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Tuesday, May 14th, 2013
Focuser Upgrade
 
The stock focuser on my AT111EDT looks very impressive.  It's large and heavy, has a rotator, and very smooth rack & pinion focus mechanism.  It was one of the reasons I bought this scope.  But once I started using it I grew less and less impressed with it, although I am still very happy with the optics.  The first problem was that the rotator wobbles even when tightened as much as I could do by hand.  I discovered that this was due to a design defect and I was able to fix it and was satisfied with it for quite a while.
 
However, last year I discovered that I had a problem with differential flexure and could not get rid of it.  I ended up going to off-axis guiding and, despite some awkwardness involved in OAG, that solved the problem.  Later, I realized that the problem was probably due to the focuser.  I had decided earlier that it needed to be locked down to be solid, but now I find that even when locked down it is prone to a small amount of flexure in certain directions (which is why I didn't notice it until I tried to image M16).
 
Another problem with locking the focuser is that it prevents me from using the temperature compensation feature of my PerfectStar Focus Controller.
 
So I made the adapter shown below to put a FeatherTouch 2.5 inch focuser on the AT111EDT.  It was fabricated from aluminum tube with 4.5" OD and 0.5" wall thickness.  Each end is turned to match the diameter of the mating piece.  The inside (other than the threaded areas) is left at 3.5", but is grooved and painted black to avoid reflections.
 
It hasn't seen "first light" yet, but I'm pretty pleased with it.  The sad thing is that I recently purchased a small lathe/milling machine, but this project was too big for it and I had to use my friend's shop.  My small machine will be more than adequate for my business needs, but personal projects like this can be another story.
 


Image Gallery For This Session
FTadapter FTonAT111
   

FTadapter.jpg
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