DX Coding, Exposure tolerance

abruzzi · Sep 16, 2018

I was looking at the DX coding chart today, and I thought its interesting what the second row is for. It records the number of exposures on the roll, and the”exposure tolerance.” I pulled two rolls of Fuji I had—Superia X-TRA 400 and Velvia 50. The C41 film has the code for +3/-1 and the slide film has the code for +/-(1/2), which seems about right. Which of course begs the question, do any cameras actually read the exposure tolerance codes, and if so, what do they do with it? (I looked at the only DX enabled camera I have, the Nikon F4, and it only has a single row of sensors.)

AgX · Sep 16, 2018

I assume that tolerance information only makes sense with complex metering systems.

EdoNork · Sep 16, 2018

Maybe used by the Minilabs equipment?

abruzzi · Sep 16, 2018

yeah, I was just curious if and how the information was used. I was thinking that a matrix system could adjust by in inferring dynamic range, though that not really what the data indicates.

darkroommike · Sep 16, 2018

EdoNork said:
Maybe used by the Minilabs equipment?

Having worked in a mini-lab I'll say no. Unlike APS, with 35mm, the cartridge is discarded before the roll is processed or printed, and not reattached after processing.

MattKing · Sep 16, 2018

It would tell the camera that slide film is present.

darkroommike · Sep 16, 2018

MattKing said:
It would tell the camera that slide film is present.

Yeah but only if your camera supports the second row of DX pins. I just checked the manual on the F6 and it doesn't mention anything about that DX feature. Does anyone have a camera example that has two rows of DX pins in the body?

darkroommike · Sep 16, 2018

darkroommike said:
Having worked in a mini-lab I'll say no. Unlike APS, with 35mm, the cartridge is discarded before the roll is processed or printed, and not reattached after processing.

I am going to quote myself, the DX cartridge code was not used in mini-labs, and very few mini-lab printing machines supported the DX edge code. In any case that's ancient history.

abruzzi · Sep 16, 2018

The other thought I had was maybe for later consumer cameras that implemented “exposure compensation” with buttons and an LCD, they might have read the code, and limited how much exposure compensation you could dial in based on the DX information.

Or maybe it was never actually implemented. I doubt I’ll ever see a camera that uses it, I’m mostly just curious if and how it was used.

pentaxuser · Sep 16, 2018

It is a good question. There has to have been a reason for it but for what that could be used and by what means?

pentaxuser

Agulliver · Sep 17, 2018

In theory a camera or lab could use the information....but I'm unsure if it was ever widely implemented. Possibly something that the DX code designers intended but which was rarely used in real life.

abruzzi · Mar 9, 2019

I'm necro'ing my own thread, but I though I'd add a tiny bit of information. I recently bought a Pentax MZ-S, and lo and behold it has pins to read the second row from the cassette. If I'm looking at it right, it has a row 2 ground pin and T1 and T2 pins for exposure tolerance, but no pins for L1, L2, and L3 for reading film length. I read through the entire manual, and couldn't find any reference to differing behavior when the tolerance vale is set. I saw one review that offhanded makes the claim that it take exposure tolerance into account, but otherwise the internet is completely laking in information on the feature on this camera.

M-88 · Mar 9, 2019

abruzzi said:
I'm necro'ing my own thread, but I though I'd add a tiny bit of information. I recently bought a Pentax MZ-S, and lo and behold it has pins to read the second row from the cassette. If I'm looking at it right, it has a row 2 ground pin and T1 and T2 pins for exposure tolerance, but no pins for L1, L2, and L3 for reading film length. I read through the entire manual, and couldn't find any reference to differing behavior when the tolerance vale is set. I saw one review that offhanded makes the claim that it take exposure tolerance into account, but otherwise the internet is completely laking in information on the feature on this camera.

So, alright, let's say that the camera can read the second row of DX coding and it can see the exposure tolerance/latitude of the film, how will it use it? I mean, if the latitude is +1/-1 stop, will it preven the user from exposure compensation larger than that? Can't you set +2/-2 stops?

pentaxuser · Mar 9, 2019

'd really like to see an explanation from a source where the person or the link is connected to the manufacture of the cassettes or pins in the camera. It seems incredible that depending on the scene being metered the camera's meter "communicates" to the pins and tells them to rate that film as other than or at box speed for each frame being exposed?

pentaxuser

ic-racer · Mar 9, 2019

darkroommike said:
Yeah but only if your camera supports the second row of DX pins. I just checked the manual on the F6 and it doesn't mention anything about that DX feature. Does anyone have a camera example that has two rows of DX pins in the body?

Yes, this should be the title of the thread. I'm curious too.

One reasonable use for the 'exposure tolerance' information would be to extend the threshold for the generic "LOW LIGHT" warning on some cameras.

