I've often read that barlows "add correction" in the form of correction for spherical aberration. How strong is the effect, and is it any value on telescopes with spherical mirrors? That is, would it be beneficial to always use a Barlow in conjunction with a spherical mirror telescope and then choose eyepieces around it?
Also, do Barlows also reduce eyepiece astigmatism at all? Presumably a Barlow will shallow up the light cone of the telescope since it effectively increases its focal length. Does this have an impact at all on the level of astigmatism present in cheaper eyepieces that would otherwise not work well with fast focal ratio telescopes?
Edited by CrazyPanda, 20 May 2019 - 09:04 PM.