The lure of a hyper-portable refractor

Apochromat at f3.5 or so produce images as "good" (details) as an
achromat at f8? Say, for a scope of 100mm? If so, I can see a market
for hyper-portable 4" refractors producing acceptable image quality.
If the scope could support say 150x (like a 4" f8 achro) before degrading,
it would be a fantastic. I've used the lens from an 80mm ED spotting scope
that produced decent views of Saturn with low colour error levels up to
about 170x (4.8 Nagler + 2x barlow). Certainly much better than an 80mm
f5 achro and the focal length of the lens from those spotters is around
425mm or f5. The scope with a 2" focuser was only a foot long. A triplet
100mm (as opposed to the doublet EDs in the spotters) at f3.5 would be
even shorter, and very easy to mount, even with the extra weight.

I think this would be a great market. I bought a couple of the ST-80s and
wasn't enthralled with them. The mechanics were poor and the views were
just ok. I sold those and bought an ED80 for those days when I've got a
spare 15 minutes and don't want to waste time with setup and tear down. I
think it's a great scope for the $$$. The mechanics are pretty good, the
optics beat my expectations (after a little collimation procedure I did on
it) and the color is almost negligible (although note, I think I don't see
as much color in the blues as others do, as my friend noticed color on
Altair at about 100x and I did not. Overall, I'm very pleased with it's
performance and it's right on the edge in terms of portability. With my
40mm MK-70 I get a 4.5+ degree field of view, which is more than enough for
me (makes a great finder...maybe mount it on my big dob someday!)

Mike.


"Richard" wrote in message
om...
Apochromat at f3.5 or so produce images as "good" (details) as an
achromat at f8? Say, for a scope of 100mm? If so, I can see a market
for hyper-portable 4" refractors producing acceptable image quality.
If the scope could support say 150x (like a 4" f8 achro) before degrading,
it would be a fantastic. I've used the lens from an 80mm ED spotting
scope
that produced decent views of Saturn with low colour error levels up to
about 170x (4.8 Nagler + 2x barlow). Certainly much better than an 80mm
f5 achro and the focal length of the lens from those spotters is around
425mm or f5. The scope with a 2" focuser was only a foot long. A triplet
100mm (as opposed to the doublet EDs in the spotters) at f3.5 would be
even shorter, and very easy to mount, even with the extra weight.

my friend noticed color on
Altair at about 100x and I did not

Eyes vary when it comes to seeing color error. As you age, you will have less
sensitivity to blue at night. Yellowing of the eye lens is usually the cause
(built-in minus violet filter).

Roland Christen

"Chris1011" wrote in message
...
my friend noticed color on
Altair at about 100x and I did not

Eyes vary when it comes to seeing color error. As you age, you will have
less
sensitivity to blue at night. Yellowing of the eye lens is usually the
cause
(built-in minus violet filter).

Neat, didn't know it was doing that. It makes me sad though, my friend is
older ;-)

Mike.



Roland Christen

(Richard) wrote in message . com...
Apochromat at f3.5 or so produce images as "good" (details) as an
achromat at f8? Say, for a scope of 100mm? If so, I can see a market
for hyper-portable 4" refractors producing acceptable image quality.

Although it's possible to design 4" f/3.5 true apos, these designs are
usually unpractical due to tight tolerances and the presence of exotic
glasses.

(drv) wrote in message . com...
(Richard) wrote in message . com...
Apochromat at f3.5 or so produce images as "good" (details) as an
achromat at f8? Say, for a scope of 100mm? If so, I can see a market
for hyper-portable 4" refractors producing acceptable image quality.

Although it's possible to design 4" f/3.5 true apos, these designs are
usually unpractical due to tight tolerances and the presence of exotic
glasses.

I figured that for true apos, but even if it had colour correction like
that of a standard 2 element ED or thereabouts, it would be an
improvement on the Shortubes.
-Rich