just bought 75 Lux

[01af]

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The Summilux-M 75 mm is in fact a 80 mm lens. Not a 80 mm R but a 80 mm focal length. That's what the "50" implies.

This is nonsense. The Summilux-M 75 mm of course is a 75 mm lens, and the Summilux-R 80 mm is an 80 mm lens. As simple as that.

 

 

Make your tests and see.

Please follow your own advice before spreading grotesque misinformation!

 

 

About the lens constructions, it's obvious that a M lens can never have the same construction as a R ...

You're confusing a few things here. An M lens can most certainly be the same design as an R lens of the same focal length, and a few actually are. The reverse is not necessarily true—an R lens cannot always be the same design as an M lens.

 

 

Otherwise what would be the point of them being of different mounts?

To mount them to different types of cameras.

 

 

Nah. Then why does my Summilux-M 75 mm have a '00' instead of '50' ?

Because for some time during the Canadian production period, the focal-length indicator was misinterpreted as a corrective term that would be added to the nominal focal length to give the true focal length. But in fact, the term is meant to replace the nominal focal length's last digit and doesn't add to it. So 75 mm lenses marked '00' are mis-marked and should be marked '50' instead. A hypothetical mark '48', for example, would stand for 74.8 mm ... or '98' on a 90 mm lens means 89.8 mm. By the way, mine is marked '53' which means a true focal length of 75.3 mm.

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[MarkP]

Because for some time during the Canadian production period, the focal-Length Indicator was misinterpreted as a corrective term that would be added to the nominal focal length to give the true focal length. But in fact, the term is meant to replace the nominal focal length's last digit and doesn't add to it. So 75 mm lenses marked '00' are mis-marked and should be marked '50' instead. A hypothetical mark '48', for example, would stand for 74.8 mm ... or '98' on a 90 mm lens means 89.8 mm. By the way, mine is marked '53' which means a true focal length of 75.3 mm.

 

Thanks for clarifying that. I'd not paid much attention to these focal-length indicators (FLIs) present on some of my lenses:

1.4/75 Summilux 391xxxx (v3) FLI 50 is a 75.0mm lens

1.0/50 Noctilux FLI 00 is a 50.0mm lens.

1.4/50 Summilux ASPH/FLE FLI 14 is a 51.4mm lens

3.4/135 APO-Telyt FLI 57 is a 135.7mm lens

None of my many other Leica lenses are marked with FLIs

[pico]

[...] for some time during the Canadian production period, the focal-length indicator was misinterpreted as a corrective term that would be added to the nominal focal length to give the true focal length. But in fact, the term is meant to replace the nominal focal length's last digit and doesn't add to it. So 75 mm lenses marked '00' are mis-marked and should be marked '50' instead. A hypothetical mark '48', for example, would stand for 74.8 mm ... or '98' on a 90 mm lens means 89.8 mm. By the way, mine is marked '53' which means a true focal length of 75.3 mm.

 

I did not know that. Thanks very much! If is not in the FAQ then it should be added.

[01af]

None of my many other Leica lenses are marked with FLIs

Yes—those focal-length indicators traditionally were only present on standard and telephoto lenses but not on wide-angle lenses (one or two exceptions may exist but I'm not aware of any). A couple of years ago, Leica Camera abandoned those indicators altogether, so modern lens models don't have them anymore.

[DigitalHeMan]

Yes—those focal-length indicators traditionally were only present on standard and telephoto lenses but not on wide-angle lenses (one or two exceptions may exist but I'm not aware of any). A couple of years ago, Leica Camera abandoned those indicators altogether, so modern lens models don't have them anymore.

 

 

Yes, I don't have any indicators on any of the wide angles that I have. However my 50 Lux with a serial number of 421xxxxx and a build date last year sometime does still have the indicator.

[01af]

However my Summilux-M 50 Asph with a serial number of 421xxxxx and a build date last year sometime does still have the indicator.

That's why I said, lens models. Those models originally introduced before the indicators' abolition are still carrying them. Later models don't.

 

It seems the abolition happened in 2005. The Summilux-M 50 mm Asph, introduced in 2004, obviously is the latest model that got the focal-length indicator. The Apo-Summicron-M 75 mm Asph, introduced in 2005, has none. So my theory is, all lens models introduced in 2005 or later don't carry focal-length indicators. Does anyone know a counter-example?

[NB23]

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This is nonsense. The Summilux-M 75 mm of course is a 75 mm lens, and the Summilux-R 80 mm is an 80 mm lens. As simple as that.

 

 

 

Please follow your own advice before spreading grotesque misinformation!

 

 

 

You're confusing a few things here. An M lens can most certainly be the same design as an R lens of the same focal length, and a few actually are. The reverse is not necessarily true—an R lens cannot always be the same design as an M lens.

 

 

 

 

 

To mount them to different types of cameras.

