Meade ETX 90 RA Review
Cosmology 101 Items',
I was browsing through a local Sam's store a few years ago when I saw the
ETX90-M below 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. I found that it was a variation of the ETX 90 RA model.
If you want one of these now, you can find them used on EBAY, but Meade has moved on from that simple and elegant telescope. You can still get something I think is comperable, as handy, and at a similar price. I'm thinking of the
Orion StarMax 90mm TableTop Telescope. No clock drive here, but great optics, super portability and simplicity, just the features I love about my ETX 90.
Another option is to get the
Celestron NexStar 90SLT Mak Computerized Telescope. It also is a 90mm
Maksutov telescope on motorized mount. This one has the Celestron SLT
altazimuth computerized mount, which operates much like the more modern
Meade ETX 90 version.
If it's an ETX you really want, you can go for the new computerized version,
like the Meade
Instruments ETX90 Observer Maksutov-Cassegrain Telescope. This version now as a standard uses a more
convenient altazimuth, computerized mount. The computer is necessary because in
altazimuth mode, both the vertical and horizontal axes must rotate to keep an
object in view, and the rotational rates vary with position. Thus, a computer
is necessary. Same fine telescope on an advanced mount, for less than the
original sold when introduced, even without the computer. You can get up to
speed on telescope mounts at Telescope Mounts.
When I examined my non-computerized ETX 90 purchase, 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 luxurious Rolex. But each
time I got the Questar impulse, I would remind myself of the other fine (and
larger) telescopes I could get for the money.
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 less extensive ensemble of features.
The sort version of this review is that I find the ETX optics to be of
absolutely top quality, and the mount adequate. The image below of the lunar
crater Copernicus was take with the ETX 90 RA, and demonstrates the optical
quality. The shortcomings can be inexpensively overcome if one desires. Newer
versions all have the same exemplary optics combined with computerized
Copernicus Crater through ETX 90
But I learned a lot about the ETX in my observational journeys. If you want
the long version of the review for more information, read on.
My ETX, shown above, 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, and a flip mirror with rear eyepiece/accessory port. It
also has slow motion controls on both axes.
The diagram above points out many of the features, including the
external view port, the RA adjustment knob and clamp, the DEC adjustment
control and clamp, the focus knob, and the flip-mirror control. Also
shown is the added slew control box, which gives fast and off controls that
allow positioning in the RA axis without introducing backlash.
The Questar, besides having all these mechanical features in far superior
quality, has in addition a control to flip an internal Barlow lens into
positon, a control that switches the view to the built in finder system,
and a back that can rotate left and right (from the image perspective) to
allow the eyepiece to be more comfortably positioned.
The ETX, being a simpler and less expensive piece of gear, has no internal
Barlow, a less handy drive system, and a small (barely useful) finder
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. Jupiter's cloud bands showed clearly, and it was noteworthy that
no color fringes were seen at the planets sharply defined limb.
First impression? The optics were superb.
When I tried the clock drive. I found a few things I didn't care for.
Disappointment one -- my big hands had trouble reaching in between the wide
fork supports to manipulate the RA adjustment and clutch knob. 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 not engaging or was slipping
I also found that the simple straight-through finder telescope was of little
value. It was difficult to get into a position to peer through the finder, and
it didn't focus well.
To troubleshoot the clock drive on the fork mounted ETX, I carefully removed
the base of the mount to see how the drive worked.
I found that the base was a very simple design. It also seemed different
than what I found described on some Meade ETX telescope websites. I've been
told that the design has changed over the years as Meade tried different
In any event, what I discovered on my ETX 90 model was a small motor with a
brass spur gear that engages a larger (3 inch diameter or so) plastic gear.
When the clutch knob is tightened, the large gear is unable to free wheel, and
thus drives the telescope.
A circuit board acts as a voltage regulator to maintain a constant voltage
on the DC clock drive motor for proper speed control.
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
As to the finder, after struggling to use the one provided on my ETX I began
to appreciate why Questar came up with their clever design. It's just very
difficult to find room for any kind of finder on such a compact telescope.
To solve my finder problem, I ordered the elbow-finder made 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. You can see the canted elbow finder in the above
To solve the problem of my clumsy big hands trying to work the RA controls,
I concocted an on/off/fast control. Wires run from the inside of the
fork mount base to a small hand-held control box (available from Radio Shack).
The control box is visiable at the bottom right of the above image. The
control box is attached to the telescope base with velcro when not in use. It
is detached when in use, and then hand-held.
On the control box is one toggle switch and two momentary push button
switches. The toggle switch is wired in series with the telescope's original
on/off switch. Thus it simply extends the on/off switch to be more readily
available than the original on the bottom of the base.
