Eric, When you focus at any particular distance one third of the depth of field (DOF) is between you and the focused distance, the other two thirds is beyond the focused distance. Therefore when you focus at infinity you squander two thirds of your DOF.
The lens you used has a DOF scale on it. In theory you can use use the whole DOF and improve your chance of adequate sharpness by setting the furthest mark on the DOF scale that corresponds to your current aperture against the most distant point you want to be sharp, or infinity if you will. In practice its always better to use the marks of the next larger aperture, because Japanese DOF scales tend to be basede on smaller print sizes than, say, European DOF scales. This is called using the hyperfocal distance. Some Pentax manual focus lenses had their f8 engraving plus the two DOF marks for f8 coloured red so that you could quickly set up hyperfocal distance for f8. As they say, "f8 and be there". regards, Anthony "Of what use is lens and light to those who lack in mind and sight" (Anon) On 6 June 2011 22:40, Eric Weir <[email protected]> wrote: > > I remain frustrated at my inability to get well-focused shots. Saturday I was > out exploring neighborhoods around the community in which I work and had my > camera along. I came across an adult pickup soccer game on one of the school > playing fields. I stopped and sat in the shade with a group guys who were > taking a break from the game. Then I went out of the field and shot about a > 100 images. > > I was looking forward to seeing the result. It was sunny mid-morning. The > camera's a *ist DS. The lens was an M 135/3.5. ISO was 200. Aperture was > mostly around f11. About half the images were shot at 1/250, half at 1/180. I > kept focus set at infinity. > > I thought surely, at that speed, with that focus, at the distance at which I > was shooting I'd get a few sharp well-composed images. A handful -- less than > five -- are so-so, but not really sharp. The rest are all fuzzy. > > Why can't I get a sharp image? > > Thanks, > ------------------------------------------------------------------------------------------ > Eric Weir > Decatur, GA USA > [email protected] > > -- 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.
