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AT12 RC install (I apologize in advance for the incoming clouds)

Interesting day yesterday. I had taken delivery of the AT 12 RC telescope a few weeks ago. It had been sitting in my living room floor, until yesterday when I finally got the time to install it. My trusty VC200L was unmounted, after 4 years of great service at Asteria observatory, with the peak being last year where I accumulated a rather large image backlog due to the nice weather from spring to fall. In total, I have owned that scope for 10 years. But I digress. Back to the AT 12.

Mounting and balance

Unpacking it I thought this this is huge and awkward to pick up or maneuver. Coming in at 49lbs., is a beast compared to my 8''. My dear daughter Rosie is a tennis athlete so she helped me carry and mount it (took a few tries). My mount is an Astrophysics 900 GTO, with a weight capacity of 75lbs. and has been tested up to 90lbs., so the 12'' is well within its weight limits. For those interested in the technical details, here is a photo walk through of the install.

Once I removed the AP 12" Vixen Dovetail Converter (SBD2V) holding the VC200L, I noticed that the 16" Easy-Balance Dovetail Saddle Plate (DOVELM162) had only 2 bolts holding it down. I was able to get 4 in there for the extra stability.

I then mounted the two Astrotech dovetails side by side. It is highly recommended to have two, which span 2ft 3'' from end-to-end, due to the length of the scope.

Then the rings got mounted, I didn't go the full length of the bar, as I don't like the ring being near the edge in the front. Instead, I put one in the back, and one towards the middle.

Second order of business were the counterweights. With the shaft pointing down, per AP, I put the two 24lb. counterweights up at the very top, so there is more stability.

Things got interesting after that. Upon mounting the scope in the open rings, there was an immediate shift in the RA axis, even though the clutches were tight. That's from being out of balance, we had to hold it from sliding down until adjustments were made. Yes, the scope is THAT heavy. Once balanced in RA, it became more manageable. Sadly, no matter what combinations of weights I tried, I couldn't keep the two 24 pounders at the very top. The 18lb. at the bottom was also necessary after I added the camera gear. Balancing DEC was time consuming and hard. Had to bring the scope at the upright position, loosen the clutches while holding it tight in the back, nudge it forward or back, tighten clutches, test in the park position, rinse and repeat. Took about 5-6 iterations to get it close to right. Still not perfect, but it will have to do for now :)

Rough collimation

I thought the scope was in pretty good collimation judging from the laser collimator I used. I made the mistake trying to tweak the secondary, and messed up the alignment quite a bit, although when I fixed it I thought it looked better than before. I left primary mirror alignment for the stars later.

The focuser on this scope is very beefy. It can easily hold my 10+lb. worth of camera gear. No sagging, slipping or anything of the sort. In fact, the camera gear looks petite compared to the focuser, even counting the OAG and guider setup.


It's getting late in the evening, and I am behind. The observatory still looks like a construction zone, tools, trash, parts scattered everywhere. And then there is the cabling. This is an area I dread every time. The biggest problem is that certain power adapters like the filter wheel, don't have enough slack to go up the pier and over to the scope. This scope is LONG, I don't thing I've stressed it enough. I had to undo a few zip ties at the top of the pier to give it slack. Tested by pointing the scope manually south, and it's a stretch. Still not happy with this, but it is a work in progress. It is particularly important when it's a remote unattended setup (use your imagination for the rest). I had to tie camera gear on the camera's fan, since that was the only place I could, so the cabling doesn't way down the setup and become loose.


Another setback was that the focuser shaft on this scope is different that any of my previous ones, so I have to order an adapter for this next week, so stay tuned on this one.

Camera configuration

I had got the AP 0.67x telecompressor to widen the field. Prime focus imaging with this scope is at f/8, at a focal length of 2,432mm. With my camera, this gives a 0.46 asp pixel scale. The reducer would take it to 0.68 asp which is more manageable, with a wider field. However, I quickly discovered that I did not have the correct adapter to couple it with. I need to talk to AP to see what we can figure out. As it stands, I have the exact same setup I did with the VC200L, imaging at f/8.

The autoguider was a breeze to refocus, as it was only slightly out of focus to begin with.

Fine collimation

I use CCD Inspector for fine collimation. That is what turned my previous scope around as well. Defocused star collimation works best. As I suspected, it was off at first by some 16 arc seconds, but managed to bring it in to around 1''. I will see how that holds up, and go from there. Being unfamiliar with the pull/push screws of different sizes, I couldn't figure out in the dark that I was using the wrong allen wrench for the push screws the whole time :(

Final thoughts

By the time I was done with everything, it was past 2:30a.m. I was ready to call it a night, but the Milkyway overhead and the thousands of stars mixed with a layer of thin clouds were calling my name. So I pointed the scope to a random target on the map which happened to be Stephan's Quintet in Pegasus This is 90 minutes, 600sec luminance subs, manual focus, imaged through thin cloud layer. I was blown away by the level of detail and scale compared to the 8''. Also the stars are tack sharp, given the oversampling at 0.46''and the scope gives a completely flat field. No flats needed. You can clearly separate all the galaxies in the Quintet.

I have very high hopes for this setup, it should be interesting to say the least. As for the reducer I mentioned above? Never mind, I think I will leave it as is.

(Iphone's attempt at low-light image = fail)


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