We shall describe here the main features of the PSPT telescope, in its definitive version, according to the conditions of the three sites. Small differences among the three systems do not affect the validity of the present overall description.
The PSPT is a refracting telescope with a small diameter, working on the diffraction limit and acquiring full-disk images of the Sun through three interferential filters with a relatively narrow band. The telescope, endowed with an equatorial mount and a computer-controlled time movement, has an optical design which lowers the level of scattered light in the instrument.
The images are acquired by a CCD 2048×2048 detector, with a very short exposure (generally of the order of 40ms). In order to increase the photometric accuracy of acquired data, several exposures are joint so as to create a single image.
An active mirror stabilizes the image field so as to prevent a series of exposures from significantly affecting the resolution quality of the acquired image.
The system also includes a scintillation monitor as well as flux channels, which can be used to measure the change in atmospheric transparency during the acquisition as well as to select images.
Telescope sighting and the movement of its mechanisms are controlled by a software running on PC 486 and DSP (Digital Signal Processor), whereas data acquisition and system check during acquisition are handled by special programs in C e IDL language, running on a Sun Ultra Sparc 1 workstation.