Pentax SMC Pentax-A 645 45mm f/2.8

Pound for pound this is the cheapest way into a properly sharp medium-format wide, and the people who shoot the Pentax 645 have known it for years. On a 6x4.5 frame the 45mm covers roughly the same angle of view as a 28mm on 35mm, which makes it the natural reportage and environmental-portrait lens for the whole platform. It is sharp, it is built like a hand tool, and it sells for a fraction of the equivalent Hasselblad or Mamiya glass. The Pentax 645 system has always undercut its rivals on price, and a wide this good for the money is a big part of why people stay in it.

The "A" in the name is the part that matters in the field. These are the lenses with the green A aperture position that hands stop selection to the body, so a 645, 645N, or 645NII can run aperture priority and proper TTL metering instead of working everything off the ring. SMC is Pentax's Super Multi Coating, and it earns its keep here. Shoot into a low sun or a window and the lens holds contrast where a single-coated wide of the same era would wash out into veiling flare. Stopped to f/8 or f/11 it is bitingly sharp corner to corner across that big negative, which is exactly where you want it for landscape and interiors.

Wide open at f/2.8 there is the field curvature and softening at the extreme edges that almost every fast retrofocus wide carries, plus mild barrel distortion you will notice on straight architectural lines. Stop down a stop or two and the edges snap into line and the distortion stops mattering for anything but copy work. Out-of-focus rendering behind a close subject is smooth and unfussy, neither harsh nor swirly, though backgrounds are not really why you reach for a lens this wide. You buy this glass for the field of view and the resolution.

Who actually uses it: 645 shooters doing documentary work, weddings where you need to put a couple inside a room and show the room, and landscape photographers who want some width without warping everything. The honest weakness is that f/2.8 only buys you so much in a system this heavy. Handheld in dim light you run out of shutter speed before you run out of aperture, and depth of field at 2.8 on this format is shallow enough that focus has to be exact.

It cross-shops against the Mamiya 645 55mm and 45mm and the Pentax 67's wider glass, and it usually wins on price while giving up almost nothing in image quality. If you put a screw-in ND or grad on the 67mm filter thread for a long landscape exposure, meter the scene in Zone Light Meter first and dial the filter's stop loss into the exposure comp so the placement of your shadows survives the filter. For the cost of a single fast 35mm prime you get a wide that holds up across the whole frame, and the secondhand market still hasn't fully caught up to that.