DX Coding - Why no speeds below ISO 25?

My cheap F801 goes 1/8000. Really comes in handy during summer but it really gives everything a frozen look.

2F/2F said:

Because they would be 99 percent useless...like DX coding itself is for anything but completely automated point and shoot cameras and/or film shot at box speed. The only possible use would be for those "rigging" cassettes with DX stickers in order to cause their point and shoots to overexpose.

If you want to rate your film at something other than box speed, which must be what you are up to, DX coding is entirely useless anyhow, as you manually override it to do this.

What is it that you are after? How does DX coding benefit you as it is? How would extended low range help you?

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The reason I started looking is that I have a few Pentax P-series bodies (P50 and P30t) which read the film speed from the DX code on the cassette, and do not have manual overrides. They're hardly "completely automated point and shoot cameras", but the ISO setting is one area where they are limited. The film I want to use is some 20+ year old motion picture lab stock, which has a very slow speed- somewhere below ISO 25 - and an effective speed possibly even lower due to its age.

I can code the film for ISO 25 and use it, but the metering will be off. I can manually adjust for it, of course, but it is somewhat of an annoyance to have to consciously adjust for some film but not others... and I run the risk of making exposure mistakes when moving back and forth between this film and "regular" film in more standard ISO ranges that don't need manual exposure offsets.


Once I found out that coding these low DX values was not possible, I was interested to find out the technical reasons why the system was designed this way. Hence, this thread.

Just using a hand held incident meter would be best IMO (but that is almost every situation). I don't think that you should expect those cameras and that film and DX coding to cover your situation to the point of frustration. That film was not made to be shot in a still camera, so that is understandable – not a gross omission by designers.

2F/2F said:

Just using a hand held incident meter would be best IMO (but that is almost every situation). I don't think that you should expect those cameras and that film and DX coding to cover your situation to the point of frustration. That film was not made to be shot in a still camera, so that is understandable – not a gross omission by designers.

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Sure, there are always different and better ways to do things.

I'm not sure that a handheld meter would simplify anything though, as then I would have to manually account for filter factors which the camera's TTL metering already handles.

I could also solve my problem by buying another camera which has a manual ISO control. But doing that would cost way more than the old film, which sort of takes some of the fun out of experimenting.


For my situation, I'm going to have to just manually offset the meter. I already knew that would be the case before I made this thread, which is why I didn't even mention my application.

I've always been interested in the technical side of photography, so this is a question about the history of the standards and specifications more than solving a particular problem.

Diapositivo said:

The reason why those 9 positions were left "undefined" is probably to live room for greater distance between film sensitivities.

Next positions can be: 6400, 8000, 10000, 12800, 16000, 20000, etc;
But they can also be: 6400, 12800, 25600, 51200, 102400, 204800 etc.

Leaving the last positions undefined helps maintaining future use of the standard.

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That's an interesting theory... The only problem I can see is that it would have been a bit painful after the change. Any camera made before the next version of the specification wouldn't give the right ISO for the new films using the new specification... But it would make sense to leave the standard a few spaces that were wide open for anything, in case there was a major breakthrough in film technology.

Steve Smith said:

Some compact cameras do not have contacts in all of the positions and cannot differentiate between some values. I had a Nikon compact camera which would only be correct if the ISO was between 100 and 400.

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I think this is a strong possibility as well. Perhaps the coding was intentionally designed so that more basic cameras wouldn't need the full set of contacts, and the addition of the rest of the unused codes would have broken this ability. Here is a quote from the Wikipedia page:

Wikipedia said:

Most cameras read only part of the code; typically, only the film speed is read, and some cameras aimed at the consumer market only read enough bits to tell apart the most common film speeds. For example 100, 200, 400, and 800 can be detected by reading only S1 and S2 and ground.

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The unanswered question then is "Did the spec have this in mind first?" (which might explain the missing codes)... or did the camera makers just figure this out once the spec was released? (in which case it would not explain the missing codes)

Scheimpflug, I think the standard always had this possibility in mind. In pre-DX world, the ASA-DIN positions varied from camera to camera. My SrT-100x goes from 6 to 6400 but my Canonet goes from 25 to 800.

What is important industrially is not that cameras of today are compatible with codes of tomorrow that are not defined today, but that film of "DX+" of tomorrow will be compatible with "DX" cameras of today. The "blanks" in the standard allow the industry to let's say integrate the ISO 128.000 position without redefining a new coding and knowing that they will be able to sell ISO 100 and ISO 800 film in a backward compatible way.

