Most folks do confuse f-stop with aperture, I sure used to. However, they are not the same thing. So you are mistaken here (I have not looked at the Wikipedia article to see if it is correct or not).
I am not going to go through all this again, folks, look in the archives; or better yet, get the formulas and calculate DOF using f-stop and aperture diameter, go out and shot some photos and compare them with your calculations. Then, like me, you will never make that mistake again. -graywolf William Robb wrote: > ----- Original Message ----- > From: "Tom C" > Subject: RE: M85mm f2.0 bokeh > > >> Certainly what you state regarding DOF is true. I believe though the >> writer >> was not making a dogmatic absolute statement of scientific fact. He was >> generalizing. >> >>> As the camera: subject/background ratio wasn't altered, DOF should be >>> SIMILAR for all four lenses. >> I'm pretty sure he knows that actual DOF is not changed by altering the >> subjects distance from the focal plane. That's only moving subjects in >> to, >> out of, or within the range referred to as DOF. I think he means that the >> *perceived* DOF will be *similar*, which is true for lenses close to the >> same focal length used at close to the same aperture. Not the same, but >> similar. > > Depth of field is not subject to changes in focal length if the ratio of > camera to subject to background is not altered, presuming the aperture is a > constant. > What happens if you change focal length is that the angle of view changes, > nothing else. > > If you take a picture with a 35mm lens , then change lenses to a 100mm lens, > and take a picture using the same camera position and aperture, you will > note that the depth of field is identical (presuming a precise aperture > match), but you need to magnify the picture taken with the 35mm lens rather > substantially to match the picture taken with the 100mm lens. > > Wikipedia has a rather extensive article regarding this subject at: > http://en.wikipedia.org/wiki/Depth_of_field > > William Robb > > > -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net
