Meade ETX-90EC Telescope
- Optical Diameter: 90 mm
- Max Useful Magnification: x 325
- Finderscope: Optical
- Mount Type: Altazimuth
- Focal Length: 1250 mm
- Optical Design: Catadioptrics
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ETX-90EC has good optics, but a flawed mount
Pros
Small, light, good optics.
Cons
shaky mount
Recommended it?
No
The Bottom Line:
I recommend this telescope for those doing casual astronomical viewing of bright objects, and terrestial viewing. The mount is too shaky for serious use.
The ETX-90EC is a good little telescope for non-critical astronomical viewing. It has diffraction-limited optics, a compact size, light weight and a sophisticated mount with alta-azimuth and equatorial capabilities, and an optional go-to computer controller. If you are looking for a small telescope for casual viewing, you will be satisfied. The go-to mount makes it possible to find dim objects in a light-polluted sky where there is a dearth of guide stars. Once again, for serious viewing you need a dark sky, where the guide stars are naked-eye-visible, with the ETX-90's go-to computer, you need only two bright guide stars to setup the computer, then you can slew around the sky and view deep sky objects.
I think the problems with the ETX-90EC are at the root of trying to put too much into a low cost telescope. I will enumerate the problems that limit this telescope below:
1. The mount is poorly made. There is a lot of backlash in the gearing of the drives, and a lot of vibration in the drive. The stepping motors couple with the mount to cause vibration in the image as long as they run. This is most noticeable at high magnification planetary viewing.
2. The weak mount makes this telescope largely useless as a photographic platform. The long, f13 focal length also makes it pretty poor, but bright objects should be photo-able, except the mount will fight you at every turn as you try to focus and control the camera.
3. The mount is too short for equatorial operation. Polar alignment is nearly impossible because the guide scope is nearly recessed behind the base of the telescope. A right-angle guide scope would help. You can't reach the focusing screw at high latitudes because it is recessed behind the base of the mount. I use a clothespin to adjust the focus. It also helps with the vibration. Did I mention that I don't like the mount?
4. The small aperture, coupled with long focal length gives dim views of DSOs. This is not a cope for viewing anything dim. You will see very fuzzy, indistinct, black-and-white views of those glorious photos they use in the ad-copy. At least this limitation is obvious to anyone who knows what a 3.5 inch, f13 telescope can show. Its not a quality problem, just built-in to the physics.
5. The go-to computer works only mediocre. I think this is another mount problem. There is so much backlash in the gearing, that even after the computer "learns" the gearing, the telescope doesn't place objects within the guide scope reliably. A set of 10X50 or similar binoculars can be mounted on top of the OTA to act as a much better guide scope, because of its wide angle view. In fact, this gives you a go-to binocular, worth a lot in itself.
In summary, the 3.5 inch Maksutov-Cassegrain is a good little design. We all know about the Questar, and how great it is. Meade copied a lot of good things from them, but the mount isn't one of them. Its a shaky design, which really limits the telescope. If you know about this ahead of time, you can make an informed buying decision.
I think the problems with the ETX-90EC are at the root of trying to put too much into a low cost telescope. I will enumerate the problems that limit this telescope below:
1. The mount is poorly made. There is a lot of backlash in the gearing of the drives, and a lot of vibration in the drive. The stepping motors couple with the mount to cause vibration in the image as long as they run. This is most noticeable at high magnification planetary viewing.
2. The weak mount makes this telescope largely useless as a photographic platform. The long, f13 focal length also makes it pretty poor, but bright objects should be photo-able, except the mount will fight you at every turn as you try to focus and control the camera.
3. The mount is too short for equatorial operation. Polar alignment is nearly impossible because the guide scope is nearly recessed behind the base of the telescope. A right-angle guide scope would help. You can't reach the focusing screw at high latitudes because it is recessed behind the base of the mount. I use a clothespin to adjust the focus. It also helps with the vibration. Did I mention that I don't like the mount?
4. The small aperture, coupled with long focal length gives dim views of DSOs. This is not a cope for viewing anything dim. You will see very fuzzy, indistinct, black-and-white views of those glorious photos they use in the ad-copy. At least this limitation is obvious to anyone who knows what a 3.5 inch, f13 telescope can show. Its not a quality problem, just built-in to the physics.
5. The go-to computer works only mediocre. I think this is another mount problem. There is so much backlash in the gearing, that even after the computer "learns" the gearing, the telescope doesn't place objects within the guide scope reliably. A set of 10X50 or similar binoculars can be mounted on top of the OTA to act as a much better guide scope, because of its wide angle view. In fact, this gives you a go-to binocular, worth a lot in itself.
In summary, the 3.5 inch Maksutov-Cassegrain is a good little design. We all know about the Questar, and how great it is. Meade copied a lot of good things from them, but the mount isn't one of them. Its a shaky design, which really limits the telescope. If you know about this ahead of time, you can make an informed buying decision.
