There are more complications, I think. Of course you can combine
short mount Summicrons and long barrels. The first type of barrels go
to f. 16 and have coarse focus knurl, they are screw mount barrels,
most of them have factory fittet M mount and the red dot. The lenses
also have f. 16. There two types of knurling of the end of the barrel.
The second typ of barrels has f. 22. The knurling is a bit different and
changed often. They ar only M mount lenses, I think. The lenses have
fitted to thes barrals go also to f. 22. There is in my opinion no preset
Summicron originaly with this barrel.
Of course you can combine all detachable Summicron heads with
all barrels, either f. 16 or f. 22. Sometimes you must adjust the barrel,
for the focal length of these Summircon differs often a little bit.
The lense head on the picture I bought last year at Vienna, the barrel
at Stuttgart, the adjustment was made in Hannover, but you can find also
lenses with aperture preset and long barrel, bearing the same serial
number:
90-1.jpg
Regards
Stefan