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Orion VX80 Altazimuth Refractor (The "other" 80mm telescope)
I recently decided that the ideal grab-and-go scope would be a small, long-focus refractor on an alt/azm mount. The Orion VX80 (80mm f/11.4). Altazimuth Refractor (aka Vixen Custom 80M) seemed to fit my idea. The mount is the Vixen Custom Alt/Azm and, in my opinion, the wooden leg tripod really makes the setup very attractive. (Vixen also offers the mount with aluminum legs but Orion does not offer that version.) I tend to agree with the Orion ad-copy which calls the VX80, "the classiest-looking telescope made today". I didn't buy it just for looks though. My intention is to use it as a grab-and-go scope in the backyard - mostly for double star work.
The VX80 comes with a 26mm Plossl, a dove-tail mounted 6x30 finder and some tools for adjusting the mount. A small round plastic accessory box is included - it looks like Tupperware and even has a plastic lid like those used on Tupperware bowls. The box bolts to the tripod spreader with a single wing bolt at the center and really works quite well. An optional metal tray is available but it must be removed in order to fold the tripod while the green(!) "Tupperware" box allows the tripod to fold almost all the way even when the box is in place. A 1.25-inch erect image diagonal is also included but I have not used it - instead, I use a Lumicon 90-degree mirror diagonal.
I wanted an alt/azm mount for its minimum weight and ease of use. The lack of counter weights keeps the total weight down and an alt/azm mount makes for quick and easy setup. The Vixen mount folds easily without having to remove any bolts and, even with the scope and an eyepiece in place, weighs less than 20 pounds. It's really nice.
How easily and precisely the scope can be moved in both directions is important. Coarse movement of the VX80 in azimuth is accomplished by loosening the azimuth clutch - a plastic knob - and pushing or pulling the optical assembly. After tightening the clutch knob, fine azimuth movements can then be made using the slow motion control. Altitude friction is adjusted by two 19mm locking nuts on the mount. Quite a bit of friction is required to keep the scope from moving unintentionally (especially when viewing near zenith). There is no clutch for altitude movement so the altitude slow motion control is effective at all times.
Both of the slow motion controls have limited travel. If you find you've moved the slow motion control to the
limit (which is really quite a ways), you'll need to "re-wind" manually to center the controls. The slow
motion movement ratio is very good - it's quite easy to track at high powers. Altitude control is very precise
with no noticeable backlash. Azimuth movement, however, has a lot of backlash - reversing directions requires turning
the azm knob about a quarter turn before movement of the telescope resumes. I've read other users have eliminated
much of the azimuth backlash by using shimstock but I have not examined the mount enough to know where or how the
shimstock would be used. To this point the backlash has not really been a problem for me since tracking does not
require reversing directions in azimuth.
The mount is very sturdy even when the tripod legs are extended to near maximum (60 inches). The generous height is, by the way, very nice to keep the eyepiece at a comfortable height when viewing objects near zenith. Bumps dampen immediately - much better than a friend's TV Gibraltor mount (with TV-102). This fast dampening really helps because the scope's 1.25 inch focuser movement is pretty stiff. Although I've adjusted focuser friction using the screws underneath, it seems the focuser would benefit from lighter grease. This is probably more a user preference (and I don't use any heavy eyepieces) and I prefer a focuser with a lighter touch. The focuser does have a locking screw.
The optical assembly is about 36 inches long and attaches to the alt/azm mount with two tube rings. The tube rings are not the standard clam-shell type rings but rather are captive rings which can only be removed from the OTA by removing the dewshield/optic cell and sliding the rings off the end of the tube. The front ring has plastic-handled bolt underneath that tightens onto the mounting plate directly. The rear ring has the tightening bolt on top of the ring - it compresses the ring to the OTA, causing the ring, in turn, to grip the mounting plate. It would have been much more convenient for me if the usual clam-shell type rings had been used. That would have allowed the scope to be moved between the alt/azm mount and a second mount (say a GEM) easily.
The jury is still out on the optics (80mm f/11.4) because of less-than impressive star tests but I still found the in-focus images to be very good. Stars are nice points with no sign of astigmatism, and are generally sharp to the edge of the field of view. The "generally" qualifier is added because I found stars right at the edge of the field were a little fuzzy when I used the 30mm Ultima eyepiece. I'm really not sure which component is the problem in that combination.
