Всегда считал, что в Кеноне 45,5 , а в Никоне - 46,5... Виноват.
А допуски, вроде, зависят от размера кадра, для мелких чипов +-3мм.
И вот ещё перехватил переговоры
I asked Al Nagler about using the Paracorr with a 10" F2.8 parabola for a
CCD camera at 5.4 mm semi-field. The answer was:
"Using a BFL of about 52mm (instead of the nominal 56mm) you'll get about
0.006mm RMS spot radius uniformly over the field. This is about a factor of
6 reduction in edge-field spot size of a parabola alone."
Very interesting and an easy way to make a fast CCD astrograph without
having to make the corrector yourself. I suppose that fiddling with the
conic constant of the parabola could make it even sharper in the center.
