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Review of the Meade ETX 90 RA Maksutov

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Meade ETX 90 RA Review



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. 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 mounts.

Copernicus Crater w/ETX
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.



The Features

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 telescope.

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.



The Problems

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 badly.

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.



The Solutions

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 schemes.

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 nicely.

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.

ETX 90 Elbo Finder

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 image.

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 holding up.





The Views

Mars through ETX 90
Mars 2003 With ETX90
More Photos

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 moon.

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).

Star Pointer

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 area.

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 it.

You can check out the pictures I've taken through the modified ETX at the ETX photos page on this site.



Recommendations

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.