26 replies to this topic

[deSitter]

"There is some astigmatism. The defocused star is slightly oval close to focus). It is not enough to turn the stars into "plus signs" in focus. In focus, it produces an airy disc with a bright, core with dim diffraction rings. I figure that any scope can do that can deliver a bright airy disc, it is more limited by diffraction than anything else. The diffraction rings are stronger on one side, like slight coma."

 

This is characteristic of miscollimation. My SkyChief's main problem is the mating of the cell to the tube, which is so loose it can be pulled off. I had to bulk up the threads with blue tape.

 

-drl

[ericb760]

I have tested the old sky chief a bit more.

STAR TEST

I used an artificial star and did a star test. It is brighter than most real stars, and brings out more fuzz. My star testing is basic. I can't tell 1/6 wave from 1/7. I have three categories:

1. There's something seriously wrong here...
2. Decent. Don't worry. Enjoy the views.
3. Fantastic! Be happy!

Keep in mind that a star test is VERY sensitive. There is some signs of spherical aberration. The defocused star is a bit more fuzzy on one side of focus than the other. There is some astigmatism. The defocused star is slightly oval close to focus). It is not enough to turn the stars into "plus signs" in focus. In focus, it produces an airy disc with a bright, core with dim diffraction rings. I figure that any scope can do that can deliver a bright airy disc, it is more limited by diffraction than anything else. The diffraction rings are stronger on one side, like slight coma. Something you don't expect to see in a refractor. I guess the lens is a bit decentered because i opened it. It is something I will try to correc.

All in all, the verdict is "decent". I have seen worse, but also better. Maybe even a decent+ if I can center the optics better.


UNDER THE STARS

I took a quick look at Jupiter last night through a hole in the clouds.
The moons look pinpoint. The cloud bands are readily visible. The FOV of the original eyepieces is really narrow. I know there is false color in achromats, but I didn't really notice much.

The most annoying defec is reflections due to scratches inside the diagonal.

The mount is bad. It's very light, which is in itself a good thing. I think the wooden tripod is a bit better than light camera tripod. The alt-az head The most annoying thing is that it is front heavy, and that the thumb screws that fixes it in Alt becomes loose when the scope is moved. Not a good design.


The focuser is pretty ok. Tight at sturdy.

CONCLUSION
I remember everyone was knocking ok these scopes 20 years ago. There were comments like "Is that a Bushnell, or did someone cr@p on my tripod?". It was a bit off putting, and I was convinced that the scope was useless. I don't think it's a Takahashi by any means, but it's decent. Little CA. Fairly sharp. Mostly glass, steel and wood. It's a real telescope with real optics, and certainly way better than the modern cheap frac that Ed Ting recently reviewed.

WHAT DOES THE FUTURE HOLD.
It has spent 35 years in the attic. I want to bring it to life again. I have bought a Vixen bar and a 0.96" - 1.25" adapter, and I will do some imaging one day. Jupiter maybe. :-)

I have a Bushnell Sky Chief Jr. I believe it to be 60/700. I, too, tried an 0.965" to 1.25" adapter but it would not come to focus with it. I ended up buying a 0.965" to 1.25" hybrid diagonal from Scopestuff and it does work. Mine has amazingly crisp views of the moon and planets. I was lucky enough to have a set of rare 60mm rings that I use to attach it to either an AZ3 mount or my C4.5's Polaris.