Survey of the optical variability of compact extragalactic objects. I - The field of 3 C 345

This paper is the first in a series reporting observations of the optical variability of Quasi Stellar Objects at Asiago Observatory. Data is presented for five objects in the field of 3 C 345, namely 3 C 345 itself, NRAO 512, 4 C 38.41, 4 C 39.46 and the compact galaxy Mark 501. Analysis of all the observations available from the literature shows periodicities in 3 C 345 and in NRAO 512.