 

 

 

Because for some time during the Canadian production period, the focal-length indicator was misinterpreted as a corrective term that would be added to the nominal focal length to give the true focal length. But in fact, the term is meant to replace the nominal focal length's last digit and doesn't add to it. So 75 mm lenses marked '00' are mis-marked and should be marked '50' instead. A hypothetical mark '48', for example, would stand for 74.8 mm ... or '98' on a 90 mm lens means 89.8 mm. By the way, mine is marked '53' which means a true focal length of 75.3 mm.

 

 

I don't pretend to be a professional lens tester nor a professional Leicaist. I'm simply a professional photographer. But I may point that your answers quoting me sound more like Bullsheet then the truth.

 

I have made a comparative shoot-out between my Lux 75 and my Cron 75. There is a difference in Focal length between them. Slight, but present.

This leads to one doubtless conclusion: One of them is not 75mm. I don't want to be Pedantic and Anal about these things that do not interest me at all, to be honest. But still, the 75 lux could well be 80mm or 78.8mm. For Leica to be calling it a 75 is fair enough, especially since there is a 90 not far away. Marketing, of course.

 

Also, your "corrective numbers" explanation doesn't seem to hold well. If a 50mm lux with a "14" suffix is a 51.4mm, then a "50" corrective number on a 75mm lens cannot mean 75mm exactly. At least not in accordance with your explanation. It would mean 80mm. But then again, I do not really care. I'm just pointing out your logic that doesn't seem to hold very well.

 

I'd still like to see a 75mm lux VS 80 lux R focal length comparison, on a M240. That would be interesting. My call is that they are both the same. And if there's a difference between them, it will be the same as between the 75 Cron and the 75 Lux. We're in for a quite funny conclusion, I'm sure.

 

Now at last, as opposed to what you said earlier about the 70cron not having the corrective number, well, you are wrong. Mine certainly does. And it's a later production model as well.

 

I don't know, maybe you could re-check your facts and get back to us? It would certainly be appreciated.

[MarkP]

Interesting because my late production model 75 APO-Summicron does not have a focal length correction number.

[MarkP]

Leica FAQ — Lens white numbers

[01af]

I have made a comparative shoot-out between my Summilux-M 75 and my Apo-Summicron-M 75 mm Asph. There is a difference in focal length between them. Slight, but present. This leads to one doubtless conclusion: One of them is not 75 mm.

The doubtless conclusion it actually leads to is this: Not both of them can be 75 mm.

 

Which is hardly surprising. Two different lens models of the same nominal focal length seldom have the very same actual focal length—there's always a difference of a couple of tenths of millimeters, in some cases even one or two millimeters. And a difference of one millimeter, or even just a half, will make for surprisingly big a difference when comparing the results side by side.

 

So your two 75 mm lenses being slightly different doesn't make one of them an 80 mm lens.

 

 

Also, your "corrective numbers" explanation doesn't seem to hold well. If a 50 mm with a "14" suffix is a 51.4 mm then a "50" corrective number on a 75 mm lens cannot mean 75 mm exactly. At least not in accordance with your explanation.

Sure it can, and it does.

 

Drop the nominal focal length's lowest digit (i. e. the '0' in 50 or the '5' in 75), then replace it with the corrective number. Easy if you eventually drop the misconception that the mathematical operation of addition was involved. In fact, it's just a character replacement.

 

 

Now at last, as opposed to what you said earlier about the Apo-Summicron-M 75 mm Asph not having the corrective number, well, you are wrong. Mine certainly does. [...] maybe you could re-check your facts and get back to us? It would certainly be appreciated.

Your sample of the Apo-Summicron-M 75 mm Asph really has a corrective number? That's odd. So why don't you start checking your facts and tell us what the corrective numbers on your Summilux and Apo-Summicron 75 mm lenses are?

[pop]

Drop the nominal focal length's lowest digit (i. e. the '0' in 50 or the '5' in 75), then replace it with the corrective number.

 

Unless the corrective number is to indicate that the actual length is less than the nominal one.

[DigitalHeMan]

Unless the corrective number is to indicate that the actual length is less than the nominal one.

 

 

I heard that if the number is below 50, then it is added, if it is above 50 it is added to the previous leading digit. For example a 50mm lens with 33 would be 53.3mm, whereas a 50mm lens with 92 would be 49.2mm.

 

However I can't remember my source, so I might be way off....

[Keith (M)]

Reading about these numbers prompted me to look at my Summilux 50mm ASPH and APO-Telyt 135mm (both new in 2014). As can be seen below, the 50mm is engraved with '14', which presumably means a true focal length of 51.4mm. The 135mm is marked '57', so does that mean 135.7 or 137mm?

(both images Leica C in macro-mode).

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[Peter Branch]

Oh dear!

 

Do not believe all you read on the Leica Forum. Most of this thread is a load of old tosh.

