Stops on LTM Lenses

[baisao]

<p>First off, I am new to film. Please excuse me if this is a daft question. For the holidays my wife gave me a nice IIIc with an Elmar 90mm f/4 lens. What has me puzzled are how the stops are called out on the lens...but I suspect these will be familiar to you. The stops are: 4, 4.5, 6.3, 9, 12.5, 18, 25, and 36. These do not match modern stops that are powers of the square root of 2: 4, 5.6, 8, 11, 16, 22, 32, 45, etc. Because the modern stops are geometric each 1 stop change increases or decreases the light by 100%. Do the stops on my Elmar follow the same geometric sequence? For example, will a change from f/9 to f/6.3 double the light entering the lens? Thanks in advance, Jim</p>

[mukul_dube]

<p>Yes, Jim, the "old scale" is also a geometric progression.</p>

[zane1664879013]

<p><em>Do the stops on my Elmar follow the same geometric sequence?</em></p>

<p>With the exception of 4 -> 4.5, yes. <a href="../filters-bags-tripods-accessories-forum/00HK0A?start=10">This thread</a> has more info:</p>

<p>Helen Bach: "The official f-numbers for the 'Continental scale' (common before the 1940's) are:<br>

1.1, 1.6, 2.2, 3.3, 4.5, 6.3, 9, 12.5, 18, 25, 36, 50<br>

These are nominally a third-step slower than the closest 'International' whole-step f-numbers that we are now familiar with. No matter whether the lens in question uses the Continental or International scale, the maximum aperture need not be a full step on that scale of course."</p>

[baisao]

<p>Wonderful! I was beginning to get concerned when even my Sekonic L-38 was using the modern sequence; it's only 10 years older than the lens. Thank you both for helping me.</p>

[mukul_dube]

<p>The meter may have been bought ten years before the lens but it is not likely to be ten years older. If you give the serial number of the lens, I or someone else will tell you when it was made.</p>

[winfried_buechsenschuetz1]

<p>Both f-stop sequences are "geometrical". In both sequences any f-stop value is sqrt(2) - the square root of 2 - times the previous value.<br>

BTW on french cameras (with a "modern" sequence" you sometimes find an f-stop value of 23 instead of 22, which is a bit closer to the precise value.<br>

In the early days of photography there were some other (non-geometrical) f-stop values but unless you do large format photography with antique lenses you will never run across such lenses.<br>

 <br>

 </p>

[charles_stobbs3]

- http://en.wikipedia.org/wiki/Waterhouse_stop -

[baisao]

<p>I've noticed that some people are cagey about sharing their serial numbers. Why is this?</p>

<p>The SN on the lens is 675652. The light meter dates to 1960 and I assumed the lens is around 1950. I'm curious to hear how old the lens actually is.</p>

<p>Thanks again,<br>

Jim</p>

 

[mukul_dube]

<p>The serial number puts the lens at 1948. As it has the Continental aperture scale, the distance scale should be metres rather than feet. I was puzzled by this: "my Sekonic L-38 ... [is] only 10 years older than the lens."</p>

[baisao]

<p>Thanks, Mukul. The Sekonic L-38 was only produced in 1960. I just guessed that it was around 10 years older than the lens. Pretty close guess!</p>

<p>Thanks again,<br>

Jim</p>

[mukul_dube]

<p>Older although produced later?</p>

[baisao]

<p>"Older although produced later?" <-- Sorry, cold medicine. :-/</p>

[JDMvW]

<blockquote>

<p>I've noticed that some people are cagey about sharing their serial numbers</p>

</blockquote>

<p>Well, I suppose it may facilitate using the number in forging lenses (from old Soviet versions, whatever). I guess some of us just don't see giving the world more information than it needs to know. Of course, if the lens were 'hot,' then you wouldn't want to give the full number. ;)<br>

In any case, it's not necessary to have the entire number to the last place to determine version and/or age in most cases. "6756xx" would usually do the job.</p>

 

[JDMvW]

<p>Here's an 'Elmar' that has no serial number. COL [chuckling out loud]</p><div></div>

[baisao]

<p>I love the Russians. Give 'em an engraver and some pipe fittings and they can create a Leica that never was. No serial numbers needed :-)<br>

Seriously though, I had wondered if it was because of possible thefts, war trophies, copies...really all sorts of reasons filled my head. Thanks for clarifying.</p>

[astral]

<p>As well as the old 'Continental' (European) aperture values, many classic cameras have old 'Continental' shutter speeds as well. While it is not very difficult to convert a 'modern' meter read-out to these old combinations, it can be inconvenient. My solution is a <strong>Sekonic L-308s </strong>meter which can be set to give read-outs in 1/2 or 1/3rd increments which makes it perfect for use with quirky old cameras and lenses. It also offers incident or reflected metering: highly recommended.</p>

[baisao]

<p>I can’t imagine what Continental shutter speeds would be like. Integers, I hope. ;-)</p>

<p>I am using a Sekonic L-758DR for spot and incident metering. It’s a phenomenal piece of plastic. Just like you were saying with the L-308, I am able to get the L758DR in 1/3rd increments. That’s been really helpful. I really like this meter for when I need to spot meter a spot on a large, distant structure like a dam, building, or a large hill.</p>

<p>I am also using a Sekonic L-38, from 1950, and it gives good results for reflective metering. It’s using International stops and is just a stop slower than the L-758DR. The photos still look properly exposed when ever I’ve used the L-38. Using the closest approximation, I just guess where the aperture should be and read the closest time. It’s a bit of a headache but at $5, I can’t complain. In fact, it’s done pretty well for me.</p>

<p>I suppose I can get good results so long as I am in the ‘ballpark’ on my shutter speeds and apertures.</p>

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<p>Thanks,<br>

Jim</p>