New fellow in my telescope collection. Why
an alt/az-scope of this kind? First reason being the not so good
weather in my place, the second being mobility.
The weather call
for QuO-QuI operations! No, this is no Latin, even when looking
alike. It's supposed to mean quick out, quick in, just as needed (to
be mentioned that the scope will be stored in a cold place,
reducing cool down time dramatically). QuO is also linked to mobility
in a way, no lumpy gobbets in a Dobsonian mount, in contrast to a GEM
having all this gizmos such as tripod, counter weights, clamps,
brackets and what not. OK, you might think this dude is into
photography, but... not only, gazing is nice too! Finally the OTA is
light-weight enough be allow mounting on a heavier equatorial mount.
So, what about the QuI, the quick in? Well, that's really weather
related; guess what, I don't want any of my scopes exposed to water
doplet falling off the sky! We got a lot of rain here in South
Holland... but not necessarily continuous all the time.
So, I got
myself a "low ohmic", used Helios 8" f/5 (aka
SkyWatcher Dob 200mm/1000mm).
A first test the early (4am) morning of
Feb. 1st 2005 revealed an utterly devastating result. Any
object I looked at was a disapointment, all sorts of optical effects
you certainly do not want to know about. I roughly checked
collimation the day before, using a Cheshire "eyepiece".
Collimation seemed to be off by a bit, but not totally.
After
a hard days work (in my job), the decision was made to check closer
on collimation of the scope. Yes, it was off... but there was no way
to get it collimated... Why's that? The scope can't be as crappy not
reaching collimation, not even closely.
Hunting down the reason
took about a quarter of an hour, here it comes, simple as is. The
(rather heavy) mirror cell mounted with six (6) screws to the
scopes metal tube. Generally this makes sense.... BUT, the rear
end of the mirror cell was showing a gap to the tube of about a
finger nails thickness, whilst the "rocker box inside" end
was tight close to the tube. Ahaaaa! Setting the scope (w/o the
rocker box) to the ground, loosening all six screws, slightly shaking
the tube back and forth on the mirror cell and re-tightening the
screws solved it all. The scope could now be collimated within
minutes.
After dark, the sky cover was willing to
accept some perforations... QuO! Now, wow, that's what it would be
alike... Gazing around just surfing the sky was quiet impressive, M42
was showing a very nice structure in direct vision, even when using
the very cheaply looking "20mm Super Wide Angle" eyepiece,
from which I have not expected anything good. The other eyepiece that
accompanied the scope is a, guess what, "10mm Super Wide Angle"
in which the structures were really coming out nicely. Changing to
Meade series 4000 Super Plössls (down to 4mm focal length) gave
first impressions what could be possible in dark places... I
only used 1,25" EPs, as none of my (cheap) 2" EPs
could reach focal condition with the adapter provided with the scope.
Intra- and extra-focal tests revealed very good
results...
Collimation really did the trick, somehow I am not so
surprised after all. I am just glad that the scope performs the way
you could expect from D=200mm f=1000mm optics.
The focuser is not brilliant but OK, some mods could certainly improve this contraption. The same applies to the smoothness of the mount, i.e. rocker box (there are webpages out there in cyberspace indicating relief). The f/5 tube is short enough to allow shorter persons (kids) comfortable observations. Personally I have to use a small stool for sitting obs, as I am too tall for comfortably reaching EP whilst standing.
I got the scope for €300. After collimation I now think the setup is really worth this "amount" of money, at least I would buy the same scope for the same price again.
More to follow...
Here it comes, another evening (Feb. 3rd
2005) with some cloudless moments.
Saturn, good to test on, also
quiet high in not too late hours. For the observation I used a Meade
series 4000 Super Plössl with 4mm focal length (giving a
magnification of 250x). On the planet itself two belts were showing
off. Saturn's ring system exhibited the Cassini division all around
the visible portion, a sharp shadow thrown by the planet was placed
on the rings, the rings outside Cassini's division were clearly
darker than the inner rings. Definitely identified moons were Titan,
Rhea, Tethys, Dione and Mimas. For a focal length of just 1m from a
light polluted place, I guess the result is not too bad at all...
Further tests on stars, Sirius, Rigel, Betelgeuse and Procyon
were supposed to assess the collimation and the performance of
different types of eyepieces on the scope. Seeing btw. was somewhat
ok this evening, transparency and cloud cover were a different story
though. Diffraction rings on Sirius were about perfect when using
Meade SP 4mm and 12.4mm, infra- and extra-focal as well as in focus.
The collimation I did on February 1st obviously was
successful so far. My next point might certainly is a matter of
taste... diffraction pattern of spider vanes. The spider vanes are
made from sheet metal, quiet thin... causing very explicit
diffraction pattern. This is why I like unobstructed systems such as
refractors.
Now, something less positive, the provided “Super
Wide Angle” EPs. I am not quiet sure what on these eyepieces
shall be super... at least I could not find anything. Or, to
phrase it differently, they simply do not fit to the scope at all!
The coma of the fast Newton-reflector was very prominent in the
“Super” (not noticeable with the Meade EPs at all), the
contrast muddy and the position of the observer's eye extremely
critical. I guess the best function these “Super”
eyepieces can have would be being source for parts needed to build
webcam adapters with filter threads.
QuO-QuI worked perfectly; this time a used a garden chair for increasing my comfort. It is about time to mount the Rigel QuickFinder... but this is another issue.
Update, February 15th 2005, one
hour of relatively good sky. One of my favourite objects is standing
high in the sky, h and χ
Per... beautiful! I enjoyed the view for quiet a while...
The
cores of M31, M32 and M110 were nicely visible, not much of M31's
structure though, I guess the fainter parts were all drowned in local
light pollution.
Time for some more testing: What about filters?
Three different filters being able to fight light pollution are
living in my astro-box: Baader Sky-glow, Baader Contrast Booster and
Astronomik CLS. The latter one could not tested that night, clouds
turning in again. So, let's have a look at the two Baader filters,
both mounted on 10mm EPs. The Contrast Booster creates a greenish
image, not so nice... but for sure only if the object is bright
enough to trigger the cones of the eye (colour vision); for fainter
objects, triggering the rods only (sensitive at about 500nm) this
actually helps. Again I went for M42, the Contrast Booster took away
quiet some of the light pollution and at the same time was able to
show more detail of the bright nebula. Compared to that the Sky-glow
filter was equally able to fight light pollution, but this filter
could not recognizable enhance the detail of M42, at least not as
much as the Contrast Booster. Conclusion, emission nebula are easier
to observe with both filters, both usable, I would prefer the
Contrast Booster. Back to Perseus (Double Cluster), just to confirm
what I guessed; both filters are taking away a (un)fair amount of
fainter stars. Unfortunately clouds started covering the sky, so
there was no chance to figure out which is the worse one. After all,
no real surprise, but a slightly astonishing result concerning the
Contrast Booster, which I believed being mainly helpful for planets.
Both filter are based on Neodynium (Nd). According to the
transmission curves both filters have a transmission of just 80-90%
at 500nm.
Last modified Feb. 15th 2005