I got myself a SK80ED, a used one. Set me down by €350 + €40 for "beugels" (brackets). BTW, it requires ,,böööchls” for a 102mm achromat.
Some daylight testing revealed: great little thing! Just it's not really small, and it's weighing quiet something...
Performance, tested it with 2" and 1¼"
EP, starting 50mm (!), ending with 10mm and the 3xBarlow (would
result in a magnification of about 200x). Unfortunately GSO and Synta
do not seem to be compatible. I've got a set of GSO 2" EPs which
refuse to slide into focus, now it comes, the Synta-scopes have not
enough front-focus when a 2" diagonal is installed. My Synta 2"
EPs are, on the other hand, working just fine.
Very very smooth
focusing with a Crayford.
Talking about the Crayford, it was not properly adjusted, with the tension screw completely unfastened it was still really tight. Thus, taking apart, cleaning, adjusting, reposition the Teflon® foil fixed the problem.
The ,,Sijthoff''-building was used for testing... went to the scopes maximum magnification (80mm -> 3.15") of 60x3.15=189 (EP 10mm + 3xBalow @ F=600mm). On stars I will be testing beyond the limit... whenever the "new telescope(s) curse" is over. My SK80ED is now sitting on the H-EQ5 waiting for sky.
Update I:
The curse let me off the
hook for a couple of minutes.... Mars already showed structure using
3xBarlow and 10mm (super wide angle) EP. Still it was very bright, I
guess a filter could help. No false color as far as I could judge.
My apologies to GSO, I could focus M45 with all three (SuperView,
Wide View Five Elements - gosh, what a name) EPs. 50mm left me about
0.5mm "front focus", 42mm and 30mm left (logically) a
little bit more. Worth to be mentioned that the by far cheaper Synta
32mm and 26mm EPs find focus with about 2cm of "front focus"
using a diagonal.
Even with the 2" focuser nearly fully
retracted there is no vignetting. Well, give it a go, simple
arithmetics, the damn thing is a 3.15", having 600mm focal
length.... Hint: consider geometrical optics.... Forget about Mr Abbe
for a second.
Little more on EPs: Since my visus is still quiet
good, no spectacles, I consider my focus settings as "infinite",
thus, one wearing correction glasses might run into troubles using
the GSO EPs. However, the GSOs have quiet some eye-relief, allowing
for vision corrective optical elements being in the light path.
You want to use a mount such as the H-EQ5 or
heavier. First, the instrument is rather heavy, secondly the 2"
accessories do have their weight, thirdly despite the small aperture
of just 8cm the scope seems to allow for high optical power. There
was not enough hole in the cloud, thus, no time to point onto a
bright star or a double for deeper study of diffraction
rings/pattern. However, there were some diffraction rings around
stars, looking quiet ok....
Can't wait to attach a webcam to the
gizmo and let the CCD tell me more about aberrations.
Update II:
Now that the curse is
back on it's duty, I found time to improve the focuser, as indicated
on the www (on the orion 80ed which is identical anyway). The focuser
pin left traces on the "flat" surface indicating that the
surface was not as flat as it should be, on some places the pin
seemed to have had contact with only the outer edges, not really what
was invented.... Solution, as proposed, grinding using a grindstone.
Did that for about 1h. Movement is quiet tricky, very short strokes,
making sure not to add curvature to the surface. OK, the grinding
results in removal of the anodization, which is a pitty since
anodized Al looks sooo nice. Anyway, the focuser is now, with the
same amount of stress on the pin, more frictional. Traces show that
the pin now is in contact with much more surface area of the flat.
Not yet perfect though, but much better.
On the Inet it further is suggested to replace the pin with one having a larger diameter, I am not quiet sure what this is good for, since doing so will change the gear ratio a less desirable value. I'd rather chance it so smaller diameter, which would sacrifice traction, thus, also will be no good....
Update III:
Todays cloudless hour
(5pm-6pm) was usable for tests on Venus and Moon. As promised, this
was the turn to toughly test the tiny telescope, i.e. pushing it to
and beyond the limits...
Venus quickly hide itself behind tress,
but, there was enough time for a short glimpse. Nice crescent, clear
edges. Started 15mm (GSO), next step: adding the 3xBarlow, both
setting gave a nice result. Further increasing magnification I put in
a 6,4mm SuperPlössl (Meade 4000), again very pleasing result, no
color yet. BTW: We are talking about a magnification of 280! Venus
disappeared.
Next target: Moon. I left the setup as is. Short walk
over moon's surface... Following test, now pushing beyond: 3xBarlow +
2xBarlow + 6.4mm. Now were talking about 560x, which clearly is
beyond what's usable with 80mm aperture. And, in fact, things got
mushy. Back to reasonable: 3xBarlow with a 4mm Kellner, still this
should be a little too much (450x) for the scope, but... at least for
structures on the moon, it was not. A intra-focal structures became a
slight red haze, extra-focal this haze became blue, in focus no color
what so ever.
Update IV:
Some more hours (!) of
clear sky. Now we're talking... Mars, nicely high in the sky, very
good transparency, seeing quiet ok. Thus, point the scope to Mars.
Tests are now concerned with the maximum possible magnifications and
the eyepieces to obtain these. After centering Mars, the 3xBarlow and
the 4mm Kellner were sent to action resulting in a crisp clear image
of the planet. Clearly structure was visible, still Mars was quiet
bright. This test was about EPs, as mentioned above, therefore the
next candidate found it's way into the Barlow: a 4mm SuperRamsden
(SR). Since a Ramsden design is nothing but a better Huygens, there
was not so much to be expected. I was not disappointed, the image in
fact was more blurry than the one obtained by the Kellner. Next test:
replace the 4mm SR with a 4mm MA (modified achromat). A “modified
achromat” is supposed to be an improved Kellner, but is it?
It's different, but it is not improved... The 4mm MA in fact gave the
worst image of all.
Back to the 4mm Kellner, now testing on
filters. It appears that most important for better visual impression
is the reduction of brightness. First filter to join the game the
“Baader Nd-Sky-Glow” giving a good result. More or less
the same result with the “Baader Contrast Booster”. The
Nd-filter provided a more “red” appearance. It's hard to
tell which gave the nicer result.
Enough of high optical power
stuff... M45 nicely visible, thus, chance of EP, 40mm Plössl
(Celestron). Very very very impressive view, even through a 1.25”
back-end. A little bit of negative distortion, no wonder... Same
experience with a 32mm Plössl (also Celestron), less distortion
though. In either case I could not visually constitute coma.
Now,
going for the star individually, increasing magnification. The 4mm
Kellner on stars, and, in a second step boosted by first a 2xBarlow
and than a 3xBarlow. Nothing to complain about! Nice Airy-discs, nice
diffraction rings, symmetric, concentric, in one word: perfect.
I
intended to split some double stars for testing, the sky however was
not fulfilling my wish for more and decided to close the cloud-cover
again.
Last modified December 10th 2005