determining point focused on from bellows extensiongreenspun.com : LUSENET : Large format photography : One Thread |
I can I tell what point I am focused on from my bellows extension. The only lens I have is a 150MM. It appears that I need to know this to use any of the depth of field tables
-- marc fleischman (marcfleischman@msn.com), December 30, 1999
Are you trying to determine focus distance using bellows extension as a yardstick? That can be tough; it's usually easier to measure with a tape measure (at closer distances) or guesstimate (at greater distances) the distance to the portion of the subject that's in focus.Perhaps you could rephrase the question? The "I can I tell" phrase is particularly mysterious. . . .
-- Simon (fourthpres@aol.com), December 31, 1999.
I have answerd my own question. The formula I was looking for is: 1/focal length = (1/object distance) + (1/image distance)object distance is the lens plane to real world object length
image distance is the lens plane to film plane distance (in other words the bellows extension
Thus with a 150mm lens and the bellows extended approximatly 6.3" you are focused at 10'
-- marc fleischman (marcfleischman@msn.com), January 02, 2000.