Meade ETX90-RA


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Brand and Model:Meade ETX90-RA
Price ($USD):$180
Type:Maksutov-Cassegrain
Attributes: un-checked Go-To un-checked PEC
Aperture:90mm
f Ratio:13.8
Focal Length:1250mm
Finder:8X21
Electric Power:RA drive
Mount:fork
Tripod:table top legs
Weight (lbs):8
Dimensions (w/h/d):15X8X9
Description:See http://www.meade.com/catalog/etx/etx_mak.html

Vote Highlights Vote
Meade ETX90-RA
First the bad news. It's easy to get sucked in by the oh so cute appearance of this thing. But ergonomically, it has to be about the worst design around. For me, the easiest way (or least difficult, I should say) to use it is to set it on the ground and lay down sideways behind it. For comparison, the Orion shorttube 80 on the tabletop equatorial mount is a cinch to use just about anywhere.

Besides having a pitiful 21mm aperture, the finder scope on the 90RA is straight through, not right angle; so I must scoot up underneath it -- a lot like I am fixing to change the oil on the car -- to look up through it (recall, we're laying on the ground here). And since this is an 8 X 21 finder, you don't get near the field of view or light gathering that you would get on an 8 or 9 X 50 finder. But, it's good enough to find Saturn, Jupiter, the moon, or M42. However, given that the scope itself has a 1250mm, f13.8, focal length -- which ain't going to give you much of a field of view -- if you were figuring on scanning around to find things, you might want to do a little more figuring. Scan around with the shorttube 80? Sure! Scan around with the 90RA? Well .... hmmmmm. Actually, the shorttube 80 with a 32mm eyepiece essentially IS a finder scope; so I usually don't bother putting a finder on the shorttube 80.

Again, comparing the 90RA and the shorttube 80: The mostly plastic base of the 90RA makes for a real case of shivers and shakes every time you touch the focuser or any other knob. The tabletop equatorial mount with the shorttube 80 is reasonably steady.

The 90RA drive takes three AA cells. I use NiMH without any problems. But, you have to remove three screws to remove the base to install and remove the AA cells. As long as we indulging in bad physical design, let's go whole hog eh? Now, here the shorttube 80 isn't much better: You must take apart the shorttube 80's drive to install a 9V battery (again a NiMH in my case), and in some positions, the counter weight on the tabletop equatorial mount bumps into the drive motor; so you have to move the weight out to a position that unbalances things.

The location of the RA and DEC manual adjustment knobs on the 90RA is such that it is a bit inconvenient to get to them when your head is blocking access to them because you are doing something stupid like looking in the eyepiece.

There are a number of dimwitted physical design details on the 90RA, and that is the reason for my rather low ease of use rating.

Now for the good news (Yes, there is some good news!).

After you get past all the aggravations and annoyances, the optics are pretty good. I would say they support magnifications at or near the 50X per inch Nirvana goal. I can't say you'll be blown away by any exquisite detail, but they ain't bad. Comparing it to my shorttube 80, I would have to give the 90RA a slight edge on detail. And, of course, the 90RA has absolutely no purple halo (which is in abundance on the shorttube 80) on anything. Now, let's be clear about this. When it comes to detailed views of something like Saturn, my Orion f8 6-inch dob, and Meade 8-inch UHTC LX10 will both trounce the 90RA into the ground, dig it back up, trounce it back into the ground, dig it back up, and then throw into a dumpster and spit on it. The 90RA offers decent, but not outstanding, 90mm planetary views and nothing more. This scope isn't about to put Televue out of business any time soon. It's use on deep space objects is very limited (as is the case for most non-premium 90mm scopes). You might be able to grab a few open clusters, but I wouldn't count on much of anything else.

The 90RA does provide a simple, but actually quite accurate way to set the angle for polar alignment. After I have it polar aligned, mine does a good job of tracking. So give it pat on the back for that. The RA setting circle is big enough to be semi-useful. The DEC setting circle might get you into the general neighborhood, but will probably leave you to do some groping around after that.

