Ko.Fe.
Lenses 35/21 Gears 46/20
That lens is a beauty and wonderfully compact. I saw someone with an insanely large Canon DSLR shooting it and it really did just look like an oversized flange. Results are excellent, very sharp and nice rendering, cheap as chips too.
This lens is only I collapsible series lens which reassemble Elmar on exterior.
Optics are different. On DSLRs it only works as close up lens.
I used it where it belongs to. Film RF. Out of all three in this series it is weakest lens.
I-22 is way better on bw and I-50 slightly better for color.
All three have different calculated optics, but share same formula.