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Transcript
Bushnell North Star 127mm
Maksutov Cassegrain review
(September 27, 2006)
I am certain there are cheap hobbies, but I’ve yet to find one. At least that’s what my
spouse of 41 years has concluded. So when I revived an interest in astronomy in the fall
of 2005, in an effort to enjoy the Mars opposition in October of 2005, she could breathe a
sigh relief: I already owned an Astroscan 2001 4.25” reflector telescope, which I
purchased 6 or 7 years before. Admittedly, it was better than the Jason 60mm refractor I
had bought in 1986, which turned out to be unsuitable for seeing Halley’s comet (the
smudge in the sky), yet it wasn’t as good as the Odyssey 13” reflector, which arrived too
late to resolve “The” comet (at this time, I no longer own the big reflector – had to sell it
to buy college supplies for my eldest son many years ago).
But the Astroscan did not resolve Mars as I thought it should have. Even with Edmund
Scientifics’ bulky Barlow lens, and some very good viewing conditions, the red planet
revealed none of the south polar cap, none of its dark surface markings. But in the
interest of economy and paying Christmas bills, not to mention the cost of the Ping G5
golf clubs I had recently purchased, I suppressed my thirst for seeing celestial objects
with clarity.
Subscribing to Astronomy magazine, with its glossy photographs of the new Meade and
Celestron hardware, plus an Orion catalog which came with a new telescoping eyepiece I
had ordered in an effort to resolve Trapezium, did not quench my appetite for a new
scope. But then, during the Tulsa Astronomy Club January sky watch party, we were
treated to two different 16” reflectors with 2” eyepieces, and witnessed a knockout view
of Saturn (the likes of which we had not seen since visiting the Griffith Observatory in
Los Angeles 20 years ago). I then knew I had to have a new scope.
My objective was cost driven: could I find a telescope which would mimic the giants we
had been treated to in January, but which cost less than $500? I needed as much focal
length as possible, with lots of light collecting ability. Thanks to internet searches, I
happened upon a Bushnell 127mm Maksutov Cassegrain, which boasted a mammoth
1550 mm focal length, a go to mount, and a couple of eyepieces. Since Bushnell doesn’t
advertise in Astronomy magazine, I had to judge the quality of the company by other
factors: I enjoyed the Bushnell distance-laser finder binoculars for use on the golf course.
That unit had given me fairly accurate distance readings, and therefore suggested
Bushnell made good optical products. The only product review I could find on the
telescope was a short blog: the mount sucks! Telescope has great optics. I had to
disregard that blog.
So I took the plunge, and in a matter of days, received my order. The entire unit was
packed in a long, heavy box, which I have retained for possible warranty claim purposes
(the unit has a limited lifetime warranty). The tripod has heavy duty legs (which I
lubricated with oil, so they would slide more easily). The mount is described as being a
Kinematic Mount; it holds the telescope in place with an “arm”, and is basically an alt-
azimuth unit (but with the motor, tracks objects much like a motorized equatorial mount).
The GoTo computer is powered by a 9V battery, which seemed a bit lightweight
compared with other go to units offered by Meade and Celestron. But I had to accept its
engineering, because my purchase was cost driven.
The Tripod
The two eyepieces furnished with the unit, a 4mm and 25mm, should be all that was
required for my purposes, but I had backup eyepiece from Edmund (the 28mm RKE,
which I later judged to outperform the Bushnell 25 mm eyepiece), as well as a zoom 7 –
21mm eyepiece from Orion, a 40mm Celestron, a 7.5 mm and 14mm from Orion, just in
case. In addition, the Bushnell unit was also furnished with a red dot finder scope.
The Red Dot Finder
The English portion of the manual (which is printed in 6 languages) is only 32 pages in
length, half of which is instructional, the other half devoted to listing Constellation
abbreviations, Messier objects, and names and numbers of stars. Although it may not be
fair to compare the Garmin Street Finder manual with this one (after all, getting to know
and use a GPS device is ostensibly a bit more difficult than learning how to operate the
Go To features of a telescope), Bushnell has not done a poor job in explaining the
variables of the Go To features in its “North star Motorized Go To” system.
But as the editors of the Garmin GPS manual suggested, the best way to learn the Street
Finder GPS system is to use it. I suppose the Bushnell technical manual writers had the
same philosophy, but they did not mention that concept in the manual.
Fate was with me for 2 days, for the skies were clear and the weather not too cold. Armed
with a variety of red flashlights, including one which strapped to my head (made for
hunters; purchased at a hunting supply store), my Palmone TX with the Planetarium
program (which provides a very nice portable sky atlas)i , I ventured to my secret
observing place near the expressway, and set the unit up in about the same time period it
takes to put the Astroscan on its tripod: the Bushnell tripod is locked in position by a
plastic tray, which twists into place; the tray has several 1.25” holes for holding
eyepieces. The scope slides into a loose fitting sleeve on the tripod arm, and is secured by
a hold down screw, which initially caused me concern (with the scope pointing at an
angle approaching zenith, I was apprehensive that it might slip out of this housing; that is
not an issue, for the hold down screw keeps the telescope safe from slipping, even at an
unusual angle). The hold down screw worked fine, and the telescope has never slipped
from the mount.
