That is an excellent point Vesa, I have considered this too, and I was leaving this out because it **really** complicates matters. I have never sat down and run the equations to figure out how depth of field really changes for a given print size, because, to be honest, I don't really care that much...and I probably am not capable of the math, anyway (I switched from engineering school to communications many years ago for these same reasons!)
Intuitively, I would agree with you that photo 2 would have more depth of field than photo one, but I am guessing that it would be by very little, so in my guess it would be practically a wash (which is why I don't pay much attention to the DOF differences). If someone explained why it wasn't a near wash, I might start paying more attention to it. There is one final difference when using a smaller film (or digital) format however...a difference in the amount of diffraction...or, rather, a difference in how much the effects of diffraction are magnified by the increased enlargement that is necessary to make a smaller format capture the same size print as a larger format capture. This is why an 8x10 original can be shot at apertures like f/128 without appearing soft, whereas an equivalent shot on 35mm film is soft at f/16. Generally lens (max) apertures get larger as format gets smaller to make up for this, though with the D30/60 vs. film, the lenses stay the same, though you might say the actual used aperture should be set wider. Then this also affects the depth of field question...all of these considerations, and the fact that depth of field is based on *perception* even in its equations, make it kind of a slippery subject that I don't want to spend the energy understanding analytically...intuition is enough in this area, I think, especially when you have the nearly instant feedback of digital (though I do have to say, a curse on Canon for not including a 1:1 image magnification function on the D30/60...even worse, no magnification on the 1D. The instant feedback is one of the most valuable aspects of digital, but it is compromised by the limited viewing options.) Good luck with your explorations of the DOF question, Vesa. You may want to check out Merklinger's website for lots of theory on DOF, though it might leave you more confused after visiting it. I don't have the bookmark handy, so maybe someone who knows what I am referring to can point us there. Mike Vesa Perala wrote: > > Michael > > 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. > Then we need to enlarge it back to 20*30cm which > also makes the DOF (look) shallower than before > enlarging, right? > > Now, the question is if the DOF in Photo2 still is larger > (which I assume it to be)? > Why? > (My quess: effect (in DOF) of enlarging the photo > was smaller than the effect of a shorter lens (50 vs. 80mm)? > Again, why? > > regards Vesa -- Michael Shupe M.J.Shupe Photography Michigan Tech University www.northernlightsgallery.com * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
