IIIf ASA / DIN markings vs. ASA / Weston

[chromatic-aberration]

I've seen some examples of the IIIf that have the film reminder on the advance

knob marked with ASA and DIN speeds, and some that list ASA and Weston film

speeds. Does anyone know if that indicates the intended market of the camera,

or was it something that changed across the board during the production of that

model?

[charles_stobbs3]

Weston used its own film speed rating system for meters they made. In general the rating number was about 80% of the later ASA system.

[Troll]

Tha's very strange, since by the time the IIIF was introduced, the Weston

Rating was obselete. I had one of the very earliest IIIf's, and it was defilitely

ASA and Din. (Now, if i could only get used to calling it ISO!)

[JDMvW]

Modern ISO is technically a combination of the old ASA and the DIN rating (e.g., ISO 100/21o, but even many film retailers only use the old ASA number. Here is a conversion chart that gives equivalent ratings for ASA, DIN and Weston. As you will see it's not linear, exactly.<div></div>

[kelly_flanigan1]

The old 1960's SPIE techinal books have you taking the base 10 log of the ASA; multiplying by 10; then adding 1 to get the DIN number. Thus ASA 100 ia 2*10 +1 =21. ASA 1000 = DIN 31. ASA 10 is 11. ASA 10000 is DIN 41. The DIN system is a log scale; not linear. Since the base 10 log of 2 is about 0.30103 ; one full stop step is often taken as 3 DIN units. Each DIN point is 1/3 stop. 2 DIN units is 2/3 stop' 3 units is one full stop. <BR><BR>Usually 1940's film guides gave weston; GE and asa numbers; and again differences for BW in tungsten lighting numbers too. ASA came out during WW2. Before that Kodak had a "Kodak speed" ; a typical 1930's film had a H & D speed number.

[JDMvW]

1) That was ISO 100/21 degrees, but my effort to make the degree sign didn't work.

 

2) I think your assumption that the film reminder use of a particular scale was an indication of the intended market for that particular camera is generally correct, although there are some variants though time as well when you look at one of the 'catalogues raisonee' for a particular manufacturer.

[kelly_flanigan1]

About 1960 the formal ASA definition for pictorial B&W films changed; most films got higher numbers; sometimes a factor of 2. Thus "conversions" of DIN to ASa and other systems will be different depending on what decade the table was made. Panatomic_x wnet from asa 25 to 40; then back to 32 around 1960; abit a farting around with specs and no change of the emulsion.

[alex_lofquist]

Both versions were available in the US. I had the ASA/DIn on my IIIc and the ASA/Weston on my IIIa.