Tolerancing is a vital stage that comes after the design phase, critical enough to warrant a re-design. It is a statistical evaluation balancing quality, cost and end-user satisfaction. The purpose of tolerancing is to determine the maximum manufacturing errors, for both optical and optomechanical components, that still produce a system with acceptable performance. Here I discuss two tolerancing techniques, Inverse Limit and Sensitivity.
Commercial telescopes are more often than not provided with a focal reducer, which enables the customer to use the telescope also for astrophotography. Here I introduce two cases where a second objective unit identical to the primary unit serves as the focal reducer to the first unit which reduces not only focal length but also design and manufacturing costs.
Cutting the optical tube length in half with a flat mirror and moving the secondary to the center of primary mirror hole is not a new idea and does nothing to help manufacture and assembly. Instead making a single mirror with a binary surface, i.e. one radius at inner zone and another in outer zone, a whole world of manufacture and assembly problems can be avoided. Assembly problems would eliminate themselves, and manufacturing would get easier by making traditional manufacturing near impossible and forcing more advanced techniques.
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.