> > Perhaps someone has already done the math, or the experimentation, and > can just give me the answers. > > Scott's pictures of his Nishiki inspired me to shoot some of my > mongrel legnano. I rode it to lunch today, and on the way back to the > office was getting some shots of it with some lupin by the side of the > trail. > > I didn't have quite as much depth of field as I'd like, so I decided > to try zooming way out and then just cropping. Smaller sensor, shorter > lens, more depth of field. If the equation is linear, I should get the > same DOF by downresing (downrezzing?) a longer lens over the whole > sensor, as I would using a shorter lens and cropping. > > This would also mean that a K20 would have a lot less DOF than my K100 > at the same focal length, assuming that they were blown up large > enough that the sensor resolution became a factor. > > So, if I'm willing to trade resolution for depth of field, am I better > off using a wider angle lens and cropping (my intuition says yes), or > do I get the same benefit by just combining pixels (which would also > reduce noise) for a larger circle of confusion? >
To calculate the nearest (dn) and furthest (df) points in focus use the following formulae: dn = U * F^2 / [F^2 + (U * c * f)] df = U * F^2 / [F^2 - (U * c * f)] where c = circle of confusion U = subject distance F = focal length f = f-number To calculate the circle of confusion c = (v * D) / (1000 * S) where v = film format / image size D = viewing distance S = print size Source: The Professional Guide to Photo Data, 3rd edition, by Richard Platt. Very easy with a spreadsheet. Bob -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
