Upgrade M50

The ETX-125 tube assembly is about 8-9 pounds. it's compact enough so that it's quite stable on the SGP mount. It's way more stable than it is on the Meade's fork mount, that's for darn sure! It was a calm night and once I stopped touching the scope it didn't move or vibrate at all.

The only 'motion' I saw through the scope and in exposures was very slight tracking drift. With the drive on I would easily shoot frames to stack for 20 minutes with no need to re-position the scope.

Turns out the model I bought off Craig's list was the original ETX-125EC from 20 years ago, not the observer model with GOTO. So I don't feel so bad only using the optical tube assembly -- the optics are still very clean and sharp.

Here's a photo of the M6ii mounted on the scope with the SGP on a strong Bogen Manfrotto tripod , using the Meade photo adapter, canon T-ring, and Canon EF - EOSM adapter. I have 2 counterweights which balances the OTA/camera nicely (only one counterweight is shown).

The ETX-125 not a deep-sky scope, its f-ratio at f15 is too dark, it's really a Moon and planets scope. You really want about an f6 scope (or an f10 scope with a focal reducer) to do DSO work.

Nevertheless, I couldn't resist trying to shoot the Orion Nebula through the scope with the M6ii to see if it was possible.... It's probably the only 'bright' DSO you can shoot with this config. This was more an exercise to see how the mount would track etc.

So I shot 80 15-second images at prime focus (f15) using the M6ii at ISO 6400 with fairly good polar alignment and the tracking drive on. Of those 28 frames were 'sharp enough' with nearly point stars to stack using DeepSkyStacker. In the unusable exposures, the star images were elongated -- about 1.5 - 2x as long as they were wide. For 1900mm this is not a bad performance!

There was enough grain and noise in the ISO 6400 images, that I decided to process them all using DxO PL5 first (saving to large TIF files), applying Deep Prime to smooth the noise out a bit, applying CA and sharpening a bit. Stacking those TIFs brought out more detail in the nebula, and also brought out much fainter regions near the edges of the frame.

As the scope was magnifying more than the 'seeing limit' the image isn't pixel-sharp the way a short exposure of the Moon or a planet might be in good seeing conditions. But the result has more fine nebular detail than a 135mm or 200mm telephoto shot would have.

Single exposure, processed in DxO:

Canon M6ii, Meade ETX-125 scope at prime focus on iOptron Sky Guider Pro, Single exposure of 15s at f15, ISO 6400, processed using DxO PL5

28 Stacked exposures:

Canon M6ii, Meade ETX-125 scope at prime focus on iOptron Sky Guider Pro, 28 x 15s (7 min total) at f15, ISO 6400, Each frame process to TIF using DxO PL5, images then stacked using DeepSkyStacker. final result processed again in DxO PL5

For comparison, here's a shot of stacked images the same night with the M6ii and the Rokinon 135mm f2 lens. The flame nebula is also visible upper right, and to the left of that, the Horsehead nebula is barely visible:

Canon M6ii, Rokinon 135mm f2 lens, 40 x 30s (20 min total) at f2, ISO 100, Stacked using DeepSkyStacker with 20 each dark, bias, flat, and dark/flat frames

Excellent results!  Thanks for the insights, and for the info on the OTA weight.  9 pounds is too heavy for my mount.  I'm right at the 11 pound limit on my Star Adventurer using a Tamron 150-600 zoom that weighs only about 4 pounds.