DIN <> ASA

Rolf-Werner · 2013-09-15T18:18:10+00:00

Also... jetzt bin ich baff. Hatte gerade meine Ikoflex in der Hand. Da der Belichtungsmesser da drin kaputt ist, hab ich ihn noch nie benutzt und die drehba...

Rolf-Werner

Well... now I’m flabbergasted. I’ve just had my Ikoflex in my hand. As the light meter in it is broken, I’ve never used it and never paid any attention to the rotating scale on the side. And now I’ve suddenly found this: the rotating scale for ISO sensitivity shows DIN and ASA values, side by side. According to this, 24 DIN would be about 60 ASA, 21 DIN about 30 ASA... The light meter gets stuck in the upper range, but it still works up to about two-thirds. After a rough test with my handheld light meter, the DIN scale is correct, but the ASA scale isn’t. Was there ever a different ASA table, or is this a curious bug? I’ve never read anything about it before. Perhaps the Germans weren’t very familiar with the ASA table back in 1956 :-) Rolf

pittyman

Hello Rolf, ? 24 DIN is equivalent to ISO/ASA 400, which is equivalent to 21 DIN ISO 100. ? Best regards, Dirk

Morte

Hi Rolf, There was a change in the DIN-to-ASA conversion ratio at one point; I think that was back in the 1960s. Before that, the calculations were done slightly differently. Take a look at this old conversion table. But that still doesn’t explain the drastic shift you’re seeing. I’d guess it’s a mechanical issue: could something have shifted on the scale? You can find more on the subject in the relevant Wikipedia article, by the way: http://de.wikipedia.org/wiki/ISO sensitivity under the section ‘older systems’.

sputnik

Hello Rolf, ? 24 DIN corresponds to ISO/ASA 400, and 21 DIN corresponds to ISO 100. ? Best regards, Dirk

? ? Hold on Dirk, 24 DIN corresponds to 200 ASA. 400 ASA corresponds to 27 DIN A doubling or halving of the ASA/ISO corresponds to 3 DIN +/-.

pittyman

€ <blockquote class="ipsBlockquote" data-author="pittyman" data-cid="16489" data-time="1379272701"> <div> Hello Rolf, € 24 DIN corresponds to ISO/ASA 400, which is equivalent to 21 DIN ISO 100. € Best regards, Dirk

€ € Hold on Dirk, 24 DIN corresponds to 200 ASA. 400 ASA corresponds to 27 DIN Doubling or halving the ASA/ISO corresponds to 3 DIN +/-. € </div> </blockquote> That’s absolutely correct, Sigfried! That’s what happens when you type faster than you think. € Dirk

Rolf-Werner

Looking at the design, there really shouldn’t be any fault. It consists of a round disc with the values printed on it, and on top of that a rotating disc with two windows. These are, of course, always opposite each other, and the disc underneath might turn accidentally, but the alignment would always be correct. At least, that’s how it appears to be designed. But as the top disc can’t be turned all the way round, a small section underneath remains hidden. Perhaps there really is a misalignment. I don’t think so, though, because you can just about make out the rivet used to secure the scale. Perhaps the scales were fitted incorrectly. Or it really is a ‘glitch’ in the table’s labelling, a curiosity that only occurred in a very small production run. Rolf

Morte

Hi Rolf – I’ve got another rather silly idea. Have another look at the table I posted above. Opposite 21 DIN is 80 (ASA). Opposite 24 is 160. Perhaps over the years the paint on the lettering has simply flaked off – and 80 became 30, and 160 became 60? That’s a rather crude explanation. But sometimes life plays the strangest tricks on you...

Rolf-Werner

Well, unfortunately not :-) The lettering is beautifully engraved and painted black; there’s no chipping at all. I’ll upload a photo:

TiMo

The ASA standard underwent a major revision in 1960 with ASA PH2.5-1960, when the method for determining film speed was refined and the safety factors previously applied to prevent underexposure were abandoned, effectively doubling the nominal speed of many black-and-white negative films. For example, an Ilford HP3 that had been rated at 200 ASA before 1960 was labelled 400 ASA afterwards without any change to the emulsion. Similar changes were applied to the DIN system with DIN 4512:1961-10. from http://en.wikipedia.org/wiki/Film_speed#ASA ? If you double the ASA for your DIN 21 setting, you get ASA 80. That’s almost spot on. Perhaps there was still a small 1/3-stop correction applied to DIN or ASA at the time. If so, that would explain it. In any case, your camera dates from a period when quite a few changes were made to both DIN and ASA.

Rolf-Werner

Ah yes, so that’s how it works… That’s interesting! So, of course, you have to read historical accounts by photographers about emulsions and settings with a completely different perspective. And I’m glad that my light meter, which must date from the same period, already has the modern ASA scale. In any case, it’s always given the right reading; I would have noticed a 2-stop difference. Hmm. Or maybe not? Puzzling... I’ve used it for photos and film – film meaning Double-8 reversal material, colour and black and white, so also material that reacts strongly to incorrect exposure. Photos also mean slides. I’ll have to check that out. But how?

jochen53

Hello Rolf-Werner, I have a Contaflex II, which is also made by Zeiss Ikon. Its light meter also has a scale like that, which doesn’t match today’s specifications.

Rolf-Werner

Hello Rolf-Werner, I have a Contaflex II, which is also made by Zeiss Ikon. Its light meter also has a scale like that, which doesn’t match today’s specifications.

Sorry, I hadn’t realised there was now a second page... So if that was standard for the time, then it’s not a manufacturing fault – I would have been very surprised if it were.