The Double-Double in Lyra splits cleanly at 91x (10mm Ultrascopic) . On nights of good seeing, the stars are nice small disks with just a hint of one diffraction ring around each star at that power. At 51x (18mm Ultima) I thought I could see elongation of the doubles.
At a dark site the VX80 did very well. (I compared views in the VX80 with those in my friend's TV-102. The views in the 102 were mostly through a 12mm Nagler (73x), 8mm Radian (110x). The VX80 setup could not nearly keep up with the 102 as far as limiting magnitude and field of view so my concentration was strictly on images at the center of the FOV when making comparisons. I have/had no delusions about the VX80 offering views comparable to the TV-102.) M11 was a nice bright object in the VX80. There were a handful of stars resolved on top of a bright nebulous patch. M57 was also bright and easily located. The ring shape was obvious, although small.
Stars to about 10.5 magnitude were easily seen in the VX-80 at the dark site. I viewed no extended objects except the bright planetary M57. The bright globular M13 was easily seen but stars in it were at the edge of showing resolution - more granular - with a few stars seeming to resolve with averted vision.
The VX80 star test shows quite a bit of spherical aberration (with and without the diagonal in place). Comparing the views with images produced by the Aberrator software (Ver 2.53) indicates about .20 wave 5th HSA. This really surprised me because even the 80f5 Chinese scopes I've owned showed better correction in a star test. On the other hand, the VX80 handled my 4mm UO orthoscopic very well at 227x while my current 80f5 shows nice correction in the star testing but its images begin to break down at about 90x. At 227x in the VX80, stars were nice airy disks with 3 diffraction rings - none of which seemed overly bright, the 3rd ring was very faint. Some shading was even visible on Mars at that power although the image was understandably soft. I expect more experience with the scope will show that around 180-190x will be the upper useful magnification on most nights and I consider that very good for an 80mm telescope. The fact that the images looked as good as they did at 227x was still impressive.
I saw very little chromatic aberration in the VX80. I consider solar viewing with a Baader filter a pretty tough test for color but I saw very little color in that use. Especially when careful to keep on-axis at the eyepiece it was really hard to see any purple in that test. Sunspot detail and faculae, even near the center of the disk, were very distinct.
The dewshield is metal and screws on to the optic cell which, in turn, screws on to the tube. The user manual includes instructions for collimating the scope by using 3 pairs of push/pull screws in the cell. I don't see those screws though, so apparently the instructions apply to other Vixen scopes - perhaps the apochromatic models. Luckily my scope appears to be in good alignment - both with and without the diagonal in place.
I think the VX80 Altazimuth Refractor will work very well for my backyard sessions and I look forward to using it on Jupiter and Saturn this winter. The scope is, though, best suited for casual use. In my opinion, the VX80 works very well for observing double stars and solar viewing. And, it should do nicely for casual use on Jupiter, Saturn and the moon but 80mm is just not enough aperture for serious deep sky observing. The maximum field of view is only about 2 degrees, so in some ways, a rich-field refractor, like the 80mm f/5 is better suited for large bright clusters and scanning the Milky Way. The VX80 should work very well for terrestrial use although I haven't used it for such and don't really plan to.
Orion currently (November 2001) sells the VX80 Altazimuth Refractor for $689 USD plus shipping. This seems a little high, in my opinion, for such a small achromatic scope but the scope and the mount are of very good quality mechanically. And, as stated above, the setup is very attractive - if that means anything to potential buyers.
As I understand it, the Vixen 80mm f11.4 was also sold by Celestron as the Premium 80 until a few years ago but the less expensive Celestron Firstscope 80 and mounts now sold by Celestron are made in China. The Vixen Altaziumuth mount is similar in appearance to the alt/azm mount sold by Orion as the AZ-3 but I suspect the Orion mount is made in China by Synta.
I've been an avid observer for about 5 years. My other telescopes (past & presently owned) include a Criterion RV-8 Dynascope, Celestron Celestar 8 Deluxe, Orion ShortTube 80, Celestron NexStar 80GT, Meade ETX-90RA, and a Bresser 120mm achromatic refractor. I also frequently observe in friends' 12.5-inch and 20-inch StarMaster Dobs and the TV-102. My most-used scope is the RV8 which I use 5-10 times per month in the dark skies and moderate climate of West Texas.
Eyepieces used in the VX80
30mm Ultima 30x 1d39m
26mm Sirius Plossl 35x 1d26m
18mm Ultima 51x 1d
10mm Ultrascopic 91x 34m
4mm UO ortho 227x ~11m