On the other end of the spectrum, some cameras may only have shutters that go to 1/500 or 1/1000 and, if over-exposure tolerance were sensed by DX, the camera could extend the threshold for showing a "TOO MUCH LIGHT" warning.

I'd think films like XP-2, TMY and TMZ would have large values for that DX variable.

I can't imagine how a film processing machine would use that information. Maybe someone can post a picture of a film processing machine with two rows of DX contacts.

Chan Tran · Mar 9, 2019

EdoNork said:
Maybe used by the Minilabs equipment?

I am quite sure minilab don't use it.

Chan Tran · Mar 9, 2019

darkroommike said:
Having worked in a mini-lab I'll say no. Unlike APS, with 35mm, the cartridge is discarded before the roll is processed or printed, and not reattached after processing.

In the minilab I managed back in the early 80's, we pulled the film leader out of the cassette. Attach it to the plastic leader card and put it in the C41 processor. The processor will pull the film out into the machine and cut the film off at the end. I know the machine didn't use the DX code but it;s possible to read the code and then send the info along. However, you don't process C41 any different regardless of film speed, or exposure latitude. During printing the printer would try to measure density and color balance from the negative. Latitude information is not useful.
Latitude information can be useful in the camera though. But of course I don't know of any camera that use that information.

M-88 · Mar 9, 2019

Perhaps that was a redundant feature which was supposed to be used somewhere somehow, but they dropped the idea in the end.

Bill Burk · Mar 9, 2019

ic-racer said:
Yes, this should be the title of the thread. I'm curious too.

One reasonable use for the 'exposure tolerance' information would be to extend the threshold for the generic "LOW LIGHT" warning on some cameras.

On the other end of the spectrum, some cameras may only have shutters that go to 1/500 or 1/1000 and, if over-exposure tolerance were sensed by DX, the camera could extend the threshold for showing a "TOO MUCH LIGHT" warning.

I'd think films like XP-2, TMY and TMZ would have large values for that DX variable.

I can't imagine how a film processing machine would use that information. Maybe someone can post a picture of a film processing machine with two rows of DX contacts.

I think those would be good ways to use it, to extend the low light warning and overexposure warning. But maybe even Program mode, at the low end, could use slightly faster shutter speed knowing it's in tolerance. Not aware of any cameras that did that but it would have been fun to design cameras that did that.

pentaxuser · Mar 10, 2019

Not wishing to act as the "wise-guy" but I am still unsure what the exposure tolerance in DX coding can actually do or does in reality.

Can someone sum up what it does and what the camera needs to have in it to enable it to do it?

Thanks

pentaxuser

darkroommike · Mar 10, 2019

pentaxuser said:
Not wishing to act as the "wise-guy" but I am still unsure what the exposure tolerance in DX coding can actually do or does in reality.

Can someone sum up what it does and what the camera needs to have in it to enable it to do it?

Thanks

pentaxuser

Not sure how to enable it but consider this, most negative films are quite tolerant to overexposure so it might be useful to tell the camera to bias exposure in that direction. Vice versa, color slide films, while less tolerant overall can handle a bit of underexposure better than over exposure.

pentaxuser · Mar 10, 2019

Thanks darkroommike but how does the exposure tolerance coding send that message to bias towards overexposure in the case of a negative film to the camera? What does the coding line on the cassette learn from the meter that decides an overexposure is required and under what circumstances or is it the case that this line of coding effectively tells the camera to overexpose all shots in the case of negative film. In which case if I set the ISO speed on my camera to say the box speed of 400 does the camera automatically via the exposure tolerance code on the cassette actually set the speed to say 200? If this were to be the case then should we look to develop all negative films of say 400 at 320,250, 200 and how will we know which?

Secondly are the black and silver boxes on a slide cassette different to ensure that the camera "knows" it has a slide cassette in it and sets the ISO/EI in the opposite direction

Again how do black and silver boxes on a cassette do what appears to be an amazing thing?

Sorry it may be me but I still haven't grasped how this happens

pentaxuser

abruzzi · Mar 11, 2019

pentaxuser said:
Not wishing to act as the "wise-guy" but I am still unsure what the exposure tolerance in DX coding can actually do or does in reality.

Part of my question is exactly this, but the only camera I’ve found with second row contacts are this MZ-S, and nothing in the manual states how, or if, it is used. If you look at the Wikipedia page you can see what values can be encoded in the exposure tolerance line:

+/- 1/2 stop
+/- 1 stop
+2/-1 stop
+3/-1 stop

What the camera does is in the event of this information, I don’t know. Some auto exposure cameras (point and shoots mostly) won’t take a picture if it can’t make a correct exposure. The suggestion that it might simply extend the range of acceptable exposure at the upper or lower range of exposure makes sense. It’s a lot simpler an explanation than my initial thought about matrix metering and complicated “zone system lite” ideas.

DX Coding, Exposure tolerance

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