After joining an enjoyable astronomy egroup that was devoted to the use of
small, refractor telescopes, I was quickly enthralled with the group. The views
through 60mm telescopes, described by many of the most experienced members,
really caught my attention. Was what they described possible?
The problem was, I didn't have a telescope that fit their mainstream
emphasis. My only refractor was a 50mm Jaegers
Refractor, and I was admittedly amazed at how well it presented those
targets. But I'd never used that telescope for star objects. I was thrilled
when a member graciously donated an abandoned, vintage 60mm Monolux of 700mm
focal length (f/11.7) to my cause, so that I could use precisely the size
instrument that was causing all the buzz..
The telescope in received condition
As you can see in the image to the right, the old
Japanese made instrument had seen a number of years and showed some wear. But
the Monolux is considered a good representative of the many Japanese telescope
sold in the heyday of small refractor telescopes. Based on that I wanted to
give it a fair tryout.
Visible in this image are a few scrapes and scratches, and a couple of holes
that were likely used at one time to mount a finder scope. You might also
notice that the focuser is of the 0.965 inch variety. It still worked well, but
had only about a 2.5 inch travel, and of course only accepted the small 0.965
inch eyepieces.
Here's another view of the telescope as received. Incidentally, the tripod
was not part of the donation, only the telescope. Again, you can see a few
unused holes in the body of the telescope.
Here you get a better view of the focuser assembly. The holes in the side of
the tube were likely used to mount the telescope to its original mount. The
telescope's original mount was long gone, but that's not likely a great loss.
Refractor telescopes even in the era of this model were still notorious for
having mounts that were undersized -- with the exception of a few, like
the venerable Unitron.
I cover a few of details of my efforts to achieve good performance with the
telescope because the obstacles I encountered are likely typical of those you
might experience should you decide to refurbish a vintage refractor
telescope.
First, when I got the telescope, I had but one 0.965 inch eyepiece to use in
the instrument. So I purchased a hybrid diagonal that allowed me to use my 1.25
inch eyepieces. The hybrid diagonal has a 0.965 inch snout on the telescope end
so that it will slide into a 0.965 focuser. On the eyepiece end it has a full
1.25 inch adaptor.
This provided a workable solution for using most of my 1.25 inch eyepieces,
but there were a couple of limitations. Since the focuser didn't have a locking
screw to hold the eyepiece or diagonal, the heavier 1.25 inch eyepieces would
cause the star diagonal to rotate under their weight. I had to be sure the
eyepieces were placed in a perfectly up position. Second, the limited
2.5 inch travel of the focuser didn't let me get full use of my Barlow. I
could use it on some eyepieces, but not others.
To use the telescope, the first thing I had to do was rig up a mounting.
Fortunately that problem was already mostly solved. I just had to drill a 1/4
inch hole in a 3 inch hose clamp, and use the clamp to fasten the Monolux to my
pipe fitting tripod. A
1/4 inch screw of 2 inch length goes through the hose clamp and through the
mounting board fastened to the pipe fitting tripod. This simple method
provides a telescope mount of exceptional stability and ease of use.
My first light experience was a bit disappointing. When I looked at Saturn,
I was unable to focus to a nice, crisp image. I could see that it was the
planet Saturn for sure, but the image was definitely sub-par. I pointed the
telescope over to a moderately bright star to check out the in and out of focus
star images.
On one side of focus the star image looked reasonable normal (a bit oval),
but on the other side of focus the pattern was terribly distorted. Something
was clearly wrong. Was the telescope a dud?
At the suggestion of a member of the aforementioned astronomy egroup, I
examined the telescope's objective. It is an air-spaced doublet. After trying
all combinations of arrangement of the two elements, I determined that as
received, the front element had in the past been removed and accidentally
reversed when replaced.
After correcting that discovered anomaly, I tried for another chance at a
first impression. Images were much better. At low to moderate power the star
images looked fine. But at power in the 100x range, images were still
not quite as good as I'd hoped. Another glimpse at a star image revealed a
noticeable amount of astigmatism.
Astigmatism is characterized by oval shaped out of focus star images, with
the inside-of-focus oval at 90 degrees to the outside-of-focus oval. By
rotating the eyepiece and finding that the pattern stayed in the same
configuration, I was able to confirm that the astigmatism was coming from the
telescope's objective, not the eyepiece. Had the eyepiece been the trouble, the
orientation of the oval patterns would have rotated as I rotated the
eyepiece.
On another tip from an egroup member I spent a day meticulously rotating the
objective elements with respect to one another. After each adjustment, I would
re-test the out of focus images by looking at a pseudo star image. My pseudo
star image was the sun's reflection off of a power transform insulator some 1/4
of a mile away. The curved surface of the insulator gave a reflection that
proved a worthy fake star. I was amazed that this technique worked, and by
following the procedure carefully I was able to find an arrangement of the
objective elements that virtually removed the astigmatism.
Eureka!
More actual astronomical target observations through the telescope confirmed
that it was performing well. Planetary images were crisp and tolerated
magnifications of up to 150x. Moon images were very pleasing. The telescope was
also able to split some tight double stars near it's theoretical limit. Note
that the 150x is more that any report as the maximum usable magnification of
120x for this sized instrument.
