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Orion Eyepieces
Orion Eyepieces

I recently received two of Orion’s eyepieces for testing purposes: a Stratus 24mm and an Edge-On Planetary 5mm. These are two of my most used focal length eyepieces, so serve as a good test for their respective series.

Stratus 24mm

I’ve always been a bit concerned over an eyepiece series named for a type of cloud. However I’ve heard good things about this series, and have long wanted to test one.

The Stratus series is unusual in being usable in both 2” and 1.25” focusers. There is a normal 1.25” barrel, but the lower part of the main body of the eyepiece is 2” in diameter, and so fits perfectly in 2” focusers. Since the Stratus series covers a wide range of focal lengths, it means that you can switch eyepieces in any telescope without fiddling around with adapter rings.

Stratus eyepieces are available in 24mm, 21mm, 17mm, 13mm, 8mm, 5mm, and 3.5mm focal lengths. All offer a 68° field of view and 20mm eye relief, with the exception of the 24mm which has only 15mm eye relief. The eyepieces are finished in a matte black, with knurled rubber grips.

The 24mm is a particularly useful focal length because it offers just about the widest actual field of view possible in a 1.25” eyepiece, delivered at a high magnification so that contrast with the background sky is maximized. For many years I have used a Meade Super Wide 24.5mm eyepiece to fulfill this function, so naturally that was the main eyepiece I compared the Stratus with.

The telescope used for these tests was a Starmaster 11” f/4.3 Newtonian equipped with a Tele Vue Paracorr coma corrector. This lengthens the focal length by 15% but corrects all aberrations, delivering an aberration-free f/4.9 image. This is an “acid test” for eyepieces, as most are not designed to function well at focal ratios as short as f/5. If an eyepiece does well at f/5, it will be excellent in just about any telescope.

My main test for eyepieces is to examine a critical image at both the center of the field of view and at the very edge of the field of view. Both images should be identical; I look particular for a variety of aberrations: chromatic, spherical, defects in contrast, etc.

The Stratus 24mm passed all of these tests with flying colors. It was noticeably better than the Meade eyepiece at the edge of the field, where the Meade lost color and contrast. It’s worth noting that the Meade eyepiece, now discontinued, cost twice as much as the Stratus does.

In the 11” Starmaster, the 24mm yielded a pleasing 58x: powerful enough to show detail in galaxies but with an actual field of 1° 11’, putting the objects in context. As I said, this is one of the most useful combinations of focal length and field of view.

If the rest of the Stratus series is comparable to the 24mm, this makes an excellent choice for a high-quality eyepiece with a wide field of view.

Edge-On Planetary 5mm

It used to be that using a 5mm eyepiece for planetary observation was literally a pain. Classic designs like the orthoscopic and Plössl had an eye relief so short that the observer needed to cram their eye into the eyepiece to even begin to see its rather narrow field of view. About ten years ago a series of new designs incorporating Barlow elements changed all this, allowing comfortable eye relief so that anyone, even with glasses, could observe in a relaxed manner.

Orion’s new 5mm design represents the next generation of these comfortable short-focus eyepieces. Like the latest designs of ED refractors, it has a classy high-tech look with a gleaming black anodized finish. As expected, it delivers a bright, high contrast image, which can be viewed in total comfort thanks to its 20mm eye relief and large eye lens. It has a moderate 55° field of view, larger and far better corrected than any Plössl. This series of eyepieces is available in 14.5mm, 12.5mm, 9mm, 6mm, 5mm, and 3mm focal lengths.

I tested it in my 11” Starmaster the same way I tested the 24mm Stratus. Once again, the image was identical whether in the center or at the edge of the field of view. This eyepiece produced 276x magnification, which proved to be the perfect magnification for Jupiter. It passed one of the best subjective tests of an eyepiece: within seconds I’d forgotten it was even there, and was totally absorbed in the detail visible in Jupiter’s atmosphere. Once it was in the focuser, I really didn’t want to take it out…ever!

These two series of eyepieces are representative of what is now possible with computer-designed eyepieces manufactured with care. They outperform even the most expensive eyepieces of a decade ago and yet sell for prices a fraction of the so-called premium brands. Truly, we have never had it so good!

Date Taken: 05/03/2011
Author: Geoff Gaherty
Category: Accessories

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