The Sling is a single-strap, quick access bag that swings around for fast shooting without removing the pack. Tenba's exclusive design converts to a lightweight long-lens bag for top-loading your mounted super telephoto lens (up to 300mm f/2.8). A full access back panel opens the main compartment completely, to allow easy setup and cleaning. Think of it as a backpack without the bulk, or a shoulder bag without the strain.
The Small is identical to the Medium size in every way except for size. It will fit a regular sized SLR without the added depth of a vertical grip/booster (actually 2 bodies if necessary), plus lenses, accessories, and a tripod or monopod.