I know I have razzed the 90RA a wee bit here, but I actually do give mine some use. I got mine for $149 with the 26mm deluxe Plossl eyepiece when Meade (via Astronomics) was running a special on these things. For the money, it's good value. It's main strength is that it is very convenient to pick up and take outside for casual planetary use. After you get used to the boneheaded physical design (assuming you do get used to it), the optics deliver good enough performance to fix you up for those times when you don't need the ultimate in exquisite planetary views.

And you do have to admit ... These things are soooooo cute.

Overall Rating: 6
Optics:7 Mount:5 Ease of Use:4 Value:9
Weight: 16 (Trustworthy Vote)
Date:
By: percy_smogg
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=348878


Meade ETX90-RA
An ETX90-RA Review

Overall Review: Delightful and fun. Very good planetary performance. Great near focus (microscopic) performance. Good terrestrial views, only limited by narrow field of view (FOV). Some limitations on deep sky (nebulae). Mechanically functional, even charming, for the experienced stargazer. The inexperienced scopist may find the mechanical functionality of the ETX discouraging in a manner similar to the ubiquitous department store altazimuth mounted 60mm refractor.

Equipment Reviewed
- ETX90-RA; second hand but in unused or nearly unused condition
- ETX90 Hardcase (Meade #774), second hand, used, functional, no keys
- 8X25 right angle finder (Meade #884), new
- Scopetronix Visual Back, new
- EZ-Focus cord, new
Cost (including shipping and with equivalent accessories)
- As described, $330
- Retail RA model* ($380-$400) *limited retail availability
- Retail EC/AT model ($700-$800)

Comparative Reviews:
- to a 100mm (F15) diffraction limited Rubinar on a table top equatorial mount
n the ETX90 has a slight optical superiority (contrast, detail, near focus)
n the ETX & Rubinar are equal on chromatic correction, FOV,cool down
n the Rubinar is superior for photographic use (flat field)
n the ETX is mechanically superior
n the ETX is superior in terms of portability
- to an 80mm ED (Orion) (F7.5) on a full equatorial mount
n the Orion 80mm ED has a slight optical superiority in contrast
n the Orion is greatly superior in terms of FOV and cool down
n the ETX & Orion are equal on detail and near focus
n the Orion is slightly superior on deep sky viewing
n the ETX is slightly superior on chromatic correction
n the Orion is mechanically superior
n ETX is superior in terms of portability
- to an APM 102mm triplet achromat (F6) on a full equatorial mount
n the ETX is optically superior (contrast, detail, chromaticism, near focus)
n the APM is greatly superior in terms of FOV and cool down
n the ETX & APM are probably equal on deep sky viewing
n the APM is mechanically easier to use
n the ETX is superior in terms of portability
- to a Celestron C-90 (F11.1) on a camera tripod with slow-motion device
n the ETX is optically superior (contrast, detail, near focus)
n the ETX and C-90 are equal in terms of FOV, cool down, deep sky
n the ETX is mechanically easier to use
n the ETX is slightly more portable
Anecdotal Mechanical and Optical Review of the ETX90-RA
A full description of the appearance and functionality of the ETX can be obtained at the Astronomics.com website. Here, the ETX instruction manual can be downloaded. Familiarity with the maksutov-cassegrain type scope in general and the etx/questar type configurations in particular, will facilitate understanding the following comments.

