50/2,8 Planar C, un-numbered distance markings.

No mystery: they're just made that way. Zeiss wasn't exactly known for rational design choices back then (and still aren't: witness the ridiculously cheesy self-destructing soft sticky rubber focus rings on their new $4000 Otus lens line). The unmarked lines in this case actually do make some sense: the distance scale is easier to read at a glance than it would be if marked every three inches. Having the sequence as 3ft, 3.25, 3.5, 3.75, 4, 4.5, 5, might be more annoying then useful: your brain more quickly and easily comprehends the unmarked line between two equal distances than it does literal overcrowded markings. The automated depth-of-field indicators on this lens help compensate for the missing distance numbers.

You probably meant to say "80mm" lens instead of "50mm" lens: the 80mm has the distance scale you describe, the 50mm is different. The 80mm is a general purpose lens designed for spontaneous shooting, so the scale is compromised for that use. Dedicated macro, copy, or cinema lenses often do have the additional complete distance markings because they are used more slowly and/or need to be preset precisely and repeatably.

No mystery: they're just made that way. Zeiss wasn't exactly known for rational design choices back then (and still aren't: witness the ridiculously cheesy self-destructing soft sticky rubber focus rings on their new $4000 Otus lens line). The unmarked lines in this case actually do make some sense: the distance scale is easier to read at a glance than it would be if marked every three inches. Having the sequence as 3ft, 3.25, 3.5, 3.75, 4, 4.5, 5, might be more annoying then useful: your brain more quickly and easily comprehends the unmarked line between two equal distances than it does literal overcrowded markings. The automated depth-of-field indicators on this lens help compensate for the missing distance numbers.

 

You probably meant to say "80mm" lens instead of "50mm" lens: the 80mm has the distance scale you describe, the 50mm is different. The 80mm is a general purpose lens designed for spontaneous shooting, so the scale is compromised for that use. Dedicated macro, copy, or cinema lenses often do have the additional complete distance markings because they are used more slowly and/or need to be preset precisely and repeatably.

You're right... I am talking about about my 80mm f2.8 Planar ..... all the years using 35mm cameras mostly with a "standard" (50mm) lens probably the reason for my mistake. And thank-you for your much appreciated explanation.