> > "F. Craig Callahan" schrieb: > > > > Norman Chappell wrote: > > > > > It is a means of accurately ensuring the correct point of focus and > > > aperture when a specific depth of field range is required. > The reason Canon > > > don't provide a "shift" capability is that it would basically > defeat the > > > entire purpose that the mode is meant to be used for. > > > > Exactly. If you want more or less DOF change your DEP 1 and DEP > 2 points of > > focus. > > > > You seem to think about DOF a little different than I do. Namely as an > invariaby fix zone, that depends on aperture and focusing distance only. > DOF is a little more complicated, because it also depends on your > definition > what you think is "sharp". Canon thinks a part of the image is "sharp", > when the circle(s) of confusion are smaller than 0.035mm. Now, this is > just Canons definition and not a physical law carved in stone. > And personally, > I find this definition just doesn't meet my expectations. If you > ever enlarge > to 8x12 inch or larger, you'll find that 0.035mm on the neg means 0.28mm > (or more) on the final print. And you'll likely find that doesn't really > look all that sharp. And so what you'll be looking for is not a larger > area that should appear sharp (=more DOF), but you want the same area > to look "sharper". > > Now, in practice, this is not *much* of a difference, but there > still is one. > If I have to guesstimate by choosing appropriate points of focus, > DEP 3 and > DEP 4 so to say, to get DOF (according to my definition, say CoC > size=0.025mm) > from DEP 1 to DEP 2, this negates the concept of DEP mode somewhat, IMHO. > Where do I focus to get this CoC size of 0.025mm if I would get 0.035mm > focusing on DEP 1 and DEP 2? Isn't DEP mode there in order to NOT have to > "guesstimate"? If I wanted to guesstimate (which is not too hard > BTW and I > do it most of the time anyway), I'd avoid DEP mode alltogether and use AV > or M. > > Thomas Bantel
Hi Thomas, You know after reading this thread for a while, I'm wondering how Canon picked .035mm as the standard of acceptable focus. As I recall (hey, I can't help it if my brain is rusty), the liberal value of acceptable CoC is f/1,000 (f=focal length of "normal" lens for film format), depending on the lens design, aperture, image magnification, image size, viewing distance etc. and for the very picky maybe f/1,500. This means that for a 50mm lens .025mm is required for good 8x10 print viewed at a distance 10X (or greater), the focal length (I told you, it's rusty!). Or maybe the .035mm CoC value that Canon picked was arrived at some other way other than as the optimum value for apparent focus for 35mm film. Maybe they considered the lenses in the EOS line at the time DEP was introduced and film speeds in use at the time or maybe they just think 35mm more closely approximates "normal" for 35mm film and that this was an acceptable value. Maybe after selecting the .035mm value and selling a zillion EOS camera bodies they figured that they had better not mess with the way DEP worked, after all look at the uproar caused by the new EOS mount itself and the tremendous amount of bad press Canon got for essentially making the FD mount obsolete overnight. Of course, much of this bad mouthing of the new EOS mount was coming from the soon to be former leader in 35mm SLR cameras! 8^) Regards, Chip Louie * **** ******* *********************************************************** * For list instructions, including unsubscribe, see: * http://www.a1.nl/phomepag/markerink/eos_list.htm ***********************************************************
