OK it's a conventional Schmidt, with a triplet corrector - and they evacuate the interior. What's really interesting on page 6 is how dew/frost is managed:
"A conductive indium-tin-oxide (ITO) coating is employed as one of the layers of the anti-reflection coating on the interior surface of the window, to act as an electrical heater that replaces energy lost through black body radiation into the cryostat. Without such heating the center of the window would equilibrate to a temperature well below freezing causing condensation and cold convection cells which would degrade image quality. With 150 Ω/square sheet resistance, about 316 mA at 47 VDC is required to dissipate 15 W typically required to offset the radiative cooling. Electrical contact is provided by a thin copper foil sandwiched between the window and Viton support gaskets running most of the width of the window at North and South edges. Power is scaled according to the Stephan Boltzmann law for radiative transfer using measured tube and CCD temperatures, with scale factor calibrated using a thermal imaging camera in the lab."
Now that's what I call neat. With a little thought that could be applied to SCT's, if Synta bothered to do a little product improvement - for amateur sized scopes it would scale perfectly to work at 12VDC with a PWM controller.
Could even be laid out as a complex path, like that used for car rear window heaters.
Edited by luxo II, 27 January 2023 - 01:26 AM.