Archived posting to the Leica Users Group, 2012/04/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Actually Phil, Leica went retrofocus long before the M9. It started when they added a TTL meter. WA lenses obstructed the meter, at first physically since the M5 and CL had meter arms in front of the film and from the M6 on the more symmetrical lenses obstruct the light reflected off the shutter curtain white spot to the sensor in the base. Also, if being pedantic, only macro and copy lenses benefit from being fully symmetrical, a fully symmetrical lens would be non-optimum at infinity as well as other normal photographic distances. Even the Hologon isn't completely symmetrical. Looking at my reference the 21mm was retrofocus from 1980, the 24mm always was and the 28mm from 1972. Longer lenses didn't need to be and weren't. There is also no such thing as full retrofocus, merely various degrees. None of the Leica M lenses are anything like as extreme as is necessary for a reflex camera. Compare the 12mm f5.6 Voigtlander with the less wide 13mm f5.6 Nikon for an extreme example! cheers, Frank On 6 Apr, 2012, at 15:35, Phil Forrest wrote: > All of Leica's current lineup of lenses are retrofocus designs due to > the M9 sensor's need for light rays to be as perpendicular as possible. > Their last non-retrofocus lenses were the 21mm and 28mm Elmarits before > the ASPH versions. > > Phil Forrest > > > On Fri, 6 Apr 2012 10:10:08 -0400 > Tim Gray <tgray at 125px.com> wrote: > >> On Apr 06, 2012 at 02:25 PM +0930, Marty Deveney wrote: >>> Inevitable; the ZM "Biogons" are retrofocus lenses, after all. But >>> they display less of the bad sides of symmetrical wides, including >>> vignetting less, and they actually clear the mirror or shutter of >>> most cameras you can use them on. >> >> If you guys are interested, check out pages 9-10 of this pdf by >> Zeiss. They talk a bit about this stuff and how the ZM lenses show >> that there are 'degrees' of design between full symmetric lenses and >> full retrofocus. The ZM biogons (and probably lots of Leica's newer >> lenses) can probably be thought of as a cross between the two, but >> they still share many of the characteristics of symmetric lenses. >> >> http://blogs.zeiss.com/photo/en/wp-content/uploads/2011/12/en_CLB41_Nasse_LensNames_Distagon.pdf> >> >> Also, the bit about entrance and exit pupils on page 11 is >> interesting. I quote: >> >>> With symmetric lenses, the entrance and exit pupils are the same >>> size; this is the case for the old Biogon lenses as well as the >>> Planar types for the rangefinder camera. The Biogon types slightly >>> modified for TTL metering display slight asymmetry of the pupil >>> ratio. >> >> I can confirm that my ZM C-Biogon 21/4.5 exit and entrance pupils are >> pretty much the same size. It does have a larger back focus distance >> than the original and the lens element diagram doesn't look that >> symmetrical (unlike the original), but it has very little distortion, >> has equal sized entrance/exit pupils, Zeiss calls it a Biogon, a lot >> of vignetting, and it has the poor performance of a symmetrical lens >> on many digitals. Does it have some retrofocus 'genes' as Zeiss >> says? Probably. But it if it looks like a duck, quacks like a duck, >> and walks like a duck... >> >> I guess my point is that very few lenses stick with the pure designs >> of the original Biogon, Planar, etc. Also, too, the Zeiss pdf is an >> interesting read. >> >> P.S. - the bit about entrance/exit pupils might give a clue as to why >> Zeiss named the ZM 85/2 a Sonnar. Maybe not - I've never seen one in >> real life, much less looked at the pupil sizes. >> >> _______________________________________________ >> Leica Users Group. >> See http://leica-users.org/mailman/listinfo/lug for more information > > > > -- > philforrest.wordpress.com > gallery.leica-users.org/v/philforrest > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information