Of apertures and a 1893 world fair album

You know Le Corbusier? If not: he's one of the most important architects of the 20th century. That's short enough, isn't it? And if you want to know more, just Google.
What about him? I have been asked by the author of a book on Le Corbusier to say some sensible things about the first camera that our famous architect bought. Guess what brand it was! Some questions related to the apertures of Kodak box cameras from the 1900 period. I have a nice library of photo-history books and journals, but in it I could not find what the apertures on these cameras are. So I had to go back to the basics, meaning that I had to measure the diameter of the stops and the focal length of the cameras. Of course you all know that you can calculate the aperture value with the simple formula a=f/d, where a is aperture value, f is focus and d is diameter of the opening. To make a long story short, here's what I found:

My measuring tool is a simple caliper, nothing digital, no laserbeam. So give or take a millimeter in the focal length and + or - 0,2 in the diameter of the stop. The results stay much the same.
The largest stop on these cameras is about f/15, very close to the value we are used to: f/16.
The smallest stop is about f/30, also very close to the better known f/32.
There is one stop in between and it wouldn't be foolish to expect that this was f/22 or f/21. But it is not. The middle stop is f/18, about halfway between f/15 and f/21. Rather confusing if you are used to the standard range where every stop is equal to half the light passing through the lens. That made combining shutter speeds (1/30 - 1/60 - 1/125 - 1/250 etc) and apertures simple in the days not so long ago, when your camera was not a computer.

But in the days of the No. 2 Bull's-Eye or No. 2 Falcon, the stops on these cameras were not used to combine with shutter speeds for artistic effect. They were meant to accomodate to light conditions. Standard condition was bright sunny weather. Everything else was some sort of a problem. Let's see what the No. 2 Flexo instruction booklet say about this. (They all say the same.)

The largest stop f/15 is for all ordinary work in sunny conditions.
The middle stop of f/18 lets in slightly less light in very bright conditions.
The smallest stop f/30 is for Time exposures only, out doors or in doors.

There is some more info in the booklet that confirms the calculation of the middle stop as being f/18 and the smallest as being f/30.
When the middle stop was used, one had to add one half of the exposure time. That is equal to one half stop.
With the smallest stop f/30 one had to give four times the exposure time. This is equal to two stops. Example:
f/15 with 2 seconds
f/21 with 4 seconds
f/30 with 8 seconds

Apart from the question about the apertures, there was a question about film speed in the early 20th century. There was not a global system to indicate the speed in those days, but several methods. Kodak used a very indistinct system with descriptions like "slow" of "fast" films. Quite a difference compared to our ISO system or the ASA and DIN system of my youth.

No. 2 Falcon, one of the cameras that was used to
calculate the aperture range of early Kodaks.

Do you remember the old Sunny 16 rule? I quote from wikipedia: The basic rule is, "On a sunny day set aperture to f/16 and shutter speed to the [reciprocal of the] ISO film speed [or ISO setting] for a subject in direct sunlight." For example: On a sunny day and with ISO 100 film / setting in the camera, one sets the aperture to f/16 and the shutter speed to 1/100 or 1/125 second (on some cameras 1/125 second is the available setting nearest to 1/100 second).
Knowing that the largest stop in the early Kodak boxes is f/16, one can calculate the speed of the film if one knows the speed of the shutter. I have not the means to measure the shutter speed, but my guess would be between 1/25 and 1/60 of a second. Following the Sunny 16 rule, this would mean that the speed of the film woud be around 25 to 60 ISO.
If I follow the instructions in the booklet and give 20 seconds exposure with f/15 in door on a cloudy dull day (like today), I can calculate that the speed must be around 40 ISO. We will leave it to that for now.

Something quite different is the photo album I stumbled upon while browsing through eBay. It is a Columbian Exposition album, dated 1893, with cabinet and CDV portraits and tintypes. I assume it was sold at the world fair as a souvenir. I have no idea of its value or rarity, but I would want it because of its beauty. Be quick if you want it. Only 14 hours to go, no bids yet, starting price is $ 150.