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The Purchase
I was browsing through a local Sam's store a few years ago when I saw an
ETX90-M on sale for $250. I was flabbergasted. It didn't seem that long before
when the ETX-90 had been selling for more like $500.
That time frame was before the computerized ETX models, and only the RA axis
was motorized. I didn't know what an M model was, but I decided that for $250 I
was willing to find out.
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I was happy to see that the ETX had many of the features of the venerable
Questar, a telescope I'd ogled over almost annually, but never found the cash
to purchase. Of course, for the money, the Questar is a much finer piece of
equipment. Sort of like comparing a Timex, a perfectly adequate watch, with a
Rolex.
None-the-less, Meade advertised that the ETX had precision optics equal to
any telescope on the market. The incredible price was due to the heavy duty
plastic construction on the ETX mount rather than the polished aluminum of the
Questar, and a more limited ensemble of features.
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The sort version of this review is that I find the ETX optics to be of
absolutely top quality, and the mount adequate. Newer versions all have the same exemplary optics combined with computerized
mounts.
If you want the long version of the review, read on.
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The Features
My ETX shares in common with the Questar a 3.5 inch Maksutov optical system,
a clock drive on the RA axis, a fork mount with accessory table-top tripod
legs, a flip mirror, and two eyepiece ports. It also has slow motion controls on
both axes.
The Questar has in addition to all of this a built-in barlow lens, an
eyepiece fixture that rotates for convenient viewing, and an
ultra-handy finder system that uses the same eyepiece as the main telescope.
The ETX, being a simpler and less expensive piece of gear, has no internal
barlow, a less hardy and less accurate drive system, and has a small (barely
useful) finder telescope.
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On the first evening that I had the ETX, I set it up and peered at Jupiter
and the Galilean moons. I was pleasantly surprised to see the moons appear as
perfectly defined tiny discs. I'd never seen the moons so well defined, having
viewed them generally with Newtonians, which always added a few spikes around
the moons.
First impression? The optics were superb.
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The Problems
When I tried the clock drive. I found a few things I didn't care for.
Disappointment one -- my big hands could hardly reach in between the wide
fork supports to manipulate the RA adjustment and clutch knobs. The
fork supports are much thicker than the trim aluminum ones of the Questar, and
being plastic must be so to have the necessary strength.
Disappointment two - After only a few minutes of passable tracking, the
clock drive seemed not to be working at all.
I scoured the manual and rechecked my procedures, and was left with only one
conclusion, the clock drive was not working properly. The clock motor was
either not running, or some component was slipping badly.
I'm an impatient sort. I didn't particularly want to send the unit back,
having never really gotten to use it. I was afraid it would take weeks or
months to get it back. I did spend a day trying to call the Meade tech support,
but I was never able to get through.
So I decided to carefully dismantle the base and see what might be going on
with the clock drive.
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I found that the base was a very simple design. It also seemed different than
what I found described on some ETX websites. I've never been able to resolve
whether there had been a design change over the years, or if the M model used
a simpler and cheaper design to obtain the cheaper price.
In any event, what I discovered was a small motor with a brass spur gear
that engaged a larger (3 inch diameter or so) plastic gear. When the clutch
knob was tightened, the large gear was unable to free wheel, and thus drove the
telescope.
A circuit board acted as a voltage regulator to maintain a constant voltage
on the motor for proper speed control.
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The Solutions
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Upon examination, I found that the
motor in my unit worked properly, but the spur gear was slipping on the motor
shaft. A drop of epoxy solved the problem nicely.
I found the tiny straight-through finder to be of little value. I can see
why Meade went to the computerized control and why Questar designed their
clever finder system. There just isn't room on such a compact telescope for a
conventional finder.
I ordered an elbow-finder made at the time for the ETX-125, and it has
worked better. It is still a bit clumsy in that the eyepiece of the
elbow-finder gets in the way of viewing through the telescope eyepiece.
One ETX owner suggested turning the elbow-finder so that the eyepiece
sat about 45 degrees from the telescope eyepiece. I followed that advice
and it reduced the interference problem.
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To solve the problem of my clumsy big hands trying to work the RA controls,
I concocted an on/off/fast control ran by push-button switches. I found that I
could modify the circuit board by adding a switch to interrupt power for a
remote on/off, and could use another switch to bypass part of the circuitry to
cause the entire voltage of the batteries to run the motor at a faster rate
(slew). With this hand-held controller, the telescope is now quite convenient
to use, and is one of my favorite instruments.
The computerized designs now used by Meade actually attack both of my
trouble points, so I would have to say that I'd not hesitate to buy one of the
newer units -- if my old one ever breaks.
The Views
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I've used the ETX-90M quite a bit now, and have compared it side by side
with my two Netwonians, a 6 inch f/10 DOB and a 6 inch f/5 equatorial. I still
enjoy setting up all of the scopes and comparing views of planets and the
moon.
In general, the views through the ETX are quite extraordinary. Images are
very crisp, making the unit a fine lunar and planetary performer.
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I generally view through the ETX at about 150 power, but on good nights on
bright objects I can get to 200x. I can see the large-scale features on Mars,
and of course the polar caps.
On Saturn, I can see the lighter color of the equatorial band, and can
clearly see the Cassini division of the rings. I can see about 4 of Saturn's
moons as tiny points of light.
On Jupiter I can see the dark bands nearest the equator, and an additional
dark band in the Northern hemisphere. The Great Red Spot is visible as a light
colored feature. I cannot really see color on Jupiter, it appears as a black
and white image.
The moon is a wonderful object with the ETX, especially with the fabricated
hand-held controller. With a twist of the elevation control I can move up and
down along the moon's terminator, and with the push of a button, slew left and
right. Trolling around on the moon is a delight.
When comparing the ETX with the 6 inch telescopes, the ETX holds its own. On
most nights, little more detail is seen on a planet or the moon with the bigger
telescopes than with the ETX. But on good nights, as you would expect, the
bigger telescopes will show more detail.
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As to star observing, I don't find this model of ETX all that useful. The
aperture is big enough to show some things well, but the combination of the
rather narrow field of the Maksutov optics and the awkward finder, locating
star objects is just too difficult. I'm sure the computerized versions help
considerably in making the ETX a better star telescope.
Since the unit has a clock drive, I've tried a bit of photography through
it. The drive isn't good enough for long term time exposures of star objects,
but has worked well for photographing the moon and planets. I don't think even
that would have been possible without the hand-held controller I added.
You can check out the pictures I've taken through the modified ETX at the
ETX photos page on this
site.
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Recommendations
Would I recommend the ETX90-M? Not as it was when I first purchased it, but
with the refinements -- yes. That said, it is clear that I'd recommend
the newer models in that they've solved my main complaints in an even more
grand fashion.
Where do you get one? You can check out eBay
Stores  . Lots of people buy the ETX because it's do darned
cute. But if they aren't into astronomy, it isn't long before they decide to
let it go. And you can always take advantage of another person's aperture
fever.
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