Archived posting to the Leica Users Group, 1997/11/24
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Subject formerly Re: M6 range finder w/ lens longer than 75mm?? Jacques Bilinski wrote: >The difference between an SLR and a rangefinders w.r.t focusing accuracy is >that when a longer and/or faster lens is mounted on an SLR the focusing >accuracy is increased, but on a rangefinder the focusing accuracy is the >same regardless of which lens is mounted on the camera. > >If for example a Leica can focus to +/-1cm at 2 metres this will be much >more than adequate for any wide angle lens, but will less than adequate for >a 75mm lens at f1,4 where the depth of field is only 6mm. >The depth of field figures come from the j'accuse Leica article at >http://www.caliach.com/paulr/writing/jaccuseleica.html A misplaced decimal in Paul Ross's article in J'Accuse Leica makes for a serious error in his calculation of depth of field. A 75mm lens at f1.4 focused to 2 meters has a depth of field of 6.5 CENTImeters (not 6 millimeters). However I wouldn't get too overconfident with the additional D.O.F. D.O.F. is composed of acceptable focus in front (3.2cm) and in back (3.3cm) of your point of focus. If the Leica can focus to +/-1cm at 2 meters then you can reliably count on a minimum D.O.F. of 2.2cm in front and 2.3cm in back of your subject (from 197.8cm to 202.3cm) or a total minimum D.O.F. of 4.5cm. Of course all of this assumes a standard that many feel is inadequate, an acceptable circle of confusion of .033mm. Paul Ross's article was written in 1995. Has no one caught his error before? Art Art Searle, W2NRA, Lake Grove, NY, USA 20 miles east of Nikon USA, 62 miles east of Leica USA