Previously I have discussed an automated optimization method for designing a fast four lens refrative objective that uses symmetrically manufactured lenses (you can catch up about it from this downloadable pdf). The original development model used glass from Schott, but next I will discuss how it won’t make much difference which glass manufacturer one uses.
Giving new life to an old telescope design is quite possible and not necessarily expensive either.
I designed a generic Fraunhofer doublet telescope in order to design two accessories for it using nothing but Schott N-BK7 glass. Both accessories address the astigmatism in a doublet, flattening the image plane for a wider field of view of the original doublet.
Commercial astronomical telescope optics development has followed a straight tangent for decades now. Focal lengths have shortened while image sizes have grown. Refractive telescopes houses five or even six lenses, making them more and more like over-sized camera optics, driving up manufacturing costs fast. Producing more and more expensive and generic products for smaller and smaller range of enthusiasts does not pay back development.
Originally suggested by Maksutov, a Maksutov microscope objective (or eyepiece) is a reverse Gregorian type reflective objective. It has high numerical aperture and has corrected spherical, coma and color aberrations. It requires a field flattener to correct the field curvature, but for on-axis observations, it has a long working distance and short total track.