Thanks for your input Matt. It would be interesting to see some images of the so called "Series I" and "Series II" Radians. I have always been amused by these unofficial titles given to various telescopes and accessories over the years. Takahashi is a classic example e.g. SKY-90 I, SKY-90 II, FSQ-106EDX III (is there an EDX I or II?), Teegul Sky Patrol II. To my knowledge, Tak don't use these designations, i.e. I, II or III, they have been dreamed up by vendors such as OPT, Takahashi America etc. otherwise they would label them as such.
The lens configuration in both is identical. It has to be, if it wasn't the later series wouldn't be Radians which is a patented design, they would be something else.
I have compared the 2 on a few occasions in 8mm focal length and there is very little between them optically and it would take an experienced observer in a good telescope on a good night to pick them apart. However, I am of the opinion that the later version goes slightly deeper than the early version, under excellent conditions, which indicates to me that the latter version has slightly improved coatings as compared to the early version. This is something that might be expected on an eyepiece series which was in production for about 15 years (1998 to about 2013). Similarly, the Televue 27mm Panoptic has been in production for 21 years since 1994. One couldn't reasonably expect a 1994 version of this eyepiece to be utilising coatings which are the equal of a 2015 production eyepiece.
Thanks for the information John. I have never seen the "Series I" Radians, I was a wee boy back when. All my Radians are "Series II" then but having said that, I am not splitting the set up.
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