[Leica] Re: w/a M-lens design

[Jeremy Kime <jeremy.kime@bbc.co.uk>]

The question was posed as to why Leica hasn't developed more extreme wide
angle lenses for the M camera if non-retrofocus designs are inherently
easier to design.

I'd suggest that the 21mm S/A was seen as wide enough until they had the
option of buying the remaining Zeiss Hologon lenses. 
The 15mm Super Elmar-R (not Angulon) is the Zeiss design that was referred
to in the earlier post, this along with the 19mm Elmarit is a large lens.

The problem that becomes apparent with lenses like the Hologon is the
natural illumination fall off in the corners neccessitating the
graduated/spot-filters. With retrofocus design this is not an issue as the
exit lens is sufficiently far from the focal plane to eliminate this
problem.
Sadly these retrofocus designs become a problem for the M design because of
their bulk, the fact that they sit so far from the film plane means that
they intrude into the viewfinder area, something which isn't pleasant
either. 
Even the earliest 28mm Elmarit-M was bulky compared to what could be
achieved by previous designs but presumably Leitz pursued that path because
it offered something better than the 28mm (f5.6) Summaron.
The final nail (in the coffin) for non-retrofocus designs came with the M's
metering systems, these effectively precluded these designs as incompatible
with the M5, CL and M6.
Some would doubt whether the 21/2.8 Elmarit improves on the qualities of the
S/A even though it was introduced to allow metering with the Ms.

I have a pair of Canon w/angle lenses which demonstrate the above. The late
'50s 25/3.5 in r/f/c LTM is deep set and an ergonomic joy to use being very
small and deep set, a later (early 70s?)24mm/2.8 SSC (with adapter) performs
better but is far too bulky to realistically use.

In conclusion it remains to be seen whether modern designs can offer
anything which will suit all criteria, a small extreme w/angle lens of the
highest quality which allows M metering without fouling the viewfinder. 
Attempts have been made from the designs created for 'compact cameras', e.g.
the Ricoh 28mm in LTM mount, this is a non-retrofocus design and is both
petite and deep set compared to Leica designs, to continue from my post on
having seen the new 'Voigtlander', this is possible with their new 15mm/4.5
Super Heliar lens too, the design is there, even if the quality may not
be...

Hope this helps,

Jem