Calculating the height of "J" in Scheimpfluggreenspun.com : LUSENET : Large format photography : One Thread
I have read a copy of the Addendum to Focusing the View Camera by Merkilnger, however I am confused as to how you actually calculate the height of the lens above the plane of sharp focus ( "J" in his diagrams). I appreciate that you measure the height of the lens above the ground, but how do you measure the bit beneath ?????
There is probably a very simple explanation but it has me stumped !!
-- Paul Owen (email@example.com), December 15, 1999
If it's something simple, like a staircase that rises from the ground D ft away up at some angle A, then the amount beneath the ground is just D*tan(A). Otherwise, you guess. :-)
-- James Chow (firstname.lastname@example.org), December 15, 1999.
I think in many common landscape situations you would need surveyor's equipment to get an accurate measure of 'J' to look up the proper tilt. In a fraction of the time I would have the tilt dialed in by using the pragmatic approach of tilt and focus on the ground glass. I think Merklingers books are excellent reference on the subject of DOF and tilt for view cameras, but I leave them at home when I'm in the field using the camera.
-- Gary Frost (email@example.com), December 15, 1999.
Typically, tilts in the field are very small angles. Even if you can calculate it, setting it accurately is a bigger problem. You really have to do it by inspection of the gg. I used a SinarF in the field for a while, and the tilt calculator was useless in many situations, particularly if the camera is mounted high off the ground, say at eye level, with normal or wide angle lenses.
-- Glenn C. Kroeger (firstname.lastname@example.org), December 16, 1999.
I have found, to set the tilt to approx. the right angle, you must first know how far J is beneath the lens. The easiest way to be sure with out making a scaled sketch, visualize where you want your plane of sharp focus to be, then figure how far in front of the camera it intersects through the ground and at what angle, from there it can be solved many ways with some simple geometry. As one thread mentioned above, it usual very small tilt. Make a chart of tilt angles vs. J and you will see, unless the J is very close to the lens, it is a small tilt.
-- Bill Glickman (email@example.com), December 20, 1999.
Thanks very much to all who replied......another silly question answered !! Regards Paul
-- Paul Owen (firstname.lastname@example.org), December 26, 1999.