Purpose of small numbers (e.g. 14 or 62) on lens scale?

[Robert Blanko]

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Howdy!

Yesterday I realized that on the lens scale of my Summilux 50 ASPH there is a small „14“ under the yellow „feet“. 🤔

Well, it does not affect my photos and I never saw this so far,  but now I‘m curious what Leica wants to tell the user with said „14“?
 

As you can see on the Leica Website, not all lenses have similar numbers.

The 135 APO Telyt has „62“, the Summilux 50 ASPH now shows „15“ and not „14“ like mine… 🤔

https://de.leica-camera.com/Fotografie/Leica-M/M-Objektive/APO-Telyt-M-1-3,4-135-mm

https://de.leica-camera.com/Fotografie/Leica-M/M-Objektive/Summilux-M-1-1,4-50-mm-ASPH

Any idea?

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[wda]

From memory, this shows the actual focal length, or rather, the actual last digits. Instead of 50 mm, yours measured at 51.4 mm. Marginally longer than nominal.

For most purposes, this is of academic interest only. Your rangefinder or EVF takes no notice of such information.

[a.noctilux]

Those are measured real focal length of the lens expressed in 1/10 of millimeter, inscribed only last two digits as xx 1/10mm.

When manufacturing (maybe not now) many people involved, optical cell at another place (or with other technician) than mechanical parts  to be assembled so these numbers are incribed for matching elements together, then tested.

In older lens with separable optical/focus modul, we can see these number inside each element, always matching for proper functioning.

On Summicron 50mm of 1960's we have 16/19/22 = 51.6mm, 51.9mm, 52.2mm

 

As side note on DR Summicron 50mm, nothing of these number on the lens mount.

I had explanation, those DR are all 51.9mm measured  (selected from the batch), so no need to inscribe the number.

If we unscrew the optical cell, we would see engraved the measured '51,9' on the optical cell.

 

Rigid Summicron 50mm do have those number as 16/19/22 as said.

Tradition can have something to do with these small wonder numbers.

Just had a look at my three Summilux 50mm, of different period : they have these number '13' for the oldest, '16' on the newer (1990's), and the newest has also '16',

strange

...

On many 50mm Noctilux 1.0,  I see '00' meaning those are real 50.0mm lenses

I see these only on lenses from 50mm or longer focal lengths.

Edited August 21, 2021 by a.noctilux

[mmradman]

1 hour ago, wda said:

From memory, this shows the actual focal length, or rather, the actual last digits. Instead of 50 mm, yours measured at 51.4 mm. Marginally longer than nominal.

For most purposes, this is of academic interest only. Your rangefinder or EVF takes no notice of such information.

I could be wrong but my understanding is that the true FL for 50mm lens is 51.6mm. As it happens my Summilux 50mm has 16 engraved on the distance scale which makes is 51.6mm, I would not be bothered if any other value was engraved.

[a.noctilux]

2 minutes ago, mmradman said:

I could be wrong but my understanding is that the true FL for 50mm lens is 51.6mm. As it happens my Summilux 50mm has 16 engraved on the distance scale which makes is 51.6mm, I would not be bothered if any other value was engraved.

Mladen, as I wrote, the real measured focal length is engraved on nominal 50mm lenses.

 

I have a chart where 50mm Summilux can have one of these:

10, 11, 13, 14, 16, 17, 19, 20, 22 so variable from 51.0mm to 52.2mm measured (real ! )

[Jean-Michel]

And, the nominal focal length is only valid for the lens focused at infinity. For objects closer than 'infinity' the focal length is, typically, longer.

The formula:

(1/object distance) + (1/distance from lens to image) = (1/focal length)

(1/infinity) + (1/50 mm) = (1/f)  Since 1/infinity is close to zero, we get (0) + (1/50) = 1/50, therefore the focal length is 50 mm

Focusing to a shorter distance typically means that the lens to image distance is greater, therefore making for a different calculated focal length. It is pretty much irrelevant for photography, but can be an issue in filming or videography where you can get lens 'breathing' when the focus changes from, say, one actor's face to another one's.