Super Ikonta IV ASA/DIN Conundrum

[DickKenny]

I posted this on another forum, but without eliciting a response. Maybe someone here knows more - or at least better. The original poster was asking if ASA and ISO represented the same speed. And to this, a responder noted:

"ASA American Standard and ISO International Standard are the same Value and are interchangable. ASA (Name) is just not used anymore"

My follow up read:

"Yet here's a thing. The ASA/DIN setting dial on a Super Ikonta Mk1V has two windows with corresponding marks. On this DIN 27 equals 160 ASA; & ASA 400 (approx.) equals DIN 30. I noticed this when loading a roll of Superia X-Tra 400, which of course is labelled as ISO 400/27º. How can this be? Any thoughts anyone."

In fact the ASA 400 is an interpolation. In the Mk IV instruction book they list ASA 320 as the DIN 30 equivalent; which logically it would be if ASA 160 was equal to DIN 27º.

I am old enough to have once known the answer to this little anomaly. Maybe there is someone with a better memory than mine.

[LiamStrain]

That is a bit puzzling...

There are several variables...there were two DIN systems... but as far as I know, both have 27 (or 27/10) = 400.

Also, some old meter/conversion sheets used ASA and Weston values interchangeably (even though they are 1/3 of a stop off). 24° = 160 weston (200 ASA) for instance..

not quite sure... is there a filter factor/high speed flag on that dial anywhere?

[Rod.Klukas]

That is a bit puzzling...

There are several variables...there were two DIN systems... but as far as I know, both have 27 (or 27/10) = 400.

Also, some old meter/conversion sheets used ASA and Weston values interchangeably (even though they are 1/3 of a stop off). 24° = 160 weston (200 ASA) for instance..

not quite sure... is there a filter factor/high speed flag on that dial anywhere?

Hello,
Film speeds changed in the late 1940's after lobbying of Kodak by several photographers including Feininger and Ralph Steiner.
They felt that Kodak used ideal conditions and that under their parameters, the film was rated unnecessarily low.  If you look at 1930's data
Films such as Tri-x were rated at at lower ASA(American Standards Association).  Plus-x was 64ASA, Super XX was 100, and so on.
After the standards were changed, most films speeds doubled.  The data sheets which used to be included with the film all stated the 'film
speed given was for 'an adequate negative', but testing was recommended for a fine negative(one showing more shadow detail).
Many films due the thickness of the emulsion, were, when tested, found to be about 1/2 the new ASA for a 'fine' negative.  Many zone system photographers discovered this after testing.
Rod.Klukas

[DickKenny]

Hello,
Film speeds changed in the late 1940's after lobbying of Kodak by several photographers including Feininger and Ralph Steiner.
They felt that Kodak used ideal conditions and that under their parameters, the film was rated unnecessarily low.  If you look at 1930's data
Films such as Tri-x were rated at at lower ASA(American Standards Association).  Plus-x was 64ASA, Super XX was 100, and so on.
After the standards were changed, most films speeds doubled.
Rod.Klukas

Great answer. Thanks very much. So to sum up - in concert with my ageing sense of logic - I should go with the DIN number, which presumably did not change at the same time. A time obviously after someone in Germany made my Mk IV. Thanks again; and no need to reply if my supposition is correct.

[LiamStrain]

Thanks for clearing that up Rod! Makes perfect sense.