Fabrizio

Scheimpflug said:

I think this is a strong possibility as well. Perhaps the coding was intentionally designed so that more basic cameras wouldn't need the full set of contacts,
The unanswered question then is "Did the spec have this in mind first?" (which might explain the missing codes)... or did the camera makers just figure this out once the spec was released? (in which case it would not explain the missing codes)

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The system was decided by the "industry" which would have included both film and Camera makers. I would have a fairly high confidence that the camera makers would have requested the design to be made to allow a minimal implementation that covers the 100-200-400 range. (I have at least one point and shoot that has ONLY those three speeds available to use). The film manufactures would have wanted something that they could make with their existing printing system, although the bar codes on the film itself would have required new machinery.

The DX also moved the space where the film type is printed to show through the little window in the camera back. I think it was Fuji that started that idea, but I had one camera that showed the type of Fuji film when I bought it, but started showing a blank space after the DX system came into play.

Recall that the whole reason for this project was to make a 35mm camera as easy to use as a 126 size camera. - 126 and 110 had film speed tabs and 35mm required the user to remember to set the speed.

cmacd123... do the math for ISO 12800 .... f16 at 1/4000 wont cut it. And I said outdoors.

vpwphoto said:

cmacd123... do the math for ISO 12800 .... f16 at 1/4000 wont cut it. And I said outdoors.

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I did'nt say outdoors. ASA 3200 is about the fastest I have seen for sale at the local shop. The canon at 1/4k can probaly handle that anywhere. a copule of the Canon models have the 1/8000 speed, so if you get them to READ that high, you will have to use a lens that closes to f/32 or maybe f/64.

The Canon 2E I have handy by the computer only can be set manually to 6400.

Films start having reciprocity failure with exposures shorter than 1/10,000th second so ISO 12800 does not make sense.

Steve

From Wiki-Thingy:

"ISO 12232:1998 does not specify speeds greater than 10,000. However, the upper limit for Snoise 10,000 is given as 12,500, suggesting that ISO may have envisioned a progression of 12,500, 25,000, 50,000, and 100,000, similar to that from 1250 to 10,000. This is consistent with ASA PH2.12-1961. Canon and Nikon apparently chose to continue an exact power-of-2 progression from the highest previously realized speed, 6400."

In short, "ISO" 12,800 is 1) not "ISO" at all, and 2) digital only, so discussion of it does not belong here!

vpwphoto said:

Pipe dreams... most of the cameras that relied on DX codes didn't have shutters capable of handling these high or low speeds you speak of. Shoot a Nikon F4 would be able to do much with IS) 12800 in sunlight.

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Why would an ISO 12800 film be used in sunlight? Your argument makes no sense, as the point is only to have the camera sense the high speed film, which would be expected to be used under reasonable conditions. Exceeding the capability of the camera to expose the film under wildly inappropriate conditions is a non-issue.

Lost of older cameras' shutters only went up 1/1000th sec., yet their ASA dials went to 3200 or 6400. Clearly, common sense was assumed.

As I have said before, ISO speeds of 25,000 have been obtained in the laboratory with films. At that time, keeping was a problem as these films were hyper sensitive to heat and radiation. OTOH, reciprocity would probably not be a factor since the film could be designed for extremely short shutter speeds thereby mitigating that possible problem.

This work was done with the full knowledge of members of the ISO committee on DX coding. IDK how much it entered into their decisions though.

You see, if you consider fog as a constant density, then the inflection point into the toe represents the "real" speed of the emulsion (the first bit of energy that can be detected by the film) and therefore if it can be amplified properly, then that can become the speed of the emulsion. I have seen several ways of turning the toe portion into a "straight line" portion of the curve in which case the straight line becomes the new shoulder. This has the effect of extreme amplification. When one considers the fact that in an 800 speed emulsion, the toe fraction can then be 1600, by amplification, a gain of 3 stops is at least 12,000 if not greater.

Have fun!

PE

Films start having reciprocity failure with exposures shorter than 1/10,000th second so ISO 12800 does not make sense.

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I don't think reciprocity law failure would be an issue. I can't speak for others, but if I had an ISO 12800 film I'm sure I'd only use it in situations of extremely low light. That's what I'd buy such a film for, anyway.