Outward Appearance of the Astro-Rubinar system:
The Astro-Rubinar is a catadioptric design; but
it is not a Maksutov or Schmidt telescope. The system includes
three full aperture lenses, a primary mirror, a rear surface secondary
mirror and a small field flattener lens. The secondary mirror
is affixed to the outermost aperture lens. A set of two full aperture
lenses is situated between the secondary and primary mirror. The
primary mirror is spherical. The field flattener lens is situated
in the optical back, behind the primary mirror. The central obstruction
of the secondary mirror is 13% of the area and 34% of the diameter
of the clear aperture. Light passes through 18 optical surfaces
and reflects off two mirror surfaces on its way to the eyepiece.
The reason for all of these optical components was to create an
excellent flat photographic lens. However, it was discovered that
the quality of the components created a good telescope that also
has very good near focus capabilities.
Included with the scope is a certificate asserting
that the wave-front error (p.t.v.) of the optical system is ¼
wave at 555 nanometers. This certificate is signed by by Mr. Bill
Burnett (proprietor of ITE) and by Mr. Mike Palermiti (optical
systems evaluator). That the end product is diffraction limited
is amazing and a testament to good optical work on the individual
elements and good mechanical work on the overall assembly.
The lens mirror alignment creates a light compact
optical tube assembly. The scope is 7 inches long with the dew
shield and diagonal removed. It weighs just over 5 pounds (2.5
kilograms). This solid metal OTA is painted black with etched
in markings. With both attached, the unit is about a foot in length
and about 5 inches in diameter.
The scope is attached to a camera tripod or to an
equatorial mount by means of a ¼-20 fitting. This fitting
is attached to a ring of metal that is affixed to and encircles
the scope near its visual back.
This unit has a number of cosmetic imperfections.
The metallic ring has a roughened-up look to it; a number of striations/scorings
which have been painted over. Further, the markings etched on
the scope have a rough though uniform appearance. Finally, at
the very edge of the field-flattening lens is a small chip/crack.
This appears underneath or right next to the retaining ring. The
chip is perhaps 1.5mm by 1mm and can be seen reflected off the
field-flattening lens. However, when light is blocked from reaching
the chip, the reflection is removed from sight.
A very long baffle tube extends most of the way
from the primary mirror central hole to the secondary. Within
this tube are many baffle-edges. All interior surfaces have a
dull black appearance.
Performance (optical):
The scope has been tested by Mike Palermiti for
ITE and a wave-front error of ¼ wave at 555 nanometers
has been ascertained.
Appearances of intra and extra focal images of bright
stars and of point light sources are strange, even disturbing
to the non-optician who has become accustomed to MK, MN or apochromat
optical systems. The intra-focal image is a sharply defined elliptical
structure with a well-delineated ring forming the very perimeter.
The extra-focal image is mushy in comparison, lighter in tone,
and elliptical as well. The elliptical shape of the intra focal
image is perpendicular to the elliptical shape of the extra focal
image. This is an indication of astigmatism. The use of Cor Berrovoet’s
Aberrator-software indicates that the astigmatism of this particular
scope creates a wavefront error of between .248 and .276 wave-front
error. At a high degree of de-focus both the intra/extra focal
images present nearly identically shaped and distinct double rings.
Such astigmatism, according to expert opinion, does not compromise
the diffraction limitation of this system; either its ¼
wavefront error or 80% strehl ratio.
There are no easily accessible means to collimate
the scope. However, the collimation seems to be very close to
dead-right-on collimation with only a slight loss of the doubled
aspect of the ring-pair in the greatly defocus intra-focal image.
The in-focus image of point-light-sources, when
the air is stable and when the scope is thermally equalized, presents
a round airy disk and a single diffraction ring of uniform size,
uniform distance from the airy disk and uniform brightness. Quite
often, the continuity of the diffraction ring is disrupted by
four tiny black notches, each 90 degrees away from the next. Sometimes,
the diffraction ring is continuous.
The scope functions well on terrestrial objects,
providing pleasant views of distant objects and sharp, clear,
flat views of objects as near as 14 feet whether the system is
used with a diagonal or straight through. This is a bit longer
than the advertised near-focus capability of 4 meters (13 feet).
