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Olympus G.Zuiko 20 mm f/3.5 initial test


enricosavazzi

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enricosavazzi

I got a copy of the Olympus G.Zuiko 20 mm f/3.5 after a suggestion by Alex (see this thread). First impression is that this is a small and lightweight lens, easy to carry around. It is designed for half-frame film Olympus Pen cameras, and fits on a Micro 4/3 camera via an adapter. Image circle is large enough to completely avoid vignetting. I am going to put this lens to good use once outdoors shooting season starts again.

 

For my use with a camera that has no filter stack, ordinary adapters do not allow focusing at infinity. I must either add a 3-4 mm window between lens and sensor, or recalibrate the focusing helicoid. I did the latter, but I was also forced to remove several internal mechanical parts at the rear of the lens in order to allow the internal barrel to come about 1-1.5 mm closer to the lens mount. Now the lens actually focuses slightly beyond infinity (my way to recalibrate the helicoid is quick-and-dirty), but this is not a big problem as long as I focus manually. I also had to shorten the length of the focusing ring by about 1 mm to allow the extended focusing range.

 

I did not see any hazing of optical surfaces and no detachments of black paint from a critical internal element. However, I cannot get satisfactory exposure with electronic flash (diffused haze), so I may need to disassemble the lens again and clean all elements. Nonetheless, I managed to take a test image with a 365 nm LED torch (with Nichia 3W chip).

 

The most notable difference with respect to my reference lens (Coastalopt 60 mm Apo) is a very different false color. Both images shot with Baader U. Camera to subject distance and cropping changed, auto exposure (longer by one or two stops with the Olympus lens). Coastalopt at left, Olympus lens at right, both at f/11. There are small focusing differences and I had to crop differently, so DoF is higher in the Olympus picture.

 

post-60-0-35802100-1413479788.jpg post-60-0-91894000-1413479801.jpg

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Enrico, I had similar issue (haze) with my bad copy. The inner element was covered with some oily liquid. Than, when I tired to clean it I noticed that the paint was coming off. It does not look like typical "schneideritis".
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