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Orion Astroview 100mm f/6 Review

This is an informal equipment review, written in June, 2003:

For the last few months, I've been looking for a small, portable scope to complement my 12.5" Dob. Many years ago, I got an Astroscan (a 4.25" Newtonian) as my first scope, and though I still have it, I wanted something of somewhat higher quality and lighter weight.

My main criteria were (a) portability; (b) good wide-field viewing capability, (c) good value for the price, and (d) no immediate need for a better mount. I have a better-than-expected camera tripod, which has held the Astroscan for many years, and I wanted the scope to be small enough to work with it. A true astronomical mount would be better, but for now, the camera tripod will do.

After some investigating, I decided to get the Orion Astroview 100, which is a short (f/6) 100 mm aperture refractor. This scope is similar in spirit to the ubiquitous 80mm f/5 "short tube" refractors, but it's a little larger all around, and (to my mind) has more solid construction.

The Astroview 100 comes with a 6x30 finder, 90 degree mirror diagonal, 2 inexpensive Plossl eyepieces (10mm and 25mm), and a collimating eyepiece (an inexpensive Cheshire). It weighs about 7 pounds with all accessories in use (about 4 less than the Astroscan).

My first impressions, in the daytime, were favorable, given the inherent limitations of a short refractor. I put it on my old camera tripod setup and checked out a few daytime targets. High-contrast objects (such as the edges of buildings and trees against a bright sunlit sky)
showed some purple color fringing, which is to be expected. The color doesn't seem to be any worse on daytime subjects than in an Orion 80mm f/5 I got to use recently. A 100mm scope is overkill for most terrestrial use, but this one is still light enough to be usable.

One quirk I noticed: this scope does not come to focus with the supplied eyepieces (or any others I tried) without the diagonal. This isn't a problem for astronomy, since ordinarily I'd use a 90 degree diagonal all the time, but for daytime use I wouldn't need a diagonal for many targets. Not a major problem, but something I thought was odd.

First light was June 5, 2003. I tried a fairly wide range of targets, predominantly with the included 10mm (60x) eyepiece.

  1. Moon (not quite 1st quarter): (60x) There was purple fringing at the limb, of course. Otherwise, the image was very clean, with extensive detail seen along the terminator. I believe, though, that I wouldn't want any more chromatic aberration than this. I'd like to compare to an 80mm f/5 sometime.

    The lens cap comes with a removable center cap that exposes about 50mm of the lens. This effectively turns the scope into a 50mm f/12, which has negligible false color even on the Moon. I find that for most other objects, I'd rather have the brighter image and the higher resolving power of the full aperture, despite the greater chromatic aberration.

  2. Jupiter (24x, 60x): Unfortunately, very low, and seeing zapped a lot of the fine detail. 2 bands seen easily at 60x. There was a bit of a violet halo around the planet, but it didn't seem to hurt surface detail much. I'd like to see it at a higher altitude sometime -- may not happen till next year though.
  3. M13 (60x): With averted vision, M13 was grainy across much of its width, with some true resolution at the edges. Not bad for a 4" scope at low power in town. A little more magnification would probably help quite a bit.

    This was a fairly severe test of my cheap mount, since M13's altitude was about 75 degrees at the time. I really had trouble only with fine motions, because of tightening the head a little more than usual. The overall stability of the telescope was fine; I had no feeling that it was unbalanced.

  4. M5 (the Ring Nebula) (60x): Definitely a ring with a darker center, not just an oval smudge.
  5. Polaris (60x): The 9th magnitude companion was dim, but not difficult. I didn't notice any significant color around Polaris itself.
  6. Vega (60x): Vega *did* have a prominent violet halo. This is expected in a scope of this design and focal length, so I'm not complaining.
  7. Double double (epsilon Lyrae) (60x): A pleasant surprise: even at just 60x, I could tell there were 4 stars, with some black space in the wider of the two pairs. This is quite different from the Astroscan, where I typically needed around 100x to be sure, and the split still wasn't clean.
  8. Albireo (beta Cygni) (60x): The color contrast (blue - yellow) is very striking. The blue star seems to be a trifle bluer than in reflectors I've used, though I'm not sure the effect is real.

I tried a Meade 18mm SWA eyepiece (33x) as well as the stock Plossls (24x, 60x) and a 21mm Televue Plossl (29x). The edge performance of the 18mm Meade was worse than it is in my 12.5" f/5 Dob, which seems strange. Star images get soft about 50-60% of the way out to the edge and downright blobby about 80% of the way out. I actually preferred the view in vanilla Plossls despite the narrower field of view.

Overall, my impressions are favorable, especially considering the price tag ($250), which is a good deal less than that of my old Astroscan after considering inflation. Star images are generally much sharper, and the telescope itself is lighter. It's also more portable, oddly enough -- although an Astroscan itself is shorter than the Astroview 100, you have to cart around the Astroscan base and a tripod bracket, which adds up to a fair amount of extra bulk.

I'm not sure I'd recommend this as a *first* scope, however. I would rate it above the Astroscan, and probably the typical 80mm f/5 refractor as well. However, a lot of folks start with the Moon and planets, and the chromatic aberration in a 100mm f/6 is still significant on these targets. I don't find it intolerable, but other folks have different tolerance levels. Orion's 90mm f/10 might be a better beginner's scope -- still fairly portable, but with much less chromatic aberration.

On the other hand, so far it fits the "second, grab and go scope" quite nicely for me. It's large enough to show good detail on the Moon, planets, and brighter deep-sky objects while not being too cumbersome to set up. There seems to be a break point at about 4" to 4.5", at which many targets get a lot more interesting compared to even slightly smaller apertures. I will have much more to say after I take this little fellow to the Nebraska Star Party and see the summer skies with no light pollution.

Since then, I've put this telescope on a better mount (an inexpensive German equatorial) and tried it on a number of other targets, with generally positive impressions. My favorite observation so far: following Ganymede across the disk of Jupiter. No, not its shadow -- the satellite itself. This was challenging, but not right up against the limits of either the telescope or my ability.

In general, these inexpensive imported refractors do pretty well for the price. I've heard better things about the ones that are f/6 (like this one) and up -- the quality control on the really short lenses is a bit rocky. Unfortunately, Orion discontinued this particular package a while ago and replaced it with an OTA-only package (no finder, eyepieces, or other accessories) for the same price.

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