Does this mean that owners of non-Petzval refractors (about 98% of us on this forum) should dump their refractors so they can use Tele Vue eyepieces?
Sounds like the Tail wagging the Dog.
It seems to me that for refractor owners that can no longeraccommodate small amounts of field curvature, the task becomes finding a field flattener.
This thread is about understanding field curvature and how it relates to focal length and focal ratio.
Field curvature is an aberration, it's one that can be corrected if you want to.. it's like coma, spherical etc, people generally put up with some..
Field flatteners are a possible solution but they must be properly spaced and there's only one i know of that can be used with a diagonal. The advantage of a Petzval is that it's always properly spaced because the Petzval elements are fixed instead of moving with the Focuser. They're also matched for other aberrations, the TeleVue and Taks have ED glass front and rear.
Field curvature is primarily a low power wide field phenomenon and quickly disappears with narrow fields since it's related to the square of the off-axis distance.
I suspect most people use a strategy similar to mine. Low power, wide field means short focal length and fast. That means eyepiece's that are well corrected for off axis astigmatism. There's not much use in having a flat focal plane if the stars are astigmatic.
That's where it starts. The 31mm Nagler is the classic.
And the 31 Nagler and other similar eyepiece's do very well in longer scopes.
I happen to have a scope corrected for field curvature but I do a lot of wide field observing with shorter focal length scopes, an ST-80 with a 2 inch Focuser. It'll do 6.6° with the 41mm Pan. From the center to the edge, there's about 2 mm of difference. It's very obvious.
I just accept it, it comes with the territory. The NP-101 view has an extra special quality because the stars are in focus across the field but such perfection is unnecessary for enjoyment of the universe.