Visual Performance:
Saturn: wow! The cassini division is visible each time, every time (once thermal equilibrium has been reached) as a thin dark line nearly through the whole ring system at this time. The shadow of the disk of the planet on the obscured ring is clearly visible. Polar darkening, crepe ring against the planetary disk and the equatorial band are visible. The moons are visible but not spectacularly so. The ETX gives a beautiful crisp view of the ring system and cassini at 40X. The best views in terms of sharpness are around 100X. A nice crisp view continues to be delivered up to 210X (c. 70X per inch of aperture) with a concomitant three-dimensional appearance.
Jupiter presents a very nice sharp disk up to 210X. It is in the 100X to 135X range that the ETX performs best on the Jovian detail, revealing two distinct belts, with indications of belt splits, bars and fragments of belts elsewhere on the planet and some indications of festoons. The GRS and eclipse shadows should be easily visible. The features, though visible, seem to be slightly washed out. The use of a yellow filter helps. The moons appear as four beautiful bulls-eyes.
Venus presents a nice gibbous disk at this time with no color (chromatic aberration) present.
Mars even though it is six arc seconds in size, presents a definitive disk and a hint of a dark surface feature.
The double star Castor is beautifully presented at 100X as two headlights encircled by a noticeable diffraction ring. The doubled nature of eta Orionis is clearly seen.
With a 32mm plossl providing a 1.3 degree FOV, the Great Nebula in Orion is attractively framed. At 100X the trapezium presents four perfect tiny airy disks with first diffraction rings. At 180X, in the clearest and most stable of skies, there is a hint of “e”.
With the 1.3 degree FOV of the 32mm plossl, the entirety of the Pleiades can be taken in. Stars are pinpoint across the field, as is to be expected at this long focal length.
At fifty feet, both through a window and without a window, views of juvenal blackbirds are excellent, revealing the detail of the coat as well as its iridescence. It is easy to see a sparrow work a seed’s covering apart with its thin red tongue to obtain the seed and leave the chaff. Though very pleasing, this scope is of limited “birding” potential because of its small FOV. Some nearer objects would not be properly framed.
When using attachments such as a diagonal and visual back in the rear port or an extension tube (2 inches) in the upright port, objects as near as three meters away can be focused on. Even at this near distance focus is sharp. Observations of a bubble in a window pane at ten feet illuminated by sunlight revealed numerous details that could not be seen at all upon close inspection with the unaided eye in full light conditions.



Optical Performance:
Sometimes point-light sources (sunlight reflecting off of crevices in ceramic or glass, stars) appear as tiny perfect airy disks surrounded by a bright first diffraction ring that is of uniform width but of slightly differing brightness at one end. I would call this 95% collimated. This level of collimation probably provides a degree of detail and contrast that in my eyes would be indistinguishable from 100% collimation. I obtain this degree of collimation inside the house at sun reflected point light sources, sometimes under the sky when the scope has reached full thermal equilibrium and at other times by pressuring the internal diagonal mirror in one specific direction (not advisable) or by loosening and tightening the meniscus ring. At other times there is a perfectly round airy disk with a discontinuous first diffraction ring. The ring is fully formed on one side going to a less well formed, fainter and at times disconnected appearance at the other side. Sometimes, more diffraction rings are noticed on one side of the disk than on the other. Slightly out of focus images of point-light sources reveal the central circle/point as slightly off center. I would consider this to be 90% collimated. Under most conditions this provides perfectly acceptable views such as those described above under Saturn and Jupiter, the descriptions of which were secured while observing the same under these conditions. Nevertheless, improvement of the collimation from what I am calling 90% to 95% collimated provides a noticeable difference in detail and contrast.
Intra and extra focal images of point light sources reveal a high degree of similarity. Though high optical quality can also be obtained in some optical configurations while also producing dissimilar intra/extra focal images of point light sources (of which the maksutov might be one), the presence of this similarity in a 90mm F13.8 maksutov cassegrain is a good sign. The famed double dark ring that maksutov owners are familiar with in star testing is of nearly the same dark hue on both sides of focus; the extra focal being only slightly more washed out. Both defocused images nicely collapse down to the Berrevoet’s circle, and then to the Barbour Dot and finally to the airy disk with diffraction rings. There is no indication of astigmatism in the extra and intra focal images. There is a slight indication of astigmatism in focused point light sources in slightly unstable air or in thermal disequilibrium. However, this is well below diffraction limitation if it is present at all.
A similar sized refractor may take 15 minutes to a half hour to equalize a thermal difference of fifty degrees Fahrenheit. Maksutov cassegrains of this size may take between thirty minutes and an hour for the same. Good views can be obtained between 15 and 30 minutes, with everything that can possibly be seen in a 90mm maksutov being within the visual threshold as one comes nearer to thermal equilibrium. I have adopted the technique of uncapping the meniscus lens, pointing it down, opening the rear port, inserting a visual back and a mirror diagonal and pointing it facing down to faciliate cooling and to minimize dust entering the system.
I have not used the provided 8X21 finder. However, I suspect that it is nearly worthless for optical and mechanical reasons. The 8X25 right angle finder is adequate. It provides a more comfortable position for viewing. It also provides a nice apparent field of view. However, the limited FOV and the lack of light gathering surface somewhat limits its ability as a finder. If one is comfortable with using charts and star-hop-ing from bright objects, this should be adequate. Another challenge with this finder is that the use of the three double screws can prove challenging. This challenge is augmented by the fact that the #774 original carrying case was not designed with this finder in mind. The wall of the case jams against the finder. This in turns tends to change the direction pointed. One final negative about the finder is that under cold conditions, the glue holding the objective cell to the tube and the lens to the diagonal holder tends to deteriorate, resulting in these being pulled off. One other deleterious feature is that two dust caps were not provided with the finder.
There are knobs that allow one to manually adjust both in right ascension and declination. There is a rod-attached-knob that can be used to tighten the declination setting and a knob provided to tighten the right ascension setting. In order to use the electric clock drive this knob must be tightened. The drive tends to drift a bit until it catches. Usually this drift is less than the FOV of a 32mm plossl and just about the FOV of a 12.5mm ortho. If one attempts to center the object by loosening the right ascension lock knob and using the other knob, the drift will be experienced again. I have learned to slightly adjust one of the table-top tripod legs and then re-adjust the declination. I have had little difficulty.
It is not difficult to open the back and insert the batteries. A suggestion given elsewhere is very useful; use the central leg fully screwed in and secured to pull the bottom plate off once the three screws are removed.



