooting planets and I do not envisage ever getting to the Zenith. For deep-sky [and comets] I would always use a different configuration. So it looks like it might be possible, though marginal
Posted 14 July 2021 - 05:03 PM
The capacity of the 14" LX200 should hold the 8". Depending on how you plan to mount it and gear used with it expect your weight to be 16-18lbs.
I would suggest contacting Peterson Engineering and getting both the EZ Clutch kit and the Buck's Gears to help with the extra stress you'll be applying even after proper balancing.
Due to the counterweight you'll need to use on the bottom I'd look at the ScopeStuff Balancing kit. http://www.scopestuff.com/ss_baln1.htm
You should be able to make your own weight stock for this kit as it uses 1/4-20 threading and you can place weights where you need them.
I use this kit for my LX200 10" and love it. Though I'm currently only blancing a binoviewer, I'll be mounting an 80mm on top in the future.