Greets--
Cloudy all day today, so I spent the afternoon replacing the focuser on
my recently acquired MN-66 Mak-Newt (6", f/6). I had an old JMI crayford
unit laying around in the shop, and although it had a slightly curved
base, and the curve didn't match the MN-66 tube, I installed it in place
of the original focuser. Simply loosened the tiny (1.5mm?) screws on the
base plate and the guts of the focuser fell off in my hand.
The focuser is the big weak point on these scopes. They are cobbled
together crayford-style units with a fit so poor and wobbly that they have
a nasty habit of falling apart under the force of gravity, often with a
big EP in them, when you're rotating the tube. Ugly. Sounds like breaking
glass hitting the patio.
Using the original base plate, I centered the drawtube and marked it
for 4 8-32 holes. A #29 bit, a Milwaukee variable drill and bingo, it was
a done deal. Tap the holes, stick the new unit on with some allen-head ss
cap screws and I'm ready to collimate.
Since I bought the scope second hand, I found the secondary loose
enough that it would spin on the meniscus glass when I tried to adjust the
secondary collimation screws. Ended up removing the meniscus glass
(corrector plate to you SCT folks), aligning the secondary with a laser
and using s drop of blue loctite to secure the brass thumb nut that holds
it all in place on the meniscus glass. I took an hour and a half to
collimate this little scope. Hard to believe, but I wanted to get it
right, so I ended up going back and forth, ultimately adjusting the
focuser position to center it over the secondary. The original baseplate
has two slots for the attachment screws that make this a trivial matter.
The offset is already built in to the secondary holder (nice touch).
Aside from the original focuser, this little scope is built like a tank,
so once you collimate, it stays put for a long time.
After dinner, there was a break in the clouds and Lyra was visible, so I
quickly set up and opened the scope's vents to let it cool down. 15
minutes later, I was doing a star test on Vega. Even though it had been
cloudy, there were nice, steady diffraction rings around a slightly
defocused star image at 130x (7mm nagler). The star image inside and
outside of focus was as symmetrical as those in my old FS-102 Takahashi,
but a hell of a lot brighter. The field at 30X was free of coma to the
edge (35mm Panoptic). I was able to split the double-double cleanly. It
looked like you could put a feeler guage between the two doubles.
I have heard people say that these scopes deliver refractor-like
images, and I can attest to this example's preformance...it really does
deliver images on a par with my Takahashi 4", but much brighter. I
think the contrast may be just as good as the Tak, but to be fair, it
would require a side-by-side comparison to really evaluate that.
Sometimes you'll see one of these scopes pop up on Astromart or
Craigslist. I picked mine up on Astromart for about $750.00. I really
don't think there's a scope in my inventory that delivers this much bang
for the buck. I can't wait to try it on Saturn and Jupiter--and Mars in
'07.
Regards,
Uncle Bob