The calibration unit of the ESO SOXS telescope which Incident Angle is developing for FINCA at the time of writing this, operates over a wide spectral range from VIS to NIR. In order to achromatize the collimating lenses, the indices of refraction had to be recalculated.
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.
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.