Using a smaller sensor or smaller film size gives the photographer greater depth of field in a practical, everyday sense. SMALL-sensor cell phone and smart phones used teeny-tiny, short focal length lenses. My iPhone 4 has a 3.4mm (three point four millimeter focal length!) f/2.8 lens. It has a semi-wide-angle focal length. When it shoots a semi-wide-angle picture, it has HUGE depth of field. When I use my Canon 1.6x camera, I can get the same angle of view with the right lens on the body, but there will be a LOT less depth of field. With my Canon 5D FF body, the same picture angle of view will have only MODERATE depth of field. If I use my Bronica 6x6 camera with its 50mm wide-angle lens, I will get significantly less depth of field. If I set up my 4x5 view camera and my Fujinon 150mm semi-wide, I will get PAPER-THIN depth of field, while still taking a photo that has almost the SAME ANGLE OF VIEW and about the same image size as all the other cameras.
So.. with the iPhone4's teeensy-tiny little sensor, a 3.4mm length lens provides a semi-wide angle of view; for a 1.6x APS-C camera like a Canon EOS 60D a semi-wide is like a 24mm lens.; on 35mm film or digital FF Canon/Nikon 5D-D700-D3 etc.,a semi-wide angle is like my 35mm f/2 Nikkor lens; on the Bronica 6x6 square 120 rollfilm camera, a semi- wide angle lens is like a 50mm f/3.5 Zenzanon PS; when shooting a view camera using 4x5 inch sheet film, a 150mm f/5.6 Fujinon-W is a semi-wide angle focal length. These are pretty rough approximations of focal length. In some formats, DIRECT, millimetewr-for-millimeter equivalents are not available in actual lenses, or are not common. Medium format and 4x5 lenses have BIG gaps in the lens lineups quite often, like 50 to 65mm in the old Bronica system--there is nothing in-between.
I thank you for your iteration, Derrel 
