I just found this impressive piece of kit online that's basically a clip that allows you to slide your slr onto either your backpack strap or belt. It looks perfect for urbexing, although it's pretty pricey. Anyone have one/tempted by it?
https://peakdesignltd.com/store/index.php?route=product/product&path=60&product_id=51
https://peakdesignltd.com/store/index.php?route=product/product&path=60&product_id=51