The S/Ns for the 1.4/50 lens appears to be a myth. All Om Zuiko 1.4/50mm lenses have the same optics. The magic number is 1 mm, not 1.1 mm. At 1 mm, all lenses became MC. At 1.1 mm, the metal for the lens barrel changed to become less costly to produce and lighter by a few grams. The comment to discern SC or MC is true.
When I bought mine, I searched for this on the internet and came to the conclusion that the 1.8 was a better buy, so I bought that. You want a high serial number - over 1,000,000 and either the 'OLYMPUS OM-SYSTEM ZUIKO MC AUTO-S 1:1,8 f=50mm Japan' version or the 'OLYMPUS OM-SYSTEM ZUIKO AUTO-S 50m 1:1,8 made in Japan' version. Though it doesn't say, the second version is also multicoated and supposed to be slightly better. I have used both but couldn't tell the difference.
However the single coated versions and the ones that say F.Zuiko or G.Zuiko or the ones with silver nose are noticeably inferior. I didn't buy the AF confirm adapter for 2 reasons: 1.
I don't think I'd trust it completely for best focus and so I'd still spend the same amount of time focusing. The AF adapter requires manual reprogramming - punching in several camera buttons in a specific order every time you change the OM lens.
If you don't do that, IS uses only one focal length for all your lenses which is sub-optimal. Note that with that adapter the camera thinks a 4/3 lens is attached, so over-riding focal length by manually entering it in the IS menu doesn't work - the adapter reported value takes higher priority. Isscedrbta Driver Xp on this page.
This is the last of Zuiko 50s. It is better overall than all previous versions: better colour, contrast, sharpness. It has no chromatic aberration. It has the most consistent image quality across the frame for each aperture of all lenses. At f1.4 the image is soft with smooth bokeh, so will require postpro to sharpen.
By f2.8 the images sharpens greatly and this is perfect for portraits. By f4 the image is razor sharp. Best apertures for sharpness are 5.6 to 11. This is an ultra-high resolution legacy lens. Images are not flat like digital, but rather have some roundess to them giving the image depth. Coma for this lens is the least among other lenses for its vintage. I think this lens equals my G45 for IQ, and betters it for speed and mechanics.
The mechanics are superb: with a focus smoothness to rival Leica. The best and latest lenses have serial number +1,000,001.
The lens has a cult following, for good reasons. It is an excellent lens for the Sony A7+ and prices are increasing quickly for the +1mm serial numbered lenses. This lens is now my daily lens.