Comparison of three 6mm eyepieces

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John Fitzgerald United States of America
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Comparison of three 6mm eyepieces

#1

Post by John Fitzgerald »


I was able to borrow a 6mm Radian from a very generous fellow amateur astronomer, and tested it as follows:

The night of July 2, 2021 was clear, and decent, but not perfect, seeing. I compared the Radian 6mm extensively with my 6mm Delos, and my 6mm TMB Planetary eyepiece. I had all three of them in my Tak turret on my 6" f/8 apo refractor at the same time, switching back and forth. Of course, I had to refocus a bit each time. Also, briefly compared them to a 7mm TV Delite.

The Delos is almost heavy and long enough to make the turret turn; when on the side, only a light touch was needed to turn it under, being opposite the Radian. The other eyepiece in the turret was a 20mm ES 68 degree, used for initial centering of objects.

The test targets were Nu Scorpii, quadruple star, Eta Draconis, and Struve 2054, the very tight (0.9") double next to Eta, and finally, Saturn.
The Radian performed on a par with the other two, resolution wise, was sharp to the edge, and has about the same light transmission. The same faint field stars were detected with all three.

As specified, the Delos has a larger field, but was not quite as sharp at the edge as the Radian and TMB, but was equally sharp at 60 degrees, or maybe out to 65 degrees. The TMB field is only 55 degrees, detectable as a tiny bit less than the Radian's field. In the Delos, the edge sharpness may possibly be a result of limitations of the scope itself, given the wide field.

The Radian is a bit warmer in color than the other two 6mms, and definitely warmer than the 7mm Delite. On Saturn, the color difference was more noticeable, with the TMB the whitest of the three, but definition was essentially the same with all three, with cloud bands and the Cassini division being easily seen. This particular 6mm Radian is slightly heavier than the 7mm Delite, but of course, not nearly as heavy as the Delos.

I experienced another decent seeing night the evening of July 3, and tested the three 6mm eyepieces in a 10 inch f/5 Newtonian on an equatorial platform, with much the same results. The 6mm Radian, IMO, is just as good as the Delos, out to the limits of the 60 degree Radian field.

I did notice a bit of color on bright stars in the Radian when at the extreme edge of the field, but that happens at the extreme edge on the Delos too, just further out. The Radian's color rendition is a bit more yellowish than the Delos and Delite.

Definition anywhere in the center 50% of the field is essentially the same with all three of the 6mm eyepieces I tested (at f/5 with no Paracorr). The 6mm TMB at f/5 isn't quite as good as the other two about 60% or so out from the center to edge, but is their equal in the center at f/5.

The 6mm Radian is just as good as the 6mm Delos over all, in my opinion, except for narrower field, and the slight yellow bias in color rendition, which may actually help slightly if used in an achromat.

These observations are my opinions only, as a long time visual observer, experienced with a variety of instruments. Personally, I prefer the Radian over the Delos, because of the excessive length and weight of the Delos. I really don't need the wide field at 6mm, because it's generally used in driven instruments. YMMV.
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Bigzmey United States of America
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Re: Comparison of three 6mm eyepieces

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Post by Bigzmey »


Thanks for the shoot out John. At the time I had a few Radians I did not have Delos or Delites to compare, but Radians stroke me as good performers on planets, Moon and doubles. They were step above Celestron X-cel LX and DualEDs, sharper and with less light scatter. The only annoying thing were the loose eyeguards.
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Re: Comparison of three 6mm eyepieces

#3

Post by Makuser »


Hello John. I very much enjoyed your review/article on the three 6mm eyepieces. I have one of the three that you tested. It is the TMB Optical Planetary II, and is a 6 element with a 58 degree AFOV. My other is a Smart Astronomy clone of the Orion Edge On Planetary, and is a 7 element with a 55 degree AFOV. I ran an A-B comparison of the eyepieces years ago with both my 90mm and 180mm Maksutov Cassegrain telescopes. Both had excellent high contrast, and were tack sharp. The Smart Astronomy had a slightly better sharpness near the edges of the field as you might expect.
6mm eyepieces.JPG
Thanks for your great report and interesting read John, and the best of regards.
Marshall
Sky-Watcher 90mm f/13.8 Maksutov-Cassegrain on motorized Multimount
Orion Astroview 120ST f/5 Refractor on EQ3 mount
Celestron Comet Catcher 140mm f/3.64 Schmidt-Newtonian on alt-az mount
Celestron Omni XLT150R f/5 Refractor on CG4 mount with dual axis drives.
Orion 180mm f/15 Maksutov-Cassegrain on CG5-GT Goto mount.
Orion XT12i 12" f/4.9 Dobsonian Intelliscope.
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John Fitzgerald United States of America
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Re: Comparison of three 6mm eyepieces

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Post by John Fitzgerald »


Bigzmey wrote: Mon Jul 12, 2021 4:44 pm Thanks for the shoot out John. At the time I had a few Radians I did not have Delos or Delites to compare, but Radians stroke me as good performers on planets, Moon and doubles. They were step above Celestron X-cel LX and DualEDs, sharper and with less light scatter. The only annoying thing were the loose eyeguards.
The loose eye guard can be fixed by removing the eyecup from the bottom, then removing, compressing, and reinstalling the internal springy ring. Mine are all good now.
Double and multiple star observer. Over 3,500 unique pairs logged.

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