 

The 75mm "M" lens and the 80mm "R" lens are NOT the same. They do however share a similar "semi-symmetrical double-gauss" design of 7 elements in 5 groups.

 

As regards designating the focal length on Leica lenses this dates back to the 1930s and has absolutely nothing to do with the US Military. It is only used for lenses of 50mm and longer focal length.

 

Nor does it have anything to do with specifying which shim to use for focus adjustment.

Does anyone really believe that setting the focus to the nearest 0.1mm would be acceptable?

 

It has been reported that the number does have some relevance to the degree of machining required to profile the rangefinder actuating cam on the back of "M" lenses. This seems a reasonable and plausible explanation.

[pico]

Leica FAQ — Lens white numbers

 

It is still a confusing article. It should be rewritten.

[pico]

[... snip helpful stuff ...]

 

Nor does it have anything to do with specifying which shim to use for focus adjustment.

Does anyone really believe that setting the focus to the nearest 0.1mm would be acceptable?

 

How about 0.02mm? Regardless, I accept that shimming would not be good with our relatively short lenses. I was thinking of the aerial lenses for LF that I have worked with. My error.

 

Might there be a relation between the earlier design of the actuating surface and the two-digit number in question? The designs are different as shown in this picture.

[uhoh7]

I also had weak moment yesterday and bought a 75 lux OMG

 

Now it's just a long few days to see just how nice the copy is....

[Lenshacker]

It would make sense that the small number is to be used as the last 2 significant digits of the marked focal length. The "50mm" marking of a lens is only accurate to 1 digit, which is why lens manufacturers used "cm" and not "mm" in the past. So the actual focal length of the lens with a "14" is 51.4, the small number being used to give 3 digits of precision. "75mm" is accurate to two digits, the "57" gives the actual focal length as 75.7. a lens with a "49" would be 74.9mm. The M-Mount made it easier to relax precision required for actual focal length, deviations could be compensated for by indexing the Cam. That was not possible in LTM, actual focal lengths tended to be more consistent. I've taken apart 5 5cm F1.5 Summarits, all were scribed "51.1" internally. Positioning the front/rear cells of a lens relative to each other can be used to set the actual focal length of the lens.

 

I believe getting the actual focal length of the lens accurate to 0.1mm is required for indexing the RF cam of the lens, whether the cam that you see with the 50mm lens or the internal cam of other lenses. With LTM 50mm lenses, the cam was not indexed so the optics had to be positioned to get accuracy in the focal length. Getting the shim to within 0.01mm is good enough for 50mm F1.4 lenses, at least for actual use.

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Hallo,

Look here: Leica M

[ho_co]

It's not a "correction number," and saying "drop the last digit of the nominal focal length and then append the two white numbers" is overcomplicating the matter.

 

The two digits are the last full millimeter and the first tenth of a millimeter of the focal length.

 

If you had a 50 mm lens engraved "17," then the lens would actually be a 51.7 mm.

 

If you had a 70 mm lens engraved "17," then the lens would actually be a 71.7 mm.

 

A 75 mm lens engraved "50" has an actual focal length of 75.0 mm.

 

A 75 mm lens engraved "00" is misengraved, since "00" would indicate a lens of 70.0 mm.

 

The reason for the indicator is that in earlier days different focusing mounts were made for certain focal lengths, and the lens head in question was fitted to the proper mount.

 

All DR Summicrons are 51.4 mm IIRC. That was the design focal length for the dual-range mount, and tolerances weren't allowed. However, non-DR Summicrons made at the same time will indicate variations in actual focal length. Some 51.4 mm lens heads went for dual-range Summicrons, others didn't. No lens head not 51.4 mm in focal length went into a dual-range.

 

The engraving of this actual focal length indicator (not "correction number") has become less necessary as production techniques have improved.

[MarkP]

It's not a "correction number," and saying "drop the last digit of the nominal focal length and then append the two white numbers" is overcomplicating the matter.

 

The two digits are the last full millimeter and the first tenth of a millimeter of the focal length.

 

If you had a 50 mm lens engraved "17," then the lens would actually be a 51.7 mm.

 

If you had a 70 mm lens engraved "17," then the lens would actually be a 71.7 mm.

 

A 75 mm lens engraved "50" has an actual focal length of 75.0 mm.

 

A 75 mm lens engraved "00" is misengraved, since "00" would indicate a lens of 70.0 mm.

 

The reason for the indicator is that in earlier days different focusing mounts were made for certain focal lengths, and the lens head in question was fitted to the proper mount.

 

All DR Summicrons are 51.4 mm IIRC. That was the design focal length for the dual-range mount, and tolerances weren't allowed. However, non-DR Summicrons made at the same time will indicate variations in actual focal length. Some 51.4 mm lens heads went for dual-range Summicrons, others didn't. No lens head not 51.4 mm in focal length went into a dual-range.

 

The engraving of this actual focal length indicator (not "correction number") has become less necessary as production techniques have improved.

 

QED