During times of ambivalent sky stability, with a
limiting zenith magnitude of 4.5, the scope reveals stars of magnitude
13.0 with averted vision at 300X (75X per inch). The Great Nebula
in Orion gives a very satisfying appearance through a 17mm plossl;
as aesthetically pleasing as seen through an MK67. The appearance
of the epsilon lyrae double-double is greatly superior to a Celestron
F5 80mm achromat refractor and somewhat inferior to the view through
the MK-67. Albireo and gamma Andromedae give color saturation
views more like an F5 80mm refractor than like the MK-67. In a
somewhat stable sky, Castor’s two components can be seen
at 50X, though the companion of Rigel is not visible. In a stable
sky, eta orionis which is listed as a double whose components
are a full magnitude different separated by 1.5 arc secs, is easily
resolved; the fainter of the two nestling on the diffraction ring
of the former. In a borderline-stable-sky, one can see detail
within sunspot penumbra, easily see faculae and detect the presence
of rice grain. In an unstable sky the Cassini division of Saturn
is detectable but not what would be called, visible. In a stable
sky, the division becomes detectable at 90X and visible at 220X
(55X per inch) as a faint vague pencil thin line. At moments of
good stability the division can be detected through nearly the
whole ring, and at moments of very good stability becomes readily
apparent. On the moon and on planetary detail, best visual acuity
is accomplished at between 20X and 30X per square inch of aperture
(80X to 130X in this system) as is true for all telescope systems.
Accordingly, though higher magnification may provide more pleasing
views of a few objects due to an enhanced image scale, no additional
detail can be observed above 130X, even with good orthoscopic
eyepieces. Only slightly more detail can be seen at 130X with
a good quality ortho, than at 95X with a fair quality plossl.
There appears to be no chromatic aberration at all. None was observed
at the terminator of the moon bright planets or stars.
Astronomical views are always dependent on atmospheric
stability and thermal equilibrium within the optical system itself.
Due to the number and arrangement of the optical components within
the system, it can take up to 45 minutes for the scope to “cold
soak.” Of course, should the temperature be dropping, “cold
soak” may take longer or may be repeated.
This system provides completely flat field-of-view
images. In all the plossl and orthoscopic eyepieces the field
is flat edge-to-edge. Images are focused clear across the field
of every eyepiece from the 32mm plossl to the 4mm ortho. When
looking at objects with a straight lined edge near the perimeter
of the eyepiece field of view, the line seems to curve away at
the ends of the line. This may, however, be only an optical illusion
of a line approaching a curved arc-shaped concave edge.
Another very attractive feature for those stargazers who are also
scopists, is that extremely sharp images can be obtained of nearby
objects. At the near-focus of 13 feet, the level of detail revealed
is such that this system can be characterized as a long-distance
microscope.
Another outstanding feature is that there is no
glare in terrestrial views. This is probably due to the extensive
baffling, to the flat black paint and to the optical design. Even
at 100X per inch and above, no glare was seen. As a comparison,
in the C-90, intrusive and distracting glare appears at 40X per
inch and greater. The situation with astronomical viewing of bright
objects is somewhat different, though the contrast is very good.
When gazing at a gibbous moon, at only a short distance from the
dark terminator the field is flooded with a decidedly bluish glare.
Again, it does not impact the view of features at the lunar terminator,
but it is noticeable. This may be due to the plossl eyepieces
used with this system, or it may be an artifact of the coatings
and complex optical system. The latter probably explains another
curiosity of this system. When a bright planet such as Jupiter
is displaced some one or two full fields’ of view width from
the eyepieces’ field of view, one sees the faint wide arc
of a large circle whose focus is the bright planet so displaced.
Finally, the telescope provides a very wide true
field of view (up to 1.7 degrees with a 53 AFOV degree 32mm plossl
when viewing occurs near the visual back). When used with a star
diagonal, the true field of view reduces to just over one degree.
Peformance (mechanical):
Focusing is accomplished by rotating the tube. Those
experienced at using a C-90 will find this scope easy to focus.
Some scopists may require adjusting the position of the eyepiece
in the diagonal cell. Again, to those familiar with such a focusing
style, this is not difficult.
The sweet-spot of best focus is very narrow. This
may be a necessary consequence of the optical design of this system
that allows a flat field with a very short focal length, or it
may be the necessary consequence of a modest amount of astigmatism.
If the latter is the case, it may be that in this unit fine focus
can be obtained, but at the cost of a bit more effort.
The field-flattening lens is very near the visual
back of the scope. So close in fact that one could easily crack
or scratch this lens by inserting a diagonal or eyepiece into
the screw on visual back. One solution, suggested by Mr. Palermiti,
is to shorten the insertion tube on the diagonal so that it does
not extend to the field-flattening lens.
