  BL Lacertae objects (BL Lacs) represent a large fraction (22\%) of gamma-ray
sources in the Third Fermi Large Area Telescope catalog (3FGL). Nearly half of
the BL Lac population remains without a redshift because of their featureless
optical spectra. We aim to increase the number of BL Lacs with a redshift
measurement by using the photometric technique. For this work, we have used 6
Swift-UVOT filters and SDSS g,r,i,z optical filters mounted on the 0.65 m
SARA-CTIO located in Chile and the 1.0 m SARA-ORM in Canary Islands. A sample
of 45 sources was selected from the 3FGL catalog for which photometry was
performed in 10 optical and UV filters to obtain redshift measurements. We
found 3 sources with z>1.3 while reliable upper limits have been derived for 17
sources. The results presented here bring the total number of high-z (z>1.3) BL
Lacs to 29.
