Which 40 mm lens C T* or CF?
I suppose you mean the 40 mm C lens with T* coating and the later CF version?
The largest improvement of the CF lens is the addition of a floating lensgroup.
Wide angle lenses suffer from less IQ at close range.
To overcome this problem the front lensgroup can be shifted with the CF lens.
This improves IQ dramatically for close range focusing.
The old C lens even has a warning system for the photographer who is about to focus below 0.90 m.
To focus at shorter distance you need to set the focusing ring free with a small control.
Most images are made at larger distances where this problem is not present.
Besides this you may also consider that the C lens is 400 grs heavier than the later CF.
C lenses need filters in B104 size which can be costly and hard to find.
The lens shade for a C lens is essential to prevent flare in back light situations.
This shade is not easy to find as a seperate item.
Still the old C has a charm of its own and is one of my favourite lenses!
Two times 500 CM left with 80 mm CF, right with early non T* 40 mm C lens.
