[Leica] performance 11817 versus 11819/11825

[Erwin Puts <imxputs@knoware.nl>]

David wrote in part:
"Second, the Viewfinder just published a fascinating article which
"alleges that the 50 Summicron version produced from 69-79 is in fact the
"definitive performing 50 Summicron, owing to its cost-no-object design,
"later abandoned for the current simpler/cheaper-to-manufacture design.
"Stephen Gandy (cameraquest) had one up for sale on Ebay before the
"article came out, it didn't reach his reserve, so I asked what he
"wanted, and he's now keeping the lens. So what's the deal? Can anyone
"comment on the performance of 11817?

I do have in front of me the official MTF graphs of the Summicron second
generation(11817, from 1969) and the third generation (11819 and 11825,
rfrom 1979).
The MTF graphs of the 11819/11825 show a  marked improvement in the field,
a  higher value for the very important 40 lp/mm, less spherical aberration
and more improvements in the image area when stopped down. Optimum
performance is reached at f/4 with the 11819/11825 and at f5.6 with the
11817.
So technically speaking the current version is optically the better one,
looking at every measurable parameter.
The current lens has six elements, as did the 11817. The double gauss has
two outer elements and a cemented double inner element. The cemented
surfaces are plane in the case of the 11819/11825 and almost plane in the
case of the 11817. It is true that plane surfaces are easier to
manufacture. To infer from this costreduction measure that the earlier
design is of a cost-is-not-an-issue approach is a bit rash. The current one
is certainly not simpler in design or construction. A careful look at the
lens diagrams show an almost identical layout and mounting.
The slightly curved surfaces of the 11817 are more difficult to assemble
and therefor more errorprone.
I have no indication that the 11817 design is of a cost-is-no-objection
philosophy. It could mean that this design is more difficult to build
within required tolerances and that Leitz kept up the tight tolerances and
therefor had to reject a higher proportion of manufactured lenses.
Mechanically and optically the 11817 has no special status and it is a pity
that a new cult/myth is being forged about a lens that has a deservedly
good reputation, but is no match for its successor.
In the article there is a reference to a testreport by Mr Crawley. I have
this report myself and Crawley notes that the 1979version has a higher
internal contrast, is more symmetrical so better for use with extension
tubes and also has better corner definition. So he too concludes that the
1979 design is an improvement on the 1969 version.
He also remarks that the 79version is a bit too crisp for his liking
compared to the 69version, but he also notes that this a philosophical
discussion, not a technical one.


Erwin