Film Speeds of The Past
The current state of home based emulsion making seems to be able to fairly easily get to ISO speeds as fast as 40 or maybe 50. Some have reported speeds up to 80 and even 100. My current emulsion brew is about 40. This got me to wondering: in today's measurements how did commercial films of the 1920's, 30's and 40's or even earlier compare? I recall hearing that film speed at the time was rated more conservatively than today. I'm specifically interested in black and white films.
My Kodak Tourist folder that I believe my father purchased new in 1947 has an exposure guide on the back listing three Kodak b/w films of the day: Super-XX, Plus-X and Verichrome. (Non-say PAN so I do not know if they were panchromatic films or not.) Going by the "Sunny 16" rule for an average subject in bright daylight, I would guess the speeds of these films as follows:
Super-XX 50 (1/50th @ f/16)
Plus-X 25 (1/25th @ f/16)
(Kodacolor is also listed and I would put that at 25 as well.) Does anyone have any data on other films?
Also, do we have any ideas about the manufacturing process of these b/w films? Were they SRAD's or made by other processes?
If you don't mind doing some cross referencing and calculating, you can download this book from Archive.org:
Most of the popular films and plates available in 1924 are listed with speed numbers that don't correlate well to anything we use today. However, there is also a guide number listed for each product that can be plugged into the exposure tables elsewhere in the text to get sunny 16 exposure values. It's been awhile since I looked any of these up, but the fastest panchromatic emulsion I checked would have been about ISO 25. Most of the panchromatic emulsions were ISO 10 or less.
Here is a chart that compares film speeds. DIN, ASA/ISO, GE & Weston. Should help a little.
Commercial manufactures such as Kodak, Agfa, etc. have long had access to manufacturing methods and chemicals that are not available to the average person. This allowed them to achieve higher film speeds in their emulsions. You are right that in the past films speeds were set more conservatively. This was done to prevent underexposure and insure that the user always got an image. Remember that light meters were not common or very accurate at this time. This practice also allowed products such as Acufine and Diafine to claim speed increases that weren't actually true.
Thanks for the responses everyone. So it would appear that our efforts compare fairly well with the products of the early 20th century. If only I could coat as well as they did then!
Film speeds were
Originally Posted by kb3lms
Super XX 200ASA
Plus X 125ASA
As far as know (I've been wrong more than once) those are the speeds GIVEN by film companies, but yes there was a change in ASA speed at one point. Basically they would rather you OVER expose, than under, and I think that means at one point 100 speed was really 200 speed at today's standards. But I don't know when that cutoff was, and there were different versions of at least plus-x and verichrome so they may have really been 400 and 250 speeds at today's standards.
That's my understanding.
~Stone | Sent w/ iPhone using Tapatalk
The change in ASA speeds arose because they changed the ASA standard.
"The ASA standard underwent a major revision in 1960 with ASA PH2.5-1960, when the method to determine film speed was refined and previously applied safety factors against under-exposure were abandoned, effectively doubling the nominal speed of many black-and-white negative films. For example, an Ilford HP3 that has been rated at 200 ASA before 1960 was labeled 400 ASA afterwards without any change to the emulsion. Similar changes were applied to the DIN system with DIN 4512:1961-10 and the BS system with BS 1380:1963 in the following years."
So then what I said above is correct? (For once...haha)
Originally Posted by MattKing
EDIT: well I know Plus-X is 125 on the NEW standard so does that mean it WAS 64ASA before?
~Stone | Sent w/ iPhone using Tapatalk
The Plus-X speed I am referencing was in 1947. By the Sunny 16 rule according to my Kodak Tourist the speed would have been 25 (1/25th @ F/16) in today's terms per the exposure guide built into the back of the camera.
I have no idea what they gave as the film speed at the time.
In addition to the change in standards, some of the films changed over time as the technology improved, and those changes included changes in sensitivity.
Originally Posted by StoneNYC
In some cases, old films were replaced with new films with different names. In other cases the names didn't change.
Like Vericolour, which went from ASA 125 to ASA 160, and was still called Vericolour.
Although that may have been when it went from Vericolour I to Vericolour II (or was it II to III?).