An ETX-125, C5+ and a MN56 (A brief planetary comparison)

I initially posted this article to the Astrofieds Observing message boards in August, 2001. Over time I've received emails from folks suggesting I expand some sections and post it to Cloudy Nights. What follows is the core of the original post with several new sections. The reader should be aware that I've replaced all three telescopes in this article with (1) Meade 7" lx50. The lx50 fills the role of my small telescope and handily beats all three mentioned telescopes on the planets.

Over the past several weeks I've fallen into the habit of rising early (3:30 AM) and observing the planets. The early morning hours provide me the steadiest skies my part of the country supports. Evening observing hours are plagued by falling temperatures causing currents both in the air and in my telescopes as the optics cool. In fact, the period right before and after dawn are tremendous windows of opportunity for high power observing. The air becomes dead still and I find my ceiling of magnification jumping another 20%. On such occassions I'm able to observe Saturn at 500x with my 12.5" Portaball and watch it fill the entire FOV as I search for the elusive Encke Gap (I've yet to see it - maybe next year).

I'm also more observant in the early hours as I'm refreshed from a good nights sleep. Many nighttime observing sessions are cut short by fatigue. You see I'm a morning person by nature.

What follows is a loose, subjective and quick report of a single morning, a single object and three telescopes. I encourage you to not vest too much creditability in what follows. Rather, view this article as a single data point in your telescope research efforts. Since this was originally posted as a semi-observing report, it lacks many of the controls a formal review would contain.

Since we were experiencing a heat wave, I wasn't surprised to step outside and find it 70 degrees during these wee morning hours. No wind was present and the air felt still. Glancing back into my garage I saw a C5+, an ETX 125 and a MN56 (5" Mak-Newt) all setup and waiting to be used. Which would it be? Feeling a burst of energy I made the decision to pull out all three and train them on Saturn

Looking up I noted an overcast sky with only the planets, brightest stars and a waning moon shining through. Unlike most other astronomical objects, a thin haze of clouds doesn't adversely affect the view of the planets. Many times such a haze is a sign that seeing conditions are good. Taking this as a good sign I glanced around and found Saturn still low in the sky, roughly 30-degrees. Jupiter was just visible above my tree lined horizon and far too low to be of any interest. Obviously, as the planets get higher the views will improve over what I'm reporting.

I used Radian eyepieces for all three telescopes. I used a GTO Barlow on the MN56 as it's an f/6 instrument and my highest power Radian is 8mm (100x on the Mak-newt).

First up was the C5+. Using the 10mm Radian (125x) I was able to see the Cassinini division but no discernible detail in the rings outside of the A and B ring. Saturn itself showed only a hint of shading on the surface. Using the 8mm Radian (156x) gave a larger image but no further detail. The boundary between the rings and space did not have a tight border and I suspected scatter as the culprit. Even so, the image was good and would please most people.

The C5+ uses a single fork arm assembly mounted on a sturdy tripod. I like the single fork arm assembly as it allows me to rotate the diagonal out of the way of the fork arm when pointed near the zenith. A dual fork arm telescope is limited in this respect and problems arise as you attempt to use the focus knob. Unlike others, I didn't find any vibration or sturdiness problems in using a single fork arm with the 5" sct. Damp time is roughly 2 seconds and reasonable in my book.

Next up, the ETX-125. With the 14mm Radian (135x) I quickly noted the a crisper image in the ETX. The Cassini division stood out starkly and I detected some detail within the rings themselves. Putting in the 12mm Radian (158x) shading became apparent on the planets surface. This took the shape of banding around the planets body. Contrast was definitely higher with the ETX-125 and the boundary between the rings and space beyond it was very stark. In fact, one area in which the ETX-125 beats both the C5+ and the MN56 is in the pure starkness of these boundary areas.

The dual fork arms of the ETX-125 hampers use of the focuser when viewing near zenith and here the C5+ with the single fork arm is superior. Additionally, the damp time when focusing is roughly 4 seconds in length. Several manufacturers have stepped forward and sell devices to fix this. Meade and JMI sell motorized focusers which are controlled from the hand controller. Scopetronics sells a long focuser knob attachment. Either way, prospective buyers should be aware that they will need one of the aforementioned aftermarket products.

Finally, the MN56s turn. Using the 8mm Radian (93x) the first thing I noticed was a slight yellow hue to the planet. Quickly switching back to the ETX-125 I found the view of Saturn stark white. My intention is not to over emphasis this slight warm tinge, it simply surprised me and I wonder what would cause this? The MN56 showed the Cassinini division easily and the detail in the rings that I glimpsed in the ETX-125 was more pronounced. I quickly barlowed the Radian 10mm (150x) and the slight shading I noticed on the planets surface in the ETX-125 also became more pronounced.

The MN56 is a 10 lb tube which I mounted on a simple CG5 mount. With the legs fully retracted, the eyepiece is at a comfortable height for viewing while seated on my modified piano stool. Damp time is roughly 2 seconds. I never purchased an RA drive for the CG5 as the slow motion controls worked just fine to track targets up to 200x. Since I never used the MN56 over 200x this never became an issue. Using the 50x/inch rule for maximum magnification, 250x would be tops anyway.

It's obvious that the MN56 performed the best of all three telescopes on Saturn. Low contrast detail that was faint in the ETX-125 became much more apparent in the MN56. Likewise, low-contrast detail that eluded the C5+ was apparent in the ETX-125. However, muddling the waters a bit is the superior contrast of the ETX-125 on boundary areas (limb of the planet). My guess is the ETX-125 has superior baffling to either the MN56 or the C5+.

I regret having sold all three telescopes as I feel further comparisons across a broad spectrum of targets would be helpful. While the outcome of this comparison was clear, on other objects things would tilt the other direction. For example, on low power wide field objects the ETX-125 would lose. On absolute portablilty, the MN56 would trail behind. I can't over emphasis the need to evaluate each authors contribution as a single data point, not the whole picture.

One last comment on the C5+. While it trailed behind the other two on optical performance of a single target on a single day, I feel it wins on build and mechanical excellence. The C5+ is built from actual metal parts with only a little plastic here and there. The optical tube can be removed from the fork arms with the single twist of a thumb screw allowing one to use it as a spotting scope on a tripod. It is marvelously built and my favorite SCT after owning a 5", 8", 10", 11" and briefly a 14" SCT. It is truly a shame that the C5+ is no longer produced.