Obtaining robust photometric redshifts for weak lensing source galaxies is one of the main challenges of cosmological analyses from large scale photometric surveys like the Dark Energy Survey (DES). In this talk I will explain how we can use small scale weak lensing cross-correlations, in particular galaxy-galaxy lensing, to put constraints on the redshift distributions of the weak lensing galaxy samples and to complement other more standard methods. I will present the results we obtained using this technique applied to DES Y1 data. Also, I will describe how using a similar method, but now including CMB lensing cross-correlations, we can exploit small scale information to constrain cosmological parameters, using DES Y1, SPT and Planck data.
