Archived posting to the Leica Users Group, 2012/04/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]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