Old type film speeds

[old bob]

I have acquired a British made Agilux Agimatic rangefinder camera, these were not and are still not expensive but they are well made. I have run a roll of film through and the results were better than expected.
The camera has an extinction meter fitted which allows you to see a set of numbers through a viewer and you set the illuminated number into the calculator discs which in turn gives you a suggested f stop and shutter speed. But first you have to rotate the inner disc and enter the speed of the film that is installed on the camera. I would like to assess the accuracy of this but I do not understand the options of film speeds given. Firstly the camera was made 1956/8 so before the speed change figures of the 1960s.
The disc shows two rows of figures as shown below
Arith, 8-16-32-64-125-250
Log, 21-24-27-30- 33- 36
These figures are on the same scale and appear exactly as above. The camera manual refers to the two series of figures as BS and ASA.

So where I need help is in understanding these numbers and how they relate to modern film speeds. I have searched but have been unable to find a conversion chart from these old ranges to modern film speeds.

Old Bob

 

[CharlesDAMorgan]

The second figures look like DIN - and the first like ASA. However, the DIN results would be considerably faster than the ASA figures, but British Standards used a log system that produced a result about 10 deg lower than the same DIN.

So adjusting for that it would seem the modern figures would roughly be

ASA 8 16 32 64 125 250
DIN 11 14 17 20 23 26

Which looks consistent.

So the ASA looks to be modern ISO.

Hope that helps.

 

[Beemermark]

Usually they do not correspond to any modern film speeds. Extinction meters (as you've probably figured out) were crude but also the state of the art prior to WW II. If you look through old, pre WW-II, developing books a film was given a speed like 5~12 and a sunny sixteen type chart as a starting guess for you to start your developing process. Camera makers also put film speed markings as to what they thought it should be. Yours is post-war but the manufacturer was most likely basing speed on their experience pre-war. Also in this time frame Britain had high import duties on foreign cameras so few were imported. It has looked to me that British makers just glossed up pre-war models to sell into the '60's. Just pretend it's 1938 and start experimenting. Pick a B&W film you like, a developer like D-76 or Ilford ID-11, and take notes.

 

[David Hughes]

The history of film speeds is quite complicated. This is a good article about it and was written in 1960:-

https://www.photomemorabilia.co.uk/Ilford/Film_Speeds_1960.html

NB That was when things got confusing...


Regards, David

 

[Chriscrawfordphoto]

BS film speeds were used in Britain.

ASA speeds were used in the USA and are the same as modern ISO speeds.

DIN speeds were used in Germany.

In addition there were other speeds in the early 20th Century that fell out of use after speeds were finally standardized and every film and exposure meter manufacturer agreed to use the standard systems. These obsolete systems include Weston, GE, and Scheiner (I may have misspelled that one). The Soviet Union had its own speed system too, which was called GOST.

 

[Godfrey]

I have acquired a British made Agilux Agimatic rangefinder camera, these were not and are still not expensive but they are well made. I have run a roll of film through and the results were better than expected.
The camera has an extinction meter fitted which allows you to see a set of numbers through a viewer and you set the illuminated number into the calculator discs which in turn gives you a suggested f stop and shutter speed. But first you have to rotate the inner disc and enter the speed of the film that is installed on the camera. I would like to assess the accuracy of this but I do not understand the options of film speeds given. Firstly the camera was made 1956/8 so before the speed change figures of the 1960s.
The disc shows two rows of figures as shown below
Arith, 8-16-32-64-125-250
Log, 21-24-27-30- 33- 36
These figures are on the same scale and appear exactly as above. The camera manual refers to the two series of figures as BS and ASA.

So where I need help is in understanding these numbers and how they relate to modern film speeds. I have searched but have been unable to find a conversion chart from these old ranges to modern film speeds.

Old Bob

This might prove handy:

from the page https://en.wikipedia.org/wiki/Film_speed

The numbers align between the first and second columns, albeit the provided listing aligns them one number off from the listing you have. It's close enough, I imagine.

G