The 120x maximum that you often read is obtained by applying the general
rule of maximum useful magnification as 50 times the objective diameter in
inches. Thus, 2.4 x 50 = 120. However, atmospheric turbulence is one of the
contributers to this general rule, and small aperture refractors are less
affected by atmospheric turbulence than larger instruments. It's not uncommon
for quality 2.4 inch (60 mm) refractors to achieve up to 75 times per inch of
objective diameter. For a 2.4 inch, that means up to 180x when seeing is
exceptional.
It was time to move forward.
The Decision To Refurbish
Now that I knew the Monolux had good optics, I decided to go the distance
and refurbish the vintage refractor. To start, I went after all those old,
unused holes. I filled them with epoxy, and after the epoxy dried I sanded it
down to the point of being unnoticeable.
Next I removed the focuser and the objective cell and repainted the inside
of the telescope tube with flat black paint. The original black coating was a
bit thin in places, and with only 60mm of aperture to work with I didn't need
any interference from stray light sources.
Next I sanded and repainted the telescope's outside. Showing no imagination
at all, I painted it white. After about 3 coats of paint, the telescope tube
looked good as new.
I then added a 6x30 finder scope. I decided to not re-install the original
focuser. Instead, I purchased a quality 60mm focuser from Meridian Telescopes. The focuser
is a heavy duty focuser of metal construction with a 6 inch travel, and accepts
standard 1.25 inch diameter eyepieces. Since the position of the eyepiece with
standard 1.25 inch star diagonal was further away from the objective than with
the original focuser, I had to shorten the main tube by the difference. When I
finished installing the focuser, I re-attached the objective cell, stepped back
and admired a fully refurbished, vintage 60mm Japanese refractor.
At left you see a closeup of the refurbished telescope. No more scratches
and unused holes. You can see the new focuser in this image, and the new finder
scope. The telescope is shown mounted to my good old pipe fitting tripod. The
pipe fitting tripod is easy to use, and makes a super steady mount for my
new old telescope.
The mount, as shown on the pipe fitting tripod page
serves multiple duty. A single wing-nutted bolt is all that must be removed to
switch to either my 50mm Jaegers refractor, or my newly completed 60mm f/16.7
Carton refractor. By switching tripod heads, I can also use the tripod to hold
my ETX90 when I'm in a Maksutov mood.
The Views
I've had a chance to do a little viewing through the 60mm Monolux since
the final optics alignment and the refurbishment. Starting with the moon,
I've been startled by the clarity. I can routinely use magnifications up
between 100x and 150x. Comparing it to a formerly owned Meade 90mm refractor
(a Chinese import), I'd have to say that the image quality in the Monolux
is better and the images crisper.
I've looked at Jupiter on a number of occasions. I could easily see the two
major belts on Jupiter, and see that the Southern belt is split into two
narrower belts. I could make out darker splotches along the Northern belt. I
was not able to resolve the Great Red Spot this time around, and I understand
that it's been a rather low contrast object. I was, however, able to spot Io's
shadow as it shuffled across the planet. The shadow was very tiny, and not
always visible, but I could make it out most of the time.
Update. In 2010 the Southern Equatorial Belt on Jupiter seemed to
disappear. This strange phenomenon has occurred before, though not often.
Because of the missing SEB, I was able to detect the Great Red Spot for the
first time with my Monolux 60mm telescope. When the SEB is visible, it merges
with the Great Red Spot, making it to difficult a target with the Monolux.
I haven't looked at many DSO targets yet. I've seen the Andromeda galaxy
(M31) and one of its companions (M32), the Ring Nebula (M57), the Pleiades
(M45), and the double cluster in Perseus. The Orion nebula is a wonderful
target, and the 4 brightest stars of the Trapezium are visible through this
60mm. I was able to just glimpse the Crab Nebula (M1) from my backyard
observing site. This is just a tiny fraction of the objects within the grasp of
this size telescope, and I list these few as just examples of what such a small
telescope can do.
The Monolux does a very nice job on double stars. Star images are always
crisp, and at moderate power at most a single, dim ring is seen around the
brighter stars. Contrast that with my ETX90, which while having excellent
optics, always gives couple of shimmering rings around even moderately bright
stars. The central obstruction of the ETX90 Maksutov optics causes the brighter
diffraction rings. While the ETX90, with its greater aperture, can split closer
doubles, the view is not as pleasing as through the Monolux refractor.
With its light weight and low-maintenance, solid construction, the
Monolux is a great telescope for those impromptu or short evening
tours of the universe. Since most of my observing sessions fall into that
category, my Monolux and Carton 60mm telescopes get quite a bit of duty.
Summary and Final Thoughts
The reputation of the poor 60mm refractor has taken a beating during the
last several years. Such telescopes used to be considered not only fine
beginner telescopes, but good supplements to any amateur astronomer's
collection. Just look at what a 60mm Unitron goes for now-a-days, if
you can find one for sale.
Now, most 60mm refractors are Chinese imports, made to inexpensive standards
with lots of plastic, and sold by most distributors as telescopes for kids.
They come with ultra-cheesy mounts and poor quality eyepieces. No wonder they
don't inspire many youngsters to become astronomers.
But if you want a lot of fun and a bit of a challenge, find an
abandoned vintage telescope at a garage sale or on eBay. There are a number of
brands you'd be safe with. The following list is not exhaustive, and with a bit
of research you can learn of other brands: Tasco (yes, the old ones were good),
Towa, Sears, Monolux, Edmund, Unitron, and Jaegers.
If you observe with a small telescope, or even a large telescope, I invite
you to the Amateur
Astronmer Survey page to contribute to the survey. See how your use of
telescopes and target interests line up with other observers.
