> >I have one more question: > >You say we would have DOF of 50mm lens instead of 80mm lens. >I won't disagree with that but how is it in practice because >with D60 the 50mm lens image gets not only cropped but also >enlarged after the cropping (assuming you want to have same >size photos). > >The same in film world all the way: > >Photo1: Taken with a 80mm lens, printed to 20*30cm. > >Photo2: Taken with a 50mm lens in the same spot with the > same aperture (f-value). We print it also to 20*30cm > as above. > To get the same framing as above we need to crop it > to a 12.5cm * 18.75cm photo which must have larger > DOF because it is a smaller print taken with a > shorter lens.
Ok. That's true. > Then we need to enlarge it back to 20*30cm which > also makes the DOF (look) shallower than before > enlarging, right? Yes. >Now, the question is if the DOF in Photo2 still is larger >(which I assume it to be)? Yes, it is. >Why? >(My quess: effect (in DOF) of enlarging the photo >was smaller than the effect of a shorter lens (50 vs. 80mm)? Yes, true. >Again, why? DOF relates to hiperfocal distance. Hiperfocal distance increases with the square of focal lenght. When you enlarge photo2 to the magnification of photo1 you only decrease DOF in a proportional (not square) relation to focal ratio. If the 50mm lens in a D30 has a viewing angle equal to a 80mm lens in 135 format then the focal ratio is 1.6. In that case 50mm f/1.4 will be, in the D30, equivalent in composition and DOF to a 80mm f/2.2 in 135 format. (Yo multiply both focal lenght and aperture using the focal ratio). The 50mm will, of course, be f/1.4 in order to do exposure calculations, but the DOF will be equal to the one obtained with a 80mm f/2.2. >regards Vesa Best regards Vicente * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
