When I had time to look into the flare situation, I tried (fviagruioreus1) cleanings of the lens elements and uses of both the original shade and a makeshift one. Nothing really helped. So, I did what we all might do from time to time: declared a truce with the problem and shelved the project for a rainy day. Recently, with the pandemic, that day arrived.
Entirely separately, I had decided that due to the virus I had plenty of time to test out a lens that Tom Abrahamsson had urged me to buy way back when -- the Cosina Voigtländer 50/3.5 Heliar, the lens that Modern Photography had decreed was the best 50 they had ever tested optically. I wanted to compare it, informally, with my go-to 50, the Apo Aspheric 50/2. Tom had suggested that I buy the version of the Cosina lens in Nikon S mount, so that I could use it on several bodies: Nikon RFs and also SM and M Leicas with appropriate adapters. Tom had named the Nikon S version of this lens “The Mole-Hill Elmar” because of its size and shape. (Perhaps the reader can sense where this story is going.)
Well, I both reacquainted myself with the superb Cosina lens (it is amazingly good), and also decided finally to do something about my Berg Elmar. The Elmar was so clean and nice that surely the fix would be simple if I could get my head around it.
Perhaps I was getting an internal reflection from somewhere in the barrel rather than via the lens elements per se, although when I examined the dismantled elements, it did appear that they flared easily. There were places in the barrel where some of the black flocking had worn off, and especially on one screwhead just behind where the lens elements screwed in. That could have been the culprit. I decided to obtain the correct black paint and carefully touch all this up.
Recently there are new developments in the matter of VERY flat black flocking. I chose a paint where I did not have to buy a large amount, and where there was a domestic supplier. My choice is called “Black 3.0” and advertises itself as “the blackest and mattest acrylic paint on the planet. Unlike other super-black coatings it can be safely applied with nothing more than a brush”. And for me, like other acrylics, it is water soluble and easy to clean up.
Again, from the fact that I am writing about this in Viewfinder, one can correctly surmise that my re-blackening the interior of the lens barrel corrected the problem. So, here are three more images: a recent shot wide-open with the amazing Cosina lens, a side-by-side of the Mole-Hill and Mountain Elmars, and a shot with the Berg Elmar itself at f/6.3.