Mem. S.A.It. Vol. 74, 667 c  SAIt 2003 Memorie della C. Fazzari 1 , I. Ermolli 1 , M. Centrone 1 , S. Criscuoli 1 , and F. Giorgi 1 INAF Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone, Italia e-mail: name@mporzio.astro.it Abstract. In response to the need for both measurement and interpretation of irradiance variations, two PSPTs (Precision Solar Photometric Telescope) have been designed and produced in the framework of the RISE (Radiative Inputs of the Sun to Earth) project, to provide high-precision (0.1%) photometric obser- vations of the solar disk, with about 1 arcsec spatial resolution at three wave- length bands. As well known, these two PSPTs, installed at the Rome and the Mauna Loa Observatories, since 1996 provide daily observation of the Sun avail- able to the community at the internet addresses http://www.mporzio.astro.it and http://www.rise.hao.ucar.edu. We present the results obtained analyzing the qual- ity of the images acquired by the two PSPTs, with particular regard to photo- metric accuracy, spatial scale, scattered light level and temporal variations of the image quality. Key words. Instrumentation – Image processing – Solar variability 1. Introduction The PSPT is a small (15 cm) refract- ing telescope designed to provide high- precision (0.1%) photometric observations, utilizing a simple optical design to mini- mize scattered light contamination and an active mirror to reduce tracking errors. The PSPT telescope has been produced by NSO of Sacramento Peak as part of the RISE (Radiative Inputs of the Sun to Earth) project; since Rome Observatory Send offprint requests to : I. Ermolli Correspondence to : INAF OAR, Via Frascati 33, 00040 Monte Porzio Catone participates to it, a PSPT has been in- stalled at the Observatory in February 1996. From 1999 a second PSPT, operated by High Altitude Observatory, is working at Mauna Loa. The images obtained by the two PSPTs are calibrated and made avail- able to the community at the internet ad- dresses http://www.mporzio.astro.it/sola- re/index.html and http://www.rise.hao.u- car.edu. The PSPT concept and proto- type are described in Coulter et al. (1994) and Ermolli et al. (1998) respectively. The current instrument operation is briefly de- scribed by Ermolli et al. (2001), with more complete description available at the OAR web page.