Wide Angle Focusgreenspun.com : LUSENET : Large format photography : One Thread
I came across an article in View Camera March/April 1996 that claims wide angle lenses should be focused using the "focus in" principle. That states that when the subject is further away than the hyperfocal distance at the f-stop in use, the camera should be focused at the hyperfocal distance, and carry the remaining distance to the subject by depth of field for critical sharpness. For example, a 90mm lens on a 4x5 camera set at F32 has a hyperfocal distance of 17 ft., which is where the camera should focus on subjects that are further away than that. The depth of field at that setting would be 8.5 ft to inf. Is this correct?
-- Arthur Gottschalk (ArthurwG@aol.com), October 27, 2001
Just like everything else - it depends. It depends on what you are trying to convey. In general it's not a bad rule. Since wideangle lenses generally include so much foreground infromation, it is disconcerting in most instances when you can literally see the transition from sharp to unsharp. The "infinity" objects, having been diminished in size/importance due to the short focal length of the lens, can ride along on the edge of the depth of field and usually not suffer for it. Also don't forget that "depth of field" is very subjective. All rules are only starting points, and the most effective photos usually break a multitude of "rules".
-- Wayne DeWitt (firstname.lastname@example.org), October 27, 2001.
Arthur: Also, with wide angle lenses, the focus plane is more or less a wide sweeping curve. You will find that if you focus at infinity, the center will be sharp and the edges soft. By "focusing in" you gt the entire image in sharp focus. This may not be as much of a problem with the more modern lenses...I don't really know. I haven't tried and of the newer wide angles, but the older ones required the "focus in" technique.
-- Doug Paramore (Dougmary@alaweb.com), October 27, 2001.
I am just starting to use LF cameras and I seem to recall that using front tilt can greatly increase the range of "in focus". The Scheimpflug (Sp?) Principle offers a way to shift the zone of depth of field to include more parts of the image closer to the camera than a lens at right angles to the ground.
I must check the texts on this myself.
-- RICHARD ILOMAKI (email@example.com), October 28, 2001.
Richard, rear tilt can do this too, but using rear movements also affects perspective rendition asawell as focus distribution.
And Arthur, yes I think you are correct why not do some tests at different focal points and f-stops and report back? I for one am interested to know what the results would be.
-- Ellis Vener Photography (firstname.lastname@example.org), October 28, 2001.
Hi Arthur Why don't you take two test shots? One with the lens focused at its hyperfocal distance and the second one with the lens focused at infinity. You may just be surprised when you compare the results under a loupe! Harry
-- Harry L Martin (email@example.com), October 28, 2001.
To further complicate matters: The View Camera article gave an example of a 90mm lens on 4x5 set to f22 and focused at 200 ft., which would yield "an image that is semi-sharp in the central 30% of the image and ...progressively less sharp toward the periphery..." This is caused by the extreme curvature of the arc of focus, which supposedly closes to 18ft at the edge of the picture. The reson this is not a problem with 35mm and MF cameras is that those lenses already incorporate a focus-in design.
-- Arthur Gottschalk (Arthurwg@aol.com), October 28, 2001.
200 feet to 18 feet ???? And not sharp in the middle to begin with ???? What lens were they using ? Or was it a coke bottle bottom?
-- Michael Mahoney (firstname.lastname@example.org), October 29, 2001.