Archived posting to the Leica Users Group, 2003/07/30
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Sorry, Karen, but you are flat out wrong. There is no such thing as accuracy being covered by depth of field. Every lens has a focusing plane where the optical image is at its best, and even in the "cone of light" of the depth of field (based on the standards of the photo industry, that tends to be any part of the cone less than 1/30 of a milimeter) the sharpness falls off as you move away from that optimal plane of focus. And the very FACT that at about 75mm to 90mm SLRs becomes more accurate in focusing than rangefinders is proof. This is a well-known fact, espeically amongst Leica folk, since we've debated this issue for decades (the debate being where the SRL becomes more accurate than the rangefinder). The focusing of a rangefinder camera becomes more accurate at shorter focal lengths. And it has NOTHING to do with depth of field. It has everything to do with basic optics and physics and the very principle of how rangefinders work. The wider the rangefinder base, the more accurate that rangefinder becomes. And the shorter the focal length, the wider the rangefinder base of a given camera becomes in proportion to the focal length. These are just examples I pulled out of thin air, but the principle applies: At 90mm, say the rangefinder base is 100mm. That's nearly a 1:1 relationship. At 50mm, the relationship becomes 2:1, base to focal length. At 24mm that relationship becomes 4:1 base to focal length. It's clearly vastly more accurate in focusing at 24mm than it is at 90mm, because the relative rangefinder base to the focal length is 4 times larger. And it's THAT base that determines focusing accuracy. You can argue that for most people that's not important because they shoot the "f/8 and be there" hyperfocal method. I only use that in riots and other fast-breaking news situations. Because that technique might end up putting the optimal focus plane far away from where I want it. But when you're shooting a 35mm Summilux ASPH vs ANY 35mm SLR with a 35mm lens at 1.4, the rangefinder is going to be clearly superior to the SLR. But at 90mm, the SLR will be more accurate than a rangefinder camera at the same aperture. Basic physics. On Wednesday, July 30, 2003, at 06:49 AM, Karen Nakamura wrote: > So the focusing *accuracy* of a rangefinder is constant, it's just > that that accuracy will be visible with certain lens combinations. Eric Welch Carlsbad, CA http://www.jphotog.com Good judgment comes from experience, and a lot of that comes from bad judgment. - Will Rogers - -- To unsubscribe, see http://mejac.palo-alto.ca.us/leica-users/unsub.html