Biggles: Yes, the 35/2 is much larger than the Zuiko 40/2. The 40/2 is a pancake lens and the design intent was as a "perfect" normal-ish focal length for press work which, when combined with the size of the OM, made it as close to a Leica RF as you could make an SLR.
If you look at Gary Reese' lens test data
here, you can see that the performance at 2.0 is the achilees heal. However, otherwise it looks like a pretty good to excellent lens:
40mm f/2.0 Zuiko (multi-coated)
OM-1 with mirror lockup
Vignetting = B- @ f/2, A- @ f/2.8, A @ f/4
Distortion = moderate barrel
Aperture Center Corner
f/2 C C
f/2.8 B+ A-
f/4 B+ A-
f/5.6 B+ A-
f/8 A A
f/11 A- A-
f/16 A- B+
Notes: Moderate contrast images with high resolution.
OM-4T with mirror and diaphragm prefire, different sample from above
OM-1 test
Vignetting = B @ f/2, A- @ f/2.8, A thereafter
Distortion = none
Aperture Center Corner
f/2 C+ C-
f/2.8 B+ C
f/4 A- B
f/5.6 B B+
f/8 A- A
f/11 A A
f/16 A A-
Notes: Moderately low contrast in center and low contrast in corners at
f/2; moderate contrast in center and moderately low in corners at f/2.8;
moderately high contrast in center and moderate contrast in corners at
f/4; moderately high contrast in center and corners at f/16; high
contrast in center and corners at f/11; very high contrast in center
and corners at f/8.
Notes:
The tests are from two different samples, so there may be even better or worse samples out there. I would plan on a full CLA by a really good lens tech if I were to purchase one.
Second, my guess is that the pancake design of this lens did not allow for a design to better correct at full aperture... not that I'm an optical engineer. At the time the lens was designed, wide-open performance for DOF control was probably not as important as it is today, or at least performance at moderate apertures had greater priority.
CH Ling (very knowledgeable Olympus user
http://www.accura.com.hk/OM/lenscom.htm) had this to say:
"
40mm F2
High resolution, normal contrast and high color saturation. Bokeh and flare resistance is very good, slight barrel distortion. Amazing performance for a lens that was originally design as a low cost press lens. "
After reading and thinking about this lens some more ... :bang: :bang: :bang:
More info here.