Big Bertha Behaves

It turned out the decline in performance was a collimation problem--and a reminder that you shouldn't ever trust appearances. The focuser is an older University Optics 2" inside diameter focuser. Instead of a 1.25" adapter that slides inside, instead, you unscrew the 2" collar, and screw the 1.25" adapter in its place. It is a little clumsy, and the 1.25" adapter collar looks cheap.

So I pulled out a more common 1.25" adapter from a 2" diagonal that I had lying around. (It came with my 5" refractor.) This adapter looked and felt like a finely machine piece of work--so I put that into the 2" focuser a couple of nights ago. It did not even occur to me that the decline in image quality might be connected to this finely machined adapter.

When you turn the focuser in with the laser collimator in the focuser, if everything is in the proper position, the laser beam will hit the same spot on the primary mirror. With the cheap 1.25" screw on collar, that pretty much happens. With the finely machined (or so it seemed) adapter, the beam moved a half inch across the mirror as I turned the focuser knobs. It turns out that the finely machine focuser from somewhere in China is actually pretty sloppy in its tolerances.

Anyway, last night, I went to the crummy looking but well-made Japanese adapter, and once the mirror had cooled down--with a little help from a muffin fan--I can honestly say that the telescope is now behaving at about the level that I would expect from a Coulter mirror. It is a little disappointing, compared to my 8" f/7 reflector, which uses a Coulter mirror from the 1960s, when they advertised mirrors accurate +-1/25th wave (and I think managed to do it), but for a telescope that cost me this little, it does okay.

At 500x on the Moon, the image isn't tack sharp, but it isn't all that bad. At 222x on Saturn, Cassini's Division is visible all the way around the planet, although it isn't terribly dark. The brown cloud band on the planet is clearly visible. There is a little bit of either coma or undercorrection--not sure which--that keeps me from going much higher on Saturn--although I think there is more detail visible at 222x with this beast than I can see on my smaller telescopes, even at higher magnification. (Remember that even at the same magnification, a larger aperture telescope will reveal more detail. Dawes' Limit says that resolution is directly proportional to aperture diameter.) I will have to roll the 5" refractor out tonight to do a direct comparison.

Where this telescope does well--and the primary reason that I bought it--is for deep sky objects. I don't have a dark enough sky here to make much use of it yet, but on the Orion Nebula (M42) using 80x--oh wow! The detail that it brings out, and the subtle colors as well--just amazing. I look forward to moving this beast to my Horseshoe Bend property in a few months, once we get construction under way.