The Evolution of Focal Series in LF lenses (anybody know anything about this?)

[c4-contemporary-art]

I was always curious about the logic behind various focal lengths available

and was wondering if anybody knew anything about the logic behind the

establishment of a given geometric series. Here's an example of what I'm

talking about;

 

It occurred to me when first trying to pick lenses for 4x5 use many years ago

that there were at least TWO different main sequences of focal length

available, the dominant one (by dint of completeness of series - and that

containing some of my favourite lenses) is:

 

60mm (58/65 in practice)

90mm

120mm

180mm

240mm

360mm

480mm

720mm

 

You will notice the multiplier in between each length is 1.5, and that every

2nd lens is exactly 2X the focal length of the prior.

 

 

The following lenses were either meant as a separate, competing sequence

to the first or else, were designed as 'filler' lengths.

 

75mm

105mm

135mm

150mm

210mm

300mm

 

Okay - I know perhaps it seems I have too much time on my hands here.. .

and it IS a minor point and unneccessary to shooting, but I was wondering if

anyone (perhaps mssrs Thalmann, Knoppow or Perez?) might have any

info/further thoughts on this.

 

Thanks

Jonathan

[leonard_evens]

What you say about the first series is impossible. If every 2nd lens has twice the focal length of the one two before it, and successive ones have the same ratio, that ratio must be the square root of 2, which is a little over 1.4. In fact, the ratios vary between 4:3 and 3:2. The second series comes closer to constant ratios if you leave out 135. The ratio is close to the square toot of two and each is twice the one two before it.

 

Numerology is always interesting, and perhaps there may be some history here. I hope someone will comment on that. On the other hand, it is possible that any observed numerical rules are more or less accidental.

 

Note that if you start with 60 and multiply by the cube root of 3 successively you get the following series (rounded off)

 

60 76 95 120 151 190 240 302 381 480 605 762

 

With a bit of massaging, one could produce a list which would include almost all your numbers. I don't think that actually explains anything, but it just shows how numerology can produce striking results which don't mean anything in particular.

[dan_fromm2]

For 2x3, the normal lens is 4"; 4x5, 6"; 5x7, 8 1/4"; 8x10, 12"; 11x14, 18".

 

The 240 mm, 360 mm, 480 mm focal you quoted may reflect process lenses that cover 5x7, 8x10, 11x14. Remember that process lenses cover narrower angles than "normal" lenses.

 

Telephotos are typically 2x, 3x, and 4x.

 

Wide angles? Back when, 0.6 x was common. 65 mm for 2x3; 90 mm, 4x5; and so on.

 

As for what people carry around, well, each person has his/her/its own weight limit and ways of seeing.

 

Cheers,

 

Dan

[Troll]

The focal lengths were developed as a result of various film sizes. To answer your question, you'll have to figure out how those many diverse (and strange) formats developed. (Incidentally, some of those metric numbers are just the nearest whole numbers to inches, such as 6"=150mm, etc.)

[c4-contemporary-art]

thanks for the feedback people - but I don't think 'numerology' is here nor

there. Numerology usually trying to project an arbitrary numerical system

on something which doesn't support it (see also: astrology) e.g. numerical

analysis of the talmud or the stock market or something like that, which do

not have a geometric origin. Clearly the designers of lenses , when adding

others to the line, do not start from an arbitrary point. I think it would be

quite reasonable to do a lens of X focal length and then 2X, 3X etc... and

then start filling in the gaps.

 

As for the square root issue - I DO beg to differ. This is a GEOMETRIC series

(linear function, constant multiplier) - not a logarithmic series. 120x1.5 is

exactly 180. 180x1.5 is exacly 270 (okay, okay - I screwed up the actual

series)

[c4-contemporary-art]

Okay I stand corrected. Just thought about it for a second... I was simply

getting confused by the occasional adjacent F.L. being exactly 1.5 the

previous - but didn't follow through with checking all of them. You would be

correct about the sq rt thing. e.g. an aperture series;

 

1, 1.4, 2, 2.8, 4, 5.6, 8, ... etc..

[d._kevin_gibson]

"Clearly the designers of lenses , when adding others to the line, do not start from an arbitrary point."

 

You think that is clearly the case?

 

"I think it would be quite reasonable to do a lens of X focal length and then 2X, 3X etc... and then start filling in the gaps."

