My personal opinion is that the Powermate is a better choice if your goal is to fill magnification gaps in medium focal lengths or gaps in both medium and short focal lengths, especially with eyepieces having relatively few elements such as Plossls, Abbe orthos, RKEs, Kellners, some Erfles, and most Konigs. A Powermate is also more convenient than most Barlow in that it is approximately parfocal even in star diagonals.
When used with most Naglers, Radians, and Pentax XLs, I think there isn't a lot to recommend one choice over the other.
However, for purely short focal length use in a fast telescope (the point is that the effective field stop diameter involved is very small), I prefer a good doublet Barlow (specifically the 1.25" 2x Tele Vue model in my case) since there is less glass, fewer air-to-glass surfaces, and little divergence to speak of anyway.
So what eyepieces do you plan to use it with and in what scopes?
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Mike
When used with most Naglers, Radians, and Pentax XLs, I think there isn't a lot to recommend one choice over the other.
However, for purely short focal length use in a fast telescope (the point is that the effective field stop diameter involved is very small), I prefer a good doublet Barlow (specifically the 1.25" 2x Tele Vue model in my case) since there is less glass, fewer air-to-glass surfaces, and little divergence to speak of anyway.
So what eyepieces do you plan to use it with and in what scopes?
--
Mike
