20 mm that can zoom to 40 quicker than changing lenses. similar price to 20mm. Is awesome at 20mm for a non rangefinder wide if you manage to avoid flare. It may perform like a heavy prime 20 with too many elements to resist flare. I have the lens for Canon and Nikon. Nikon version compatible with Nikon F; not a Gtarded gelded lens. I have not scanned negatives to compare so on film it might perform better and match MTF tests (some negstive results may be sensor reflectivety or, may be sensor angle limitations rather than the lens's MTF) it has low distortion and chromatic aberration. May perform better at 40 at closer focus. Durable; might survive self defense use.