 

Why?

 

In many cases there is often nothing at all logical to it (at least in an engineering or mathematical sense) - sometimes (actually, often) it comes down to fashion, marketing decisions or tradition or even what the designer just felt like doing that week...

 

So numerology is probably a pretty good description of trying to make sense of a series of numbers from different manufacturers in different parts of the globe over differeing time periods, especially when different formats were in and out of fashion in those different areas and time periods

 

For example - how did the lingering use of plate film sizes in Japan effect the focal length choices of Fuji or Nikon engineers and managers when those film formats and sizes were long out of use in N America?

 

How did different format popularities between US and Europe effect the decisions of German lens manufacturers?

 

How did the massive use of press cameras - especially in the US - effect choice of certain focal lengths in the range of say Kodak or Wollensak, with perhaps those focal lenthgs lingering on in a range when the initial rationalle for them has long since gone?

 

Just a few of the multitude of variable beyond an engineer deciding what would make a logical series of lenses for his manufacturer.

[bruce watson]

Neither series makes much sense to me. Multipliers of focal lengths don't have a lot of meaning. What does, is multipliers of angle-of-view.

 

What I like are increments of about 15 degrees. So my series ends up being 60mm, 80mm, 110mm, 150mm, 240mm, 360mm. The last one is out, of course, but that's my bellows limit. In angle-of-view (across the 5 inch dimension of the film), that's about 90, 75, 60, 45, 30, and 20 degrees, IIRC. Works great for me. YMMV of course.

[c4-contemporary-art]

Geez. all this heat! Am I making so little sense? Anyway - are not "angles of

view" and focal length exactly interchangeable?? Silly. O f COURSE! The F.L.

places the lens a specific distance away from the film. Seems the angle of

view is pretty much set at that point.

 

Anyway - D.Kevin - to get to your point. I would argue that it's NOT

arbitrary. Let us say, for instance that a first lens is designed. Let's say for

argument's sake that this is a 180mm, a pretty standard lens. Now, the

manufacturer wants to put a SECOND lens on the market. Do you think that

they're going to market a 181 mm lens, and then a 183, and then a 180.5??

God no. That would be ridiculous. Extreme example I know. But it would

seem to me necessary to develop a methodology to flesh out a line. I think

that some sort of numerical series with a logic to it that made sense in

photographic terms might be desirable. And god only knows... we're talking

about germans here, too! LOL). I was just wondering if anyone knew

anything about the intent or history behind these. Guess I should stop being

lazy and pull out the LP Clerc, huh?

 

thanks all.

[john_cremati]

I think in early Photography the factors driving focal lengths was driven by coverage of plate size.. 8x10 being a window pane of glass or a plate....., Second was speed... To take some of these portraits there were very long sittings so they needed fast lenses F 4 to f 8 which at that time translated into big diameter glass.......... These lenses sometimes would have a very narrow field of view..A 16 inch lens in the early days may not cover a full plate .... Enlarging was a pain in the butt so many photographers shot 11x14, sometimes requiring 22 inch lenses..John C.

[ole_tjugen]

In 1910, the standard plate sizes with corresponding plate diagonal were (all in cm): 6x9 (11), 9x12 (15), 12x16 (20), 12x16.5 (20.5), 13x18 (22), 13x21 (24), 18x24 (30), 24x30 (38.5), 30x40 (50).

 

At the same time, Zeiss Tessar (Serie IIb, f:4.5) were sold in the following focal lengths (still in cm): 12, 13.5, 15, 18, 21, 25, 30, 36, 40, 50.

 

Data from Hans Schmidt: "Photographisches Hilfsbuch fuer ernste Arbeit", Berlin 1910.

 

Anyone see a certain correspondence?

[christopher perez]

The lenses a manufacturer chooses to produce may be a simple mixture of history (ie: sunk costs and existing tooling) and marketing (hey, lookee here, we're still sell'n this neat stuff...).

 

As market conditions change, I suspect we'll see more specialized optics being sold at high prices (Schneider's aspherics and new ULF optics come to mind) to satisfy a shrinking, but completely neurotic somewhat monied photo "art" community.

 

For all the other focal lenghts in a manufacturer's line-up, availability will be a simple function of sales volume. If something sells, they'll do whatever needs be done to satisfy demand.