----- Original Message ----- From: "Graydon" Subject: Re: K-7 composition shift question
> > Or maybe I'm just confused, and I'm not sure I can manage ASCII art > diagrams for the first couple floors being right here, nicely parallel > to the sensor, and the top two floors, fifteen floors above those first > two floors, not being (in perspective) parallel, although actually in > parallel unless it's a very funky building. Ok, lets presume that it's a perfect world, because it makes the explanation easier. The walls of the building are perpendicular to the absolutely level ground you are standing on. If the sensor/film is also perpendicular to the ground, it will be parallel to the walls of the building. In this scenario, there will be no keystoning. Keystoning (actually, I think this is when the building appears to be tilted forwards due to over correction, but I'll happily misuse the term because it's one that doesn't see the light of day often enough) arises when the building is taller than the lens in use can capture, and so the camera must be tilted upwards to capture the netire building. As soon as that happens, the building will have the falling over backwards look. The ways to correct it are: back off far enough that you get the entire building in the picture without having to tilt the camera, and then crop out the forground, or move the lens up or film/sensor downwards (with the camera set up square and perpendicular to the ground) or a combination of the two to get the entire building in the picture (generally this is a view camera thing, rarely do shift lenses have enough movement), or take the picture with the camera tilted upwards and correct the image during processing, either with the transform perspective tool in Photoshop (or whatever passes for the same thing in the software you are using) or if you are shooting film, tilt the easel to correct the image (only works if the mage is only slightly skewed due to depth of focus considerations). William Robb -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
