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10 mm Clave Plossl, Televue Radian, and Celestron Plossl Comparison Part 1
I have been searching for a 10 mm pair of planetary eyepieces for a long time. Though the Zeiss 10 mm orthoscopic is regarded by many people as "the best", it is no longer available and is astronomically priced on the used market. I wanted a comfortable, high contrast eyepiece which could also be used in a binoviewer.
Paul Louis-Vinel in Paris told me "creating Astronomix I decided Clavé would not follow on its long decline and I am trying to give them a big push : with a systematic interferometry control of the products and strict specifications". I had heard that the legendary Clave quality had suffered recently and was anxious to see if the "new" Clave was as good as stated.
The Televue Radians have received rave reviews for their contrast and possess very good eye relief and a nice 60 degree apparent field of view.
Last, I decided to see what a budget eyepiece could offer. The Celestron 10 mm Plossl is a bargain at $44. I have seen no-name Plossls for much less, but these eyepieces are sometimes unreliable.
Section 1: Measurements, Appearance and Comfort
*Radian AFOV taken from TV specs, which are normally very accurate
The Radian was very comfortable to use, as expected. Even though I do not wear glasses, the generous eye relief of this eyepiece plus the sliding body made it easy to observe. I do not use the pupil guide; some people may find it useful. One disadvantage of this design is that you must hold your head relatively steady, because some people experience pupil sensitivity resulting in blackouts if their pupil is not centered over the field of view. I had no trouble during the day or night with this issue.
The Celestron has short but tolerable (for me) eye relief and average comfort. There is no light blocking eyecup.
The Clave is a very nice looking eyepiece. Its coatings are super clear and obviously superior to the Celestron in light transmission and clarity, perhaps even better than those of the Radian. One disadvantage of the Clave is it's extremely short eye relief! I found myself nearly touching the eye lens to see the entire field of view.
Like the Celestron, the Clave lacks an eyecup. One additional minor problem-both samples I received had a crack
in the field stop, visible during bright light observations. This was a very minor annoyance, but for $230 I expect
everything to be right!
Section 2: Lunar Tests (Full Moon)
My high contrast test was on the full moon, with an Astro-Physics 92 mm f/4.9 Stowaway apochromatic refractor. Specifically, I studied the Aristarchus region, with its multiple interesting rilles and mountains. Even at 45x I could see quite a bit of detail with all three eyepieces. All were sharp and showed similar detail. After an hour of switching, I gave up. Every time I saw a new detail it was due to persistent observing rather than differences in the eyepieces. The Radian has a bit more lateral color, but it was very subtle.
Off axis was a different story. The Radian was very sharp to the edge, as expected. The Celestron started blurring about 60% to the edge of the field, and the Clave was even worse! In both cases this fuzziness interfered with lunar viewing at f/4.9, and refocusing did little to help edge definition. I tried a TV 11 mm Plossl, and this eyepiece was much better than the other Plossls, holding up 75% of the way to the edge and then showing only mild blurring and distortion.
With a 2.5x Televue Powermate, the story changed...edge of field was good in all eyepieces at f/12.5, detail limited by seeing conditions.
Section 3: Solar Viewing (White Light)
Solar tests used the Stowaway with a Baader Solar Film blocking filter. The surrounding sky was a very dark gray rapidly fading to near black with all three eyepieces. Multiple beautiful sunspot groups showed excellent detail in all eyepieces, with similar edge falloff to the lunar tests. The coatings and contrast in the Clave showed in the faculae around the sunspots near the limb-this eyepiece showed them more consistently and with slightly higher contrast than in the Radian and Celestron. Both Plossls showed a slightly whiter disc than the Radian.
Section 4: Additional Observations
I only purchased one pair-the 10 mm Clave Plossls. A binoviewer plus the Claves produced a sharp image, but the short eye relief made viewing more difficult than it needed to be. I found it impossible to see the entire field of view in two eyepieces without smashing my eyelashes into each eye lens. I want to try the Radians!
Distortion was not a factor in either the Celestron or Clave Plossl. The Televue 11 mm Plossl that I used for comparison has a mild but noticeable amount of distortion which is a tradeoff for improved edge quality. The Radian shows double stars as constant distance throughout the field-its rectilinear distortion is only that inherent in a 60 degree astronomical eyepiece.
Stars at the edge of the field were much more forgiving than lunar or solar surfaces. Nevertheless, while observing Saturn during twilight Titan was barely visible with direct vision in all three eyepieces. In the Clave and Celestron Plossls, it vanished in the outer third of the field! The Radian showed the moon all the way to the field stop, as did a 10.5mm Pentax XL. This observation supports Televue's contention that aberration control increases limiting magnitude in the edge of many complex eyepieces.
Section 5: Concluding Thoughts
The planets are too low to do an effective comparison. However, the solar tests bode well for the Clave on low contrast extended planetary features. That being said, the difference between all three eyepieces was subtle, and persistence at the eyepiece will often overwhelm ones initial impressions.
Televue eyepieces continue to shine in fast scopes, and for most applications the Radians would be an excellent choice. Even Televue Plossls have superior edge correction, especially compared to the much more expensive Clave.
The Clave MAY have a place for a dedicated planetary observer who has a slow scope, no glasses and who requires the ultimate contrast. For most, the possible slightly increased contrast of the Clave is offset by increased edge aberrations and very short eye relief.
The Celestron was a surprisingly good performer-there was not any detail visible in either the moon or sun which was invisible in this eyepiece. Given the $44 pricetag, it is by far the best bargain and I would be happy to have this eyepiece among Naglers and Panoptics.
Daytime comparisons, more measurements, planetary observations and perhaps some deep sky next fall-winter...