Archived posting to the Leica Users Group, 2005/04/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Ah, that makes sense. Thanks. Scott Henning Wulff wrote: > At 1:21 PM -0400 4/14/05, Scott McLoughlin wrote: > >> Why aren't the framelines in the M's (I have a TTL) very >> accurate for framing? Is there some special technical challenge >> involved? >> >> Scott > > > Rangefinders have two issues which make accurate framing close to > impossible. One is parallax, 'cause you're viewing the subject from a > different point than the lens sees it. Leicas, and most other RFs deal > with this by moving the frame lines towards the lens as the lens is > focussed closer. This is purely a function of the distance, so all > frame lines can move the same amount. > > The other is the fact that a lens, as it's moved away from the body > sees a narrower angle of view. A 50mm lens moves some 4mm or so away > from the body to focus at .7m. So instead of 51mm or so, it's now > acting like a 55mm. I didn't do the math re: the extension, or look up > the actual focal length of Leica lenses, but the ballpark is right. > > Leica has designed the framelines so that at closest focussing > distance, nothing gets cut off if you're shooting slides - the worst > condition. So that defines the narrowest angle of view. If you shoot > negatives at infinity that means that your viewfinder showed a lot > more than you have on your negatives. > > Since you have to move a longer focal length lens a lot more to focus > at the same distance, the longer lenses have the greater error when > shooting at infinity. 21mm lenses will be quite close; 135s have a > _lot_ more on the neg at infinity. > > The above means that medium format cameras, or any other larger format > cameras have a lot more problems, as the 'standard' lens might be an > 80 or 90, and therefore must extend a lot more for closer distances. > That's why they sometimes have the feature that the framelines narrow > and widen as you focus, to more accurately frame the picture. Cameras > like the Koni-Omega had that. It does add complexity and sometimes > caused problems as well as initial expense, but there were less > framelines in those cameras compared with the Leicas as well. There > were some 35's that had that feature as well. > > Leicas of all vintages used the same criteria for frame lines. M3 > frame lines appear to be more accurate, but that was only because it > was designed to focus to 1m (for lenses without eyes), and that meant > that the extension of the lenses, and therefore the constriction of > the angle of view was less. >