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"
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
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
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
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.