The entire scope with the Orion Min-EQ tabletop
mount weighs in at less than 15 pounds. The OTA is slightly heavier
than the five-pound counter weight. In some positions, the counter
balance cannot withstand the force of the telescope weight. However,
it does not put undue strain on the equatorial locking screw.
Nor does it limit the effectiveness of the EQ-1M single axis drive.
The drive is very smooth and accurate. Once the scope is situated
relatively near the celestial pole, an object centered in a 4mm
orthoscopic eyepiece remains in that field of view without adjustment
two hours later. When the drive is turned on, images do not vibrate
and thus, do not impact the view of close double stars. (An addendum:
after three months of use, the RA axis has become a bit sloppy.
It seems to tighten up by rotating the axis a few times without
the scope or counterweight in place.)
By making a disk of wood 5/8 to ¾ inch thick
and a few inches in diameter with a notch at one end and placing
it on top of the cg4 tripod head, one is then able to dismantle
the screw-base of the Min-EQ and then mesh the rest of the Min-EQ
to the cg4 mount. Between the use of the Min-EQ tabletop mount
and the adapted cg4 mount, any object can be observed at a comfortable
height and location.
With the telescope’s relatively large true
field of view, an Orion Star Pointer provides an adequate means
for finding objects in the sky if one has a good familiarity with
the position of objects in relation to bright stars or has use
of a good star chart providing the same information. Another benefit
of the star pointer is that it is very light, hardly affecting
the balance of the equatorial mount. Further, the pointer has
an easy-to-use mechanism for adjusting its position. Finally,
the switch that turns the pointer on and off and adjusts the brightness
has a very definitive sound and feel. The only drawback of the
pointer is that one often leaves it on inadvertently. It would
be good if this unit had some type of automatic shutoff function.
The telescope comes with a screw on metallic dew
cap/light shade. Care needs to be taken when screwing on the dew
cap that the threads are not stripped. Also, in the dark especially,
but at any time, care needs to be taken not to let the cap slip
allowing its thread edge to touch the surface of the forward full
aperture lens. It is also possible to screw the full aperture
filters onto the telescope and then screw the due cap onto the
filter. Though there is no astronomical advantage to using full
aperture filters instead of ocular filters, one can disassemble
one of these filters and replace the glass with Baader filter
material, thus creating a very convenient solar filter.
The scope comes with a full aperture lens cap that
covers the front of the scope when the dew cap is not installed.
It would be a nice modification to the current Rubinar design
if this lens cap could be modified to fit on the scope with and
without the dew cap in place.
Peformance (composite/in the field):
Alan MacRobert is correct; a small telescope will
see more than a large telescope because it will get used more
often. This is due to the lack of excessive weight and clumsiness.
Further, a consideration for aging stargazers is exposure to the
cold. The lessened weight and size often eliminates the need for
assembling the scope outside or lessens the amount of time this
takes. These strengths are true of the Astro-Rubinar mounted on
the Mini-EQ1 mount. A second advantage of the low weight and lessened
size is the small amount of space that is needed for storage.
In the case of this particular scope; it, its mount and drive,
and all of its accessories stated above are stored in two 13”
plastic tool-boxes, the 15” soft padded bag, and Orion’s
smallest eyepiece case. These take up about two square feet of
shelf space, can be transported easily in any vehicle and can
all easily be carried outside in one trip.
History of this particular selection:
I was the owner of an MK-67 on a cg4 (mount/drive)
with a wide range of orthos and a stunning MK70 Konig (another
good suggestion by Bill and Mike). After two years of very satisfying
viewing with this assemblage, I began to grow dissatisfied because
my work, family obligations and age made me less and less willing
to set the scope up for viewing and take it down. Also, I missed
the terrestrial and near-focus views of the humble C-90.
Thus, began the journey of obtaining what I believe
to be the perfect balance in a telescope: good optical quality,
aesthetically pleasing, light weight, easy transport, easy assemblage
and dis-assemblage, robustness, good quality drive and tracking,
good near-focus capabilities, appropriate accessories.
To cover the cost of this purchase, I disposed of
the MK-67, MK-70, cg4. Many professionals and amateurs advised
me not to do it, because of the very good quality of the MK67.
Though the overall quality of the Astro-Rubinar does not stand
up to the standards of the MK-67, MK70, cg4 set up, it is better
suited to my tastes and needs.
An experienced amateur asked if I was disposing
of this in order to upgrade. With a slight bit of rye humor I
could honestly say that “No, I am downgrading.” Of course,
a downgrade to what I believe is more suitable for me.
