Stellar scintillation is one of the fundamental limitations to the precision of ground-based photometry. This paper examines the problem of the correlation of the scintillation of two close stars at the focus of a large telescope. The derived correlation functions were applied to data from the long-term study of the optical turbulence (OT) in the Northern Caucasus with the MASS (Multi-Aperture Scintillation Sensor) instrument in order to predict the angular correlation of the scintillation at the Sternberg institute 2.5-m telescope currently in construction. A median angular radius of the correlation as large as 20 arcsec was found for the case of Kolmogorov OT. On the basis of the obtained relations we also analyse the impact of correlation in ensemble photometry and conjugate plane photometry. It is shown that a reduction of the scintillation noise by up to 8 times can be achieved when using a crowded ensemble of comparison stars. The calculation of the angular correlation can be applied for any large telescope at a site where the OT vertical profiles are known.