On Apr 19, 2005, at 7:16 PM, John Celio wrote:
I am trying to work out ho to do hyper focal distance on my *ist D using my
zooms and fixed lenses. Any help would be appreciated.
IN general, if you consider DoF markings on any given Pentax SLR lens, the DoF for the 16x24mm format of the *ist D/DS would be 1-1.5 f/stops greater. That is, whatever is marked for f/8 is what you will net on the D for about f/4.5-5.6.
Godfrey, this makes no sense to me, though I'm sure you're correct. The thing that is confusing me is, since the digital image is simply a crop of what the lens projects on 35mm film, why does the hyperfocal setting change?
You use a shorter focal length lens to achieve the same field of view with the 16x24mm format, for instance: a 35mm lens instead of a 50mm lens for a normal, etc. Consider that the parameters that have the greatest influence on Depth of Field are focus distance and the physical size of the lens opening.
So ... using the appropriate focal lengths for the same field of view, equalize the distance for the same framing coverage ... a 35mm lens on a DS vs a 50mm lens on an MX ... and set the same physical lens opening on both to get the same DoF ... call it 10mm. That means the 35mm lens on the DS is set to f/3.5 and the 50mm lens on the MX is set to f/5, roughly 1.5 stops different.
Godfrey