After-the-Purchase Service:
My desire was to obtain a scope that provided the
ability to see objects only a few feet away and to see the Cassini
division on Saturn. Bill assured me that this scope, under proper
stability, could do just this because it was equal in optical
quality to the Questar 3.5. As I studied the advertisements, I
also noted the short focal length of 1000mm. This meant that I
could obtain a wide true field of view with long focal length
eyepieces. It also meant that University Optics 4mm orthoscopic
eyepiece would create a magnification in (what some consider the
ideal high magnification) range of 50 to 60X per inch. The advertisements
also showed that a 32mm plossl and a right angle 90 degree star
diagonal was included along with lens caps for the visual back
and the full aperture front.
Once the order was placed, I was told that delivery
would be in one to two weeks. Near the end of the two weeks I
called and learned that it would take somewhat longer. In the
third week, an email response to a further query informed me that
it should arrive soon. Soon it did; that very day. Bill, simply,
went ahead and had the scope shipped, from the Florida testing
site, by second day air, without requesting or requiring additional
payment.
Assemblage of all the obtained elements now in hand,
was a pleasure. Using it was a pleasure too, providing good views
and easily meeting my desire for a unit that was easy to handle
and provided a good near focus. It was also enjoyable to actually
have a certificate of optical quality. A further pleasant surprise
was the inclusion of three full aperture filters in very substantial
well-made housings at no cost.
Then, as always happens, imperfections became apparent:
scratches on the ring, chip in the field-flattening lens, a shockingly
long focal length with the diagonal in place resulting in the
realization that I should not have purchased a 4mm ortho for this
system as it now provided magnifications of 100X per inch of aperture,
the astigmatic and dissimilar intra/extra focal star and point
source light images, the dangerous nearness of the field-flattening
lens to the visual back and a 45 degree erect image diagonal being
provided instead of the advertised 90 degree diagonal (this was
fortunate for me in that I possess a very good 90 degree diagonal
but not an erect image diagonal). These occasioned a number of
calls and emails to Bill and Mike. Bill returned every email inquiry
quickly. Both Bill and Mike talked at length over the phone when
I called. Every query was responded to with full attentiveness
to the descriptions of my concerns. One such interchange was to
report the chip in the field-flattening lens, not so much to desire
a replacement (since it did not seem to affect performance) but
to put it on record in case it should enlarge through temperature
changes or mechanical stresses.
A sign of good customer service is the willingness
of a company to consider sensible suggestions. Bill was open to
my suggestions that the advertisement on the website be changed
to mention the focal length of the optical system with a star
diagonal in place and not just the focal length at the visual
back, and that the owner manual contain a warning that care was
needed in inserting the diagonal/eyepiece so as not to crack the
field-flattening lens.
Evaluating Oneself as an Observer:
The ITE optical evaluator, Mike Palermiti said to
me in a phone conversation that “Field "tests"
are not really tests of the telescope’s optical quality,
but, rather, a learning session for the observer. All too often,
amateurs spend too much time trying to evaluate an instrument,
when the facts are that they are really evaluating themselves
as observers.”
Novice scopists and amateur stargazers can see more
problems then might actually be present. We might overplay the
negative and underplay the positive. We may become a bit obsessive,
especially as it relates to systems-perfection. In this latter
regard, I am grateful to my tutelage under a number of persons.
These include the astronomer, Fr.Myron Effing (a student of Carl
Sagan’s) who taught me the advantage of the “brute force”
design; sacrificing cosmetics in order to put effort and money
into optical quality; Andrea Tasselli who once wrote that what’s
important about a telescope is that it is meant to be looked through
and only secondarily to be looked at, Bill Burnett who once questioned
my self-presumed ability to distinguish between a 1/6 and 1/8
wave-front corrected system based on lunar observations and Mike
Palermiti for his comments immediately above.
My mother-in-law who, in living that life common
to us all in which we learn to deal with accommodation, once said,
“You never get the whole pie. You have to work at accepting/liking/improving
the pieces you get.” Though my MK67 accustomed me to the
absence of astigmatism and a ribbon-like appearance to the Cassini
division; I am finding myself very satisfied with this telescope
which is very portable, stores easily, gives very good views of
terrestrial objects, performs as a long-distance microscope, gives
good astronomical views, whose drive and mount function flawlessly
and supported by two very knowledgeable and available professionals.
Addendum February, 2003
Since the original review I have made additional
discoveries about this fascinating telescope. Some of these are
elucidations of previous comments, and some are corrections.
These addenda are due to having had more use of the scope and
having, with the encouragement of Jeff Barbour and Mike Palermiti,
dissassembled the entire scope.
