Some non-ART (in both senses) Sigma lens stuff from the 17-50mm f2.8 OS This lens can be had for well under £200 used and usually under £300 new and whilst not quite in the same division as the ART series and quite a bit slower, I think it is a really good value for a general purpose constant f2.8 for APS-C users and unlike the ART lenses has OS with makes it a good choice for Pocket 4K.