Quote:
Originally Posted by Wavytone
I am absolutely *sure* you know Plossls have negative coma and field curvature which just happens to match short focal-length newtonians.This is why such a simple eyepiece has survived so long, and continues today as a very good budget eyepiece among the users of short Newtonians.
I simply do not accept the makers of premium eyepieces - and I put Teleview, Explore, Pentax, Vixen and Nikon in this group - are not aware of the tradeoffs to be had by designing eyepieces to match about 50-60% of the field curvature and coma of the average light-bucket (a fast newtonian say 30cm f/4.5) on the basis that this will be equally a match in a smaller refractor (10-15cm f/7) or the average 20cm SCT.
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This is patently untrue. The only eyepiece with deliberately designed-in coma was now defunct Pretoria.
Televue, Pentax, Nikon etc will
never design an eyepiece to match light-bucket (fast Newtonian) aberration pattern, primarily as their main telescope production are premium refractors. It wouldn't make sense for TV eyepiece to show coma and field curvature in one of their their ultra corrected, flat field refractors, would it?
You have also mixed things up; Newtonians have opposite field curvature to those of short refractors/SCTs. Say you design your premium eyepiece to match a ROC of a fast Newtonian, it would then be absolutely horrendeous in a SCT.
Not a smart market move, is it?