Nikon AF Nikkor 20mm f/2.8D

Tight stairwell, a band crammed onto a club stage, the inside of a 1965 Mustang you have to shoot from the driver's seat. A 24mm backs you into the wall and still cannot fit the room. A 20mm pulls the whole scene in while staying short enough to live on the camera instead of in a bag of its own. The f/2.8D is the one that manages both at once: it is tiny for an ultra-wide, roughly the bulk of a fast normal, and it takes ordinary 62mm screw-in filters instead of the bowl-sized front element wider Nikkors demand.

Optically it is a retrofocus design, as any SLR ultra-wide has to be to clear the mirror, and it carries Nikon's Close-Range Correction system: floating elements that hold the corners together as you focus down. That CRC is the reason the 0.25m minimum is a feature rather than a trap. Most fast wides smear at the edges up close; this one stays usable, which is part of why people keep it around. Stopped to f/8 it is genuinely sharp across most of the frame, with the clean, honest, slightly cool rendering Nikon built into the AF-D line. Wide open at f/2.8 the center holds but the corners go soft and point sources grow coma, so night skies and city lights smear at the edges until you close to f/5.6 or so.

The honest weakness is vignetting. Wide open the corners go dark across the whole frame, and it does not fully clear until somewhere around f/16, which is a real consideration if you like skies that read evenly. Distortion is the other one. It is not the tidy barrel curve you can dial out with one slider; it carries a wavy mustache profile that resists simple correction, which is exactly why this lens wants care for architecture and shrugs it off for landscape. Flare exists too. It uses Nikon's Super Integrated multicoating and controls ghosts decently for its class, but put a streetlight or low sun in or near the frame and you will catch some veiling and the occasional ghost, as you would with almost any fast retrofocus wide. Hood it and most of that goes away.

Who buys it: landscape shooters who hike and do not want the 14-24mm f/2.8 hanging off their neck all day, documentary and event people who want one small wide that meters and autofocuses on everything from an F4 to a D850, and film shooters who want a real ultra-wide on an FM or an F100 without paying zoom money. The rival is that 14-24mm, sharper corner to corner, far heavier, far pricier. The other is the older manual 20mm f/3.5 AI-S, smaller still but slower and no autofocus. The f/2.8D sits between them and goes for used-prime money, which is most of its appeal.

That extra stop over the f/3.5 versions is the whole reason to own it, and you will spend it in the dim interiors this lens is built for. Meter wide open at f/2.8 in low light and let Zone Light Meter place your shadows where you want them before you decide whether to stop down at all. The 62mm thread means a normal screw-in grad or ND drops straight on for bright skies, no oversized adapter in the bag.