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Home / Orion "Short-Tube" 120mm f/5 Refractor
by Robert Piekiel 12/17/09 | Email Author

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One can spend a whole lot of money on modern refractors in the 3-5 inch range. This easily gets into 4 figures if you have decided on something exotic like fluorite or ED glass, or triplet or apochromatic lenses.

A fast, short-focus refractor is basically a “rich-field instrument.” It is designed to work best for low-power, wide field viewing and imaging. Personally, I LOVE the views of a good, RFT, but since I’m not a career-imager, I really don’t want to spend thousands of dollars on a telescope that I use mainly for “pretty views” of extended objects like nebulae or clusters.

A while back I bought an Orion 100mm short-tube refractor. With the mount, I paid roughly $450 for it. I loved it so much, I decided to up the ante and try the larger, faster, 120mm model. I ended up finding a used OTA for about $200 and it was some of the best money I’ve ever spent.

The 120mm f/5 Orion refractor is actually a generic import. This same scope can be found from several brands, some painted black, some blue, etc, but in essence it’s really the same instrument. It sports an inexpensive 2-inch R&P focuser with a dovetail slot molded in to the casting for mounting a finder.

The scope has all the light-gathering power one would expect from a 120mm aperture, with a very fast f/5 speed, meaning that it is possible to get binocular-type low-power wide fields, or modest-power views, all with a typical assortment of eyepieces that we all probably already have.

Visually, the scope is excellent at low power on large, extended objects, such as M42, M31, the Pleadies, the Double Cluster, etc. There is some color in the stars, but to me, it’s acceptable, and I choose not to try to correct it with a minus-violet filter.

The moon is stunning, and despite the colored edge, shows excellent contrast and sharp definition. You can even hand-hold the scope for low-power sweeping. It’s quite manageable to use without a mount.

If you try to increase the magnification past 100 or 150x, the color fringing will get objectionable, however, so don’t expect this scope to do well on planets or tiny objects.

Photographically, the scope excels at wide fields, especially if you use a bit of image-processing to get rid of the false colors. Does the scope perform as well as a Tele Vue, for example? No. There is some color to the stars, and the images are not quite as sharp, but when you consider the price difference. ($369 is an approximate retail price for the OTA) it is well worth the value.

My recommendation: Get one of these with a not-too-expensive 2-inch diagonal and an Orion 26mm Q70 eyepiece. Treat yourself for some of the prettiest rich-field views that a little money can buy.



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