Back tilt or lens tiltgreenspun.com : LUSENET : Large format photography : One Thread
Having been through Dykinga's new book he seems to advocate rear tilt as the mechanism to get sharpness for near and far objects. I have been using lens tilt to achieve the same effect. Thinking about it - if I use lens tilt then I need a larger image circle to not get vignetting but using rear tilt doesnt have the same restrictions. Is that correct ? My wideangle lens is a 65mm F8 SA which only just covers 5X4 and this may be a better way of making adjustments. I was considering changing my monorail for a field camera with no rear movements and this may make me think again.
-- David Tolcher (email@example.com), December 01, 2001
You are correct in assuming that rear tilts and swings require less image circle than similar movements done with the front standard. Think of this way: The lens projects a cone of light rearward toward the film. When you tilt the lens board, you are re-aiming the cone of light and run the risk of aiming it right off the film, first at the corners of the film (the cone, after all is round) and eventually at the top or sides. When you tilt or swing at the film plane, you are actually intersecting the projected cone by smaller and smaller amounts as you increase the movement. If you view a rectangle (film) from an angle, it will take on the shape of a trapezoid with one dimension getting smaller as you increase the angle at which you are viewing it. I would certainly prefer a camera with no movements at the front over one with no movements at the rear if I had to pick one or the other, but there are occasional needs for movement at both front and/or rear and so would hold out for a something more full featured.
-- Robert A. Zeichner (firstname.lastname@example.org), December 01, 2001.
You are right. But remember of course, rear movements change the geometry of the image unlike front movements. This can be useful. With wide angle lenses, it enlarges foreground objects often producing a dramatic feel to the image. On the other hand, rear tilt means that vertical lines will no longer be parallel, so you have to watch out for the "leaning trees of Pizza"
-- Glenn C. Kroeger (email@example.com), December 01, 2001.
Use a rollfilm back and that lens (same one I have for a 6x9 camera) will cover beautifully with all sorts of bodacious movements!
-- Sandy Sorlien (firstname.lastname@example.org), December 01, 2001.
Keep in mind that, when you achieve near to far focus with rear tilt, then you also compromise managing converging and diverging vertical parallel lines. If you want to retain a vertical ground glass, then you will need the same lens angle of coverage if you adjust for near to far using the front tilt alone or the rear tilt alone. (This assumes that you will be using the front rise/fall to achieve the original framing of the image.)
-- neil poulsen (email@example.com), December 01, 2001.
In response to Neil's suggestion, you can in many cases use rear tilt while maintaining a plumb camera back, simply by planning ahead. In a typical landscape picture you can aim the camera down to avoid excessive sky, then use tilt to return the back to vertical. Now the back is "correct" so trees and buildings don't converge, but focus has also been improved front to back, and since the tilt came at the back it stays in the range of a lens with limited movements. Other situations can be handled in a similar way by thinking it
-- Carl Weese (firstname.lastname@example.org), December 01, 2001.
You can achieve the same result using a combination of front tilt and front fall if you need a plumb film plane. Whatever is easier for the situation: the film/lens relation can be achieved either way.
-- Gary Frost (email@example.com), December 01, 2001.
Thanks to you all - this has been an "a ha" moment for me with my use of the LF camera. I now understand what I am trying to do with movements. Dykinga's book has some good sketches of light cones and angles of front/rear standards combined with your commentary has made this suddenly seem a simple concept.
Brilliant - thanks again
-- David Tolcher (firstname.lastname@example.org), December 01, 2001.