Otto PETER : 20 December 2002 11:29 wrote: > The triangles > you mention are similar on the object and on the image side of the lens, > the image triangle is just a rotated and scaled down version of the > object triangle. Consider that all windows are in the same object plane, > and hence have the same distance from the film plane (not the same > distance from the camera, of course). > > If, however, you tilt the camera, you will get different sizes for top > and ground level windows (and - if memory serves, and if I did my > calculations were correct - horizontal and vertical scale factors depend > on partly different parameters). You will have great difficulty to > correct this, since there is no simple tool to scale an image with a > gradient to the scale factor, at least I know of none in PS.
Thanks Otto, I should have got a ruler and graph paper out before jumping to my own assumptions! I must confess my comments were based in part on a magazine feature illustrated with two pictures of a church tower one shot on a view camera using a wide angle lens and one tilting a digital camera and correcting in Photoshop. What I remember seeing in those illustrations must then have been distortion caused by the wide angle lens or perhaps was an accurate record of the visual effect of the camera's close viewpoint. The writer of that feature argued that digital and Photoshop was better than using the rising front because it didn't stretch the top part of the tower! I think there should be an accurate way to achieve the correction but I am beginning to feel a little more comfortable with having to stretch the image till it looks about right in Photoshop. Regards Paul Lawrence P.S. - If anyone hears about an 18-20mm shift lens I might just try and trade my Sinar in... --- Outgoing mail is certified Virus Free. Checked by AVG anti-virus system (http://www.grisoft.com). Version: 6.0.427 / Virus Database: 240 - Release Date: 06/12/2002 =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
