Active galactic nuclei (AGN) are a source of very high energies. Blazars are a subclass of active galactic nuclei that can be observed in the optical spectral range. The aim of the study is some BL Lacertae type blazars, which are characterized by a non-emission optical spectrum and exhibit brightness variations at all wavelengths. The results of systematical monitoring of selected objects from the CTA (Cherenkov Telescope Array) optical follow up list, started in January 2018 are presented. The observations are carried out with the AZT-8 (D = 70 cm, F = 2.8 m) telescope of the observation station Lisnyky of Taras Shevchenko National University of Kyiv. In 2018 the telescope AZT-8 was included in the list of supporting instruments in the CTA consortium. The AZT-8 equipped with the PL4710-1-BB-E2V CCD (1027×1048 pixels, 13×13 µm/pixel, scale is 0.95 “/pixel, field of view is 16.2 angular minutes) and broadband Johnson/Bessel UBVRI filters. For processing the software Maxim DL was used. During processing accounting of substrate (bias), dark current, flat-field were taken into account. The fluxes of energy from objects of research with the help of standard stars has been turned into visible stellar magnitudes. Light curves for four objects: 1ES 1011+496, PKS 1222+216, 1ES 1426+428, PKS 1510-089 were plotted. Variability of color indexes with time was investigated. In addition, we determined the variability amplitude and tested all these objects for Intraday Variations (IDV), Short (STV) and Long term variability (LTV) where it was possible. A short-term brightness change (STV) with an amplitude of 0.5 to 1 in all filters (UBVRI) of the Johnson/Bessel system for AGN 1ES 1011+496, PKS 1510-089 was determined. For objects 1ES 1426+428 and PKS 1222+216, the brightness variations do not exceed the total error (instrumental and methodical). The total error is ∆Σ ≈ 0.060.1 magnitude.
The Long-Term Optical Variability of the BL Lacertae Object S5 0716+714: Evidence for a Precessing Jet