Aesthetics and Portability:
The metal tube of the OTA has a beautiful royal blue/purple sheen. Though invisible in lamplight, it is particularly attractive in daylight on the picnic table, on the office desk or a window table in the living room.
For those who appreciate small complete packages, this scope is very ideal. The scope, its mount, its drive and needed accessories can be carried in one hand. Within its overhead compartment allowable hard case, everything one needs can be packed. This includes the scope (ota, mount, drive), eyepieces, diagonals, legs, filters, tools, etc. Everything one needs for a night of observing can be stored in this one convenient case.
All the controls and easy to use and convenient. The addition of an EZ-Focus cord and a Visual Back increase the convenience. The plastic components, though they seem substantial enough, do cause one to treat things quite gently for fear of stripping some screw or cracking a housing. On the other hand, there are a number of ETX users who can claim up to eight years of use since the first ETX arrived on the market with no durability problems.



Price and Value:
Is the ETX worth its price? The comparison touch stone of small catadioptric maksutov cassegrains is the Questar 3.5 (89mm). Any such comparison must be subjective and contingent on many unmeasurable factors. Yet, to construct a comparison is at least entertaining and perhaps somewhat useful. To this end, the following comparison attempts to be conservatively favored toward the Questar.

% comparison of the ETX to the Questar:
Optical Quality: ETX 90% of the Questar
Mechanical Durability/Functionality: ETX 50% of the Questar
Appearance and Aesthetics: ETX 75% of the Questar
Portability: ETX 90% of the Questar
Resale Value (of purchase price): ETX 50% of the Questar


If these values are multiplied (i.e. 90% X 50% X 75% X 90% X 50%) one obtains a conservative-comparative value of .15 (.9 X .5 X .75 X .9 X .5). If we assume a new purchase price of $4000 to $4500 for a Questar, Standard Model (basic), a new ETX-RA with comparable accessories should cost $600 to $675. Currently, one can obtain a new ETX90-RA, hardcase, flexible focus cable and visual back for around $400.

Overall Rating: 9
Optics:9 Mount:8 Ease of Use:8 Value:9
Weight: 1 (Unreliable Vote)
Date:
By: Anonymous (xxx.xxx.18.49)
Link to this vote: http://www.excelsis.com/1.0/displayvote.php?voteid=342284

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