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I currently have a 7mm Nagler T6 and a 7mm Pentax XW that I have compared extensively over the past 2 months on a large number of targets. I have also used the 5mm,6mm and 8mm Radians extensively. In focal lengths less than 10mm the Pentax XW's are slightly better performers than Nagler T6's or Radians IMO, from the widefield/ultrawidefield designs. The Pentax has fractionally better contrast, sharpness and light throughput. Importantly to me, it has a much cooler more neutral colour tone. ie. whites look white not coffee coloured.
That having been said, there isn't much between any of them. The Nagler has a larger TFOV and its coffee coloured tones help to accentuate some surface detail on Jupiter. The Pentax is more comfortable to use than the Nagler. While the Radian is clearly 3rd pick behind two exceptional eyepieces, it is an outstanding eyepiece in its own right and at the current selling price represents exceptional value for money. Like the Nagler, it has an inherent "coffee" tint and works well on Jupiter. You would certainly be very happy to own any of the three eyepieces. Over 50% of people would never pick a difference between any of them. I can also add that the 13mm Ethos is the first Televue eyepiece I have used that exhibits cool neutral colour tones. It does not have the warm coffee coloured tint inherent in the glass types/coatings used in the Plossls, Naglers and Radians. I may also add that the colour tone of an eyepiece is a personal thing and many people prefer the warmer tones of televue eyepieces. I don't.
As specialist planetary eyepieces Zeiss Orthos, Pentax SMC orthos, Nikon orthos and Brandons are all superior to the premium widefields. Unfortunately, the eye relief is short and the AFOV narrow.
As a mid focal length widefield I would also recommend the 17mm Nagler T4. It is an outstanding eyepiece.
Cheers
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