One of the momentary button switches is normally on, and is in series with
the on/off switch. When it is pushed, it interrupts power to the motor,
causing the Earth's rotation to allow an object to "catch up".
This procedure doesn't cause the backlash to reappear since the drive was
not mechanically disengaged.
The other momentary button is wired to allow power to bypass the regulating
portion of the circuit board, so it applies full battery power to the motor.
This causes the motor to run at about twice normal speed. The combination of
the two momentary switches gives a fast/slow slewing control to the RA axis.
With this hand-held controller, the telescope is now quite convenient to use,
and is one of my favorite instruments. I've been able to engage in some
astrophotography with the unit now that precise pointing and clock drive
control is available.
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. I must say that with all the plastic
used in the telescope's design, I was concerned that it would not hold up.
Now, years later, I can say that I've had no problems with my ETX 90 RA
Mars 2003 With ETX90
I've used the ETX-90 RA quite a bit now, and have compared it side by side
with my two Newtonians, 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
In general, the high resolution views through the ETX are quite
extraordinary. Images are very crisp, making the unit a fine lunar and
planetary performer. There is no noticeable color fringing, and the stubby
design of the telescope and mount delivers steady images. The above image of
Mars, taken through the ETX in 2003, is a good example of the quality of images
it provides. Check out the ETX
90 Astro Photos for more photo examples.
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 with my aging eyes.
Jupiter 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.
Star Observing with ETX 90
As to star observing, At first I didn't find this model of ETX all that
useful. The aperture is big enough to show all the Messier objects for example,
as well as hundreds of other objects. But with the combination of the rather
narrow field of the Maksutov optics and the awkward finder, locating star
objects is somewhat difficult. I'm sure the computerized versions help
considerably in making the ETX a better star telescope.
To address that problem, I developed a program for my HP calculator to aid
with finding stars and deep space objects telescopes that have setting
circles. The calculator can hold up to a few thousand object coordinates,
provides an easy alignment procedure, and presents a simple menu to select
objects for view. The program accounts for Earth rate, so once the RA axis ring
is set, it's good for the night (of course, some more expensive mounts have
motorized RA setting circles that do this compensation automatically).
Since the time of creating the calculator program, I've created a web page
utility that does the same thing, but with a superior interface. It's
named Star Pointer.
Star Pointer has the Messier, Caldwell, and Herschel 400 object catalogs
available, and the user can select any of the three. The program then
lists all of the visible (up) objects in any of the selected catalogs,
arranging them in azimuth order, starting in the Southwest. That way,
as one goes from object to object, minimal telescope movement is needed.
Star pointer can accomodate either Equatorial or Altazimuth mounts,
and displays, along with each object, its type, magnitude, and current
pointing coordinates. It updates the pointing coordinates about every
30 seconds. So once my telescope is aligned, I can just pick an object,
move to the indicated coordinates, and find the object of interest
either in the field of view, or exceedingly close by. The web utility can
also be handily used in the browser of a smart phone.
I've found that I can use this utility quite successfully with the ETX. By
aligning the polar mounted telescope with Polaris and doing the utility's
alignment procedure (which tells me where to set the RA axis) I find that the
ETX makes a very nice instrument for star observing. The setting circles are
plenty accurate for pointing the telescope.
With a 25mm Plossl eyepiece to aid in locating objects from the calculator
supplied coordinates, I find that most times the object I seek is within
the field at first glance. To increase my chances, I've found that using my
old 40mm MA Meade eyepiece works even better, as the view encompasses a larger
Now that I have a means of easily finding objects with the ETX, I can report
that it's a surprisingly good instrument for viewing many star objects. It's a
natural for double stars, and even most Messier and other objects show up very
well. The instrument, though modest in size, gives pin point images and offers
high contrast views, thanks to the telescope's internal baffling.
Since modifying the 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. The mount is still a
little idiosyncratic sometimes. I often find that after I mount the telescope
to the tripod wedge, I have to rotate the base to a position where the clock
drive isn't jerky. I have yet to resolve that problem, but I can work around
You can check out the pictures I've taken through the modified ETX at the
ETX photos page on this
Would I recommend the ETX 90 RA? With some reservations, yes. Optically it
is a wonder, but the clock drive setup needs some refinement to be useful.
That said, it is clear that I'd recommend the newer models, like the Meade
Instruments ETX90 Observer Maksutov-Cassegrain Telescope.
The newer ETX 90 models solved my main complaints in an even more grand
fashion by including drive motors on both axes and a computerized driving
system. If your interest is a portable instrument to augment your equipment
arsenal, I think you'd find the ETX90 a great supplement. If you don't want the
computerized model, then keep your eyes on Ebay for an RA model and get a
telescope with superb optics for a bargain.