The red dot finder scope works all right, but after the first couple of nights, I removed it
and replaced it with my Rigel Quickfinder (which I had purchased for use with the
Astroscan). With the Rigel, I don’t have to tilt my head and bend as much to locate
known objects.
Scope with Rigel Quickfinder
To insure the mount is level, I purchased a round carpenter’s level, which I attached to
the plastic tray used to lock the mount’s legs into position. The unit works better when it
is level with the ground, and carpenter’s level is very useful in that regard. In addition, I
purchased a digital compass, and before I begin the alignment procedure (described
below), I attempt to align the direction of the telescope “north”, using the digital
compass. I have also used a traditional compass in this alignment process. The reasons
for the alignment will be explained later on.
The GoTo features require that I sight on two stars from a list of stars selected by
Bushnellii . By using this technique, it is unnecessary to input the time of day, time zone
and location. If one is careful (and very fast in alignment the telescope) in sighting two
stars, the control device (and voice recording, which is hard to hear if there is much wind
about) will indicate the accuracy of the calibration, which is more accurately described as
triangulation (a 5 ***** rating is the best). From that point on (and the set up time for
calibration can take several minutes), the GoTo unit is theoretically capable of pointing
the unit to planets, stars, nebulas, and constellations. The problem with this technique is
that of timing. Because the stars are in motion (due to the earth’s rotation), it is very
difficult to locate two stars, then enter that data on the hand held computer control, within
a 2 minute span; the end result is that most ratings are 1 *, which means, the accuracy of
the Go To features is marginal, at best.
To my knowledge, no telescope will capture the entirety of any constellation, and this
makes me wonder why the Explore mode even offers the ability to slew to a
constellation. Perhaps the toy binoculars I bought for my grandchildren would permit me
to see part of a constellation (magnification power of about 1.2), but that is a stretch. The
unanswered question still remains: why offer a feature on a GoTo unit which has no
practical application?
GoTo features are drawing cards for any computer driven telescope, and I want to give
some additional impressions of the Bushnell mount and GoTo computer features. To
make the unit function as designed, it is essential to have a fresh battery (and I am led to
believe this is a universal requirement on all GoTo systems; none of them work well
without fresh batteries). It is very important to achieve a 5 ***** rating indicated on the
hand held control unit. A 3 *** rating, which will not produce accurate alignment by the
computer, is not acceptable: every user should start the process anew, until you achieve a
5***** rating.
Stated differently, and when I first purchased the unit, whenever I was given a rating less
than 5*****, I kept on aligning the telescope to more stars, until I finally achieved 5
*****. After attaining that alignment (or even a lesser rating, such as 1 *), I used the
40mm eyepiece, which gives a wider field of view. I can then direct the Go To computer
to find a given star, e.g., Sirius. Once selected, the system rotates (slews) to the desired
object. Using a narrower field of view with the 25mm eyepiece does not always locate
the object I was seeking; however, I was always able to locate the object using my 40mm
eyepiece, which permitted me to switch lenses to 25mm, 14mm, and 7.5mm (the unit
only comes with a 25mm and 4mm eyepiece; you will have to purchase other eyepieces,
which will provide greater versatility and greater magnification).
There are six settings on the hand computer (besides the align earth setting, which is used
for triangulation purposes): Explore, Telescope, Sky Tour, Identify, Align Object, and
Align Star. Each function has a sub menu, which can be used for aligning the telescope to
RA and declination., stars, constellations, planets, stars, and what I consider to be
moderately deep sky objects. The function known as “identify” which permits me
manually to find an object, then tell the computer to identify whatever I have pointed the
telescope to see. By doing this (which requires that I press the “Go” button on the
handheld control), the computer will invoke an equatorial tracking feature, which keeps
the object in sight without any further realignment on my part. Stated differently, if you
are in the “identify mode”, once you find a desired object and press the Go button, the
computer will track the object, as the earth rotates (this tracking ability does not work
with all functions, however).
At this phase of my career, I have cataloged about 30 stars, Messier objects, and other
“favorites” (as recommended in the writings of Bob Berman and the author of Turn Left
at Orion), and am working my way down the list. Last night my objective was TX
Piscium (19 Psc Flamsteed). The telescope does not have this star in its data base, so I
had to use the palm pilot program (Planetarium) to give me the coordinates in the sky.
Through a combination of the azimuth and altitude readings from Planetarium, my digital
compass, my binoculars and some guesswork on my part, I was able to locate the star in
the Bushnell. The technique in locating the object is a bit complicated, but here it is. The
telescope is switched to “telescope mode”, which displays RA and declination, as well as
alt/azimuth. I am not skilled enough to use the RA and declination readings (and they
aren’t always accurate, because this is not a GPS GoTo system). I manually moved the
telescope to that part of the sky where I thought TX Piscium was located. At that point, I
used the hand held computer control, and moved the unit up and down, and left to right,
to adjust it to where Planitarium said to look. Using this trial and error method, I found it.
