Modification of Nikkor 3.5/20

[Orio]

Today I have grounded the protruding base part of the Nikkor 3.5/20 to make it mountable on the 5D.
Altough it's always not a good feeling when modifying lenses, this is however a very little surgery that has no consequence on the use of the lens with any Nikon cameras. I already made it on other Nikkor wides. The protruding part (which seems to have no use other than glass protection) makes it impossible to mount these lenses on the 5D.

I then tested the lens on the 5D and I have gotten nice results. The vignetting is moderate and present only at f/3.5
Wide open the lens is barely useable (only if you need to have a shot taken at any cost), but it becomes already acceptable at f/5.6 in the short range (up to 10 meters approximately). Beyond 10 meters, it really needs at least f/8 to deliver an acceptable separation of details.
I can not explain this difference with any other hypothesis that the lens has been planned to give it's best in the short range (from closest focus to 10 meters). This corresponds to interiors use generally, or closeup outdoor shots. As it is generally an opinion that the most advantage for a 20mm lens is for use in indoor narrow places, while for outdoor landscapes a 28mm is usually considered enough, I think that the choice of Nikon engineers can make sense.
My copy of the lens focuses well beyond infinity, I wonder if this is a characteristic of the lens or just a peculiarity of my copy (maybe due to an inaccurate remounting after servicing.
However, getting past this little annoyance is easier with a chipped adaptor, so, no real problem. The performance in the short range is really excellent stopped down, and for me it is enough reason to keep the lens.

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