|
In short:
1. If you have a fast newtonian buy TV eyepieces and forget the rest.
2. If you have a refractor, buy Japanese eyepieces (Vixen, Pentax, Nikon, Masuyama).
3. If you have an SCT or mak, any modern eyepiece will work well enough.
The long:
The TV eyepieces - being American - are primarily suited to the US market which is dominated by big dobs ie fast newtonians, followed by SCTs. Hence most of their eyepieces suit fast newtonians.
In Japan the most popular scopes are small refractors and hence the Japanese eyepieces primarily suit that target market. Why does this matter ? What's different is:
1. The curvature of the focal plane of the refractors (convex) vs that of newtonians (concave), and eyepieces should ideally have field curvature to match so that the whole focal plane is in focus at once;
2. Fast newtonians have coma off-axis, its an inherent property of a parabolic mirror. Refractors do not.
Looking at Al Naglers (TV) patents shows that some of his designs had a modest amount of negative coma to partially compensate for that of a newtonian (better than none), yet in an SCT at f/10 the effect was not noticeable.
|