Last week I used the explore function to locate Neptune and Uranus (which are on the
computer’s database), then switched to telescope mode, to locate the exact position of the
planets. The computer will not give an equatorial “track”, however, when it is in
“telescope” mode, which means, I had to use the up-down, left-right buttons on the
computer control, to keep the planets within view (as the earth rotated).
The hand control’s arrow buttons permit me manually to move the telescope’s alignment
(I can do the same thing without using the handheld unit; however, the motorized unit is a
bit easier to move than trying to do it with my hands, which don’t always work as well
when the weather is cold).
Handheld Control
Last spring I was able to adjust the scope, so that I could view Saturn and its rings with
clarity (it was not able to detect the Cassini division; but it still outperformed the
Astroscan’s resolution by leaps and bounds). The computer permits me to focus on
different areas of the sky, and I will be given a read-out of the name and location of
wherever the telescope is pointed, which is what Celestron’s new pointing device is
designed to do (Bushnell gives an audio narrative, which is difficult to hear if the battery
is low). The accuracy of the information on the handhold control is marginal, because of
the alignment problems (mentioned earlier).
The star diagonal which holds the eyepiece is very good. I was able to remove and insert
different eyepieces without juggling the mount or disturbing the view. In addition, the
focusing knob is very smooth, which was a dramatic improvement over the focusing
knob of the Astroscan (twisting the Astroscan’s focusing knob requires so much torque, I
sometimes push the scope out of alignment, which requires that I re-locate the star I was
viewing).
The factory star diagonal is removable, which permits substituting other diagonals. I have
not taken the scope to a telescope store to determine if that is feasible. In addition, the
scope could probably be mounted on another GoTo tripod, but again, that requires a trip
to a telescope store with a good inventory of tripods (and I haven’t had the luxury of such
a trip), and the purchase of more equipment.
Because viewing comparisons are useful, I placed the Bushnell side-by-side with the
Astroscan, and tried different eyepieces with each unit. My initial test object last spring
was (unfortunately) the full moon. Both telescopes resolved very well at 28mm and
25mm. Using the zoom eyepiece from Orion, the Bushnell produced fuzzy resolution at
7mm, as did the Astroscan – magnification at 15mm was clear with the Bushnell, but the
view was too close for viewing (at 15mm, the Astroscan, which has a focal length of
445mm, gives 30x magnification; this is about the maximum useful magnification for the
Astroscan – that same eyepiece produces about 100x magnification on the Bushnell,
computed as follows: focal length 1550mm 15mm eyepiece = 100x magnification). I
should probably sell the 4mm Bushnell eyepiece in a garage sale, because it is a deep sky
eyepiece, which requires precision from the GoTo system (which is not available on this
tripod). The Astroscan at 4mm provided only fuzzy resolution.
Although this review is not of the Astroscan, I should make a parenthetical comment on
the metal view finder which comes with the Astroscan: it is useful and fairly accurate. It
is not as accurate as the Rigel Quickfinder, which I use with the Bushnell.
So there you have it. The Bushnell is a bargain space scope, with very good optics (the
scope resolves what I regard as a deep space object, such as Trapezium, with very good
clarity – one can view M27, the Dumbbell Nebula, but its light gathering abilities are not
as good as larger scopes, so you will need very dark skies to produce a satisfactory
resolution). My objective was achieved, which was to simulate the views of Saturn I had
experienced with much larger scopes, but to do so at a price under $500. The unit is
portable and easy to set up, and is probably best suited for planets and bright stars, but
not deep space. The GoTo computer features require some practice and perhaps use of
other eyepieces, to locate desired objects.
And I did buy my wife some flowers after the unit arrived.
Scope Without lens, mounted on tripod
i
No one can ignore Celestron’s GPS planetarium, but the Palm Pilot program might be more worthwhile, at
least for those of us who do not like taking paper star guides with us, and who don’t know the placement of
stars, constellations, and deep space objects. For example, the planetarium program gives me the general
location of stars, planets, nebulas, and other deep space objects. For example, once I determine that M1 is
visible for viewing (which I can see from the Palm Pilot program), I can use the RA and dec. coordinates
on the Bushnell “telescope” feature, and slew the unit into the right position. As you can tell from the tenor
of this article, my purpose is to explain that the Bushnell doesn’t come fully equipped, but that by using
other resources, such as the Palm Pilot program, Planetarium, and other eyepieces and locater devices, it
can be transformed into a very workable telescope system.
ii
The following list of stars are the ones to be used for triangulation – oddly, only 17 of the 26 choices are
in the list of brightest stars: spica, suhail al muhlif, vega, vachernar, acrux, al nair, albireo, aldebaran,
alphard, alpha (but which alpha star we are to choose, not hint is given: are we looking for alpha antillae,
alpha arietis, alpha bootis, et al?), alpheratz, altair, antares, arcturas, Betelgeuse, canopus, capella, casor,
deneb, denebol, fomalhaut, mifak, mizar, navi, polaris, procyon, rasalas, regulus, rigel, Sirius, spica, suhail
al muhlif, vega.