question about focus and D.O.F...plz help!!

[Rudha]

hi guys i am posting a rough diagram explaining my situation plz follow it....

ok now the really messed up ellipse is the rough area i want the focus to be...the '+' s are the focus points in the viewfinder and i am going to be placing my subject(s) there i want all the three faces to be in focus ....but not much of the background so in short i want the area in focus to be elliptical ....is that even possible.....or is it a matter of increasing D.O.F ......plz help!!!

 

[musicaleCA]

No, not possible. Doable in post processing though. The area that's in focus is a certain distance away from the lens, not an area above, below, or to the sides of the optical axis (the centre of the lens/sensor). The area of focus is a plane perpendicular to the optical axis, not a strange ellipsoid (unless you have a bad lens that goes way OOF at the edges, or worse yet has significant curvature of field).

If you want the background to be OOF, and your subjects to be in-focus, place the background as far away from your subjects as possible, place the camera as close to your subjects as possible, and use as wide/open an aperture as possible. If you need to further de-focus areas of the frame that are still in focus, perhaps because they fell on or near the focal plane, then you will need to blur them in post.

 

[Rudha]

oh ...sorry i always thought of cuboids and ellipsoids .....:blushing:so it's a plane
and thanks for the advice i think i like the distance approach can't wait to try.....may i'll do a little pp

 

[astrostu]

If I'm reading your post correctly, you're photographing 3 people (you say "faces") and you want the "background" to be in focus. That's not a problem, just use a large aperture (small f/#), a relatively long focal length if possible, and have your subjects be some distance from the background.

If you want it as I think musicaleCA interpreted your question - such that only parts of the 3 people are in focus even though their whole bodies will be the same distance from the lens, then yeah, you'll need to do it in post-processing.