This Sunday, in celebration of Worldwide Pinhole Photography Day, SoMa’s RayKo PhotoCenter offers photo freaks a chance to see the city from inside a pinhole camera. The Bus Obscura, which at first glance seems like your average tour bus, has been converted into a multiple-aperture camera that creates inimitable scenes of the city we know so well—a view you won't get on MUNI. The bus acts as both the camera and the projector as it reveals a flow of images from the outside. Arrive early: Seats on the bus are first come, first serve. And if the thought of sitting inside a dark bus as dizzying images flicker by makes you nauseous, check out the gallery's exhibition, which also opens Sunday, of innovative pinhole and alternative-method photographers Rebecca Rome and Kath Kreisher.

Pinhole 101:
This basic version of a film camera is photography without a lens. A pinhole camera can be made out of any light-tight object and a tiny pin-sized hole. The image is created as light filters through this tiny aperture onto a piece of photo paper inside the light-tight object. The exposures can last for seconds or hours to create the desired image.

Sunday, Apr. 27, 2008 from 11am-5pm, Bus Obscura Rides from 12pm-3pm, meet the artists from 3pm-5pm, No admission charge, RayKo Photo Center, 428 Third St., S.F., 415-495-3773

Main photo: This slightly terrifying photo was taken by Justin Quinnell. He placed a piece of film in his mouth and—say ahhh—opened wide to shoot the photo. Quinnell’s work will be on display at the side gallery along with more than 70 other winners of the juried pinhole show.