DX coding range.

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Here is an image of the DX reading pins on my Boots 350Af camera. I guess it's typical for its day.

It looks to me as if the top pin of the set is missing (as well as several pins at the bottom) when compared to a full set.
I know that this will reduce the range that the pins (camera) can detect. I've studied the pin layout for a while too long,
coming to the conclusion that this camera will not see the difference between a 100 film and a 200 film, the next step from 100 being 400. Is this correct?


DXpins.jpg
 
Nod said:
Wiki's page on Dx codes might help.

en.wikipedia.org

DX encoding - Wikipedia

en.wikipedia.org en.wikipedia.org
Click to expand...
Thanks, it's exactly that chart that made my head spin. My reading of it doesn't align with 100 or 200 speed cassettes unless I renumber column 6 as 5, 5 as 4 etc. It looks as if they have used one numbering system for the photo of a cassette (1 to 6) and a different system for the chart (G + 1 to 5).
 
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Ah! the video defines the DX markings as G + 1 to 5 which then matches the table (the same table as seen on Wiki). This makes more sense.
 
The Wiki entry shows the contacts on the cassette as numbered 1 to 6, with 1 being ground. It then discusses contacts S1 to S5, these being what was previously listed as contacts 2 to 6, and thereafter refers to them as 1 to 5, meaning S1 to S5 and not 1 to 5 as in the images of the cassette... a mistake easily made by those (like me) not paying attention.
 
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Your answer is right in the above Wikipedia article. :) The common film speeds of 100, 200, 400 and 800 can all be determined just by using the first 3 pins in the DX spec, namely ground, S1 and S2. The remaining pins in the first row (S3-S5) are only needed for speeds outside that range. This only becomes a problem if another film speed uses any of S3-S5. For instance, as ISO 50 uses the same S1 and S2 pattern as 800, but is differentiated by the S3 contact, so that means that any camera with only the pins for ground, S1 and S2 will automatically read it as ISO 800 whether the rest of the pattern differentiates it as ISO 50 or 800 (or ISO 64, 80, 1000 and 1250). Somewhat cleverly though, when you have S1, S2 and S3, but lack S4 or S5, the ISO ranges are all within a 1/3-2/3rd of a stop of the actual speed and therefore very little difference is likely to result because of latitude. ISO 100,125 and 160 all use the same S1-S3 pattern and are only differentiated by the S4 and S5.

Very few cameras actually even sense the second row of encoded information for film length and latitude, even very high-end ones would only look at the film length at most. Looking at pictures of various pro level cameras, only the Minolta Dynax 9 seems to have the full set of pins for the second row.

After I wrote the above and did the below picture, I realised that it doesn't actually apply to your camera, which looks unusual as the positioning of the pins suggests to me that it reads S3, S4 and S5 or S2, S3 and S4? (if you could post a picture of a film roll lined up with the camera it would be easier to tell). From either of those combinations you can get a good range of speeds. In the case of having S2, S3 and S4, that means that 100 and 200 would read the same, as would 400 and 800 and various other combinations such as 500 and 1000, 160 and 320 etc. Note that these are all doubles and therefore there will be at the most only a 1 stop under/exposure. I did find a picture of the specs in the manual at
https://flic.kr/p/SSC9eW
View: https://www.flickr.com/photos/nefotografas/33390714952
and noted that it only lists the ISO range as between 100 and 400 and specifically recommends against slide film. To me that implies that it probably has a simple set of rules programmed where combinations it reads will always be interpreted as one of a set of speeds, like being "high", "medium" or "low" or something. Negative film has excellent latitude anyway, so most people would probably not notice any difference in the overall end picture. I don't quite understand though why they didn't just go with a much simpler scheme using only S1, S2 and S3 or even just S1 and S2!

This is a similar idea to how film speed was encoded on 110 film cartridges, which used the presence or not of a tab on the cartridge to set the camera to meter at either "low" or "high", with the idea being that the exposure latitude would be enough to compensate for other speeds in between or outside. Low and high were unfortunately not exactly defined and each camera manufacturer made their own decision - my Pentax Auto 110 uses 80 and 400 for instance. As 99% of 110 cameras didn't take advantage of reading this tab though, it did mean that ISO 200 film was at a decided disadvantage if you were using a higher end camera like a Pentax Auto 110 SLR. Fuji Susperia 200 was the last 110 film made until Lomography revived it, but unfortunately Fuji chose to encode it as high speed rather than low, which led to underexposure and really didn't help with the grain from such a small negative in the first place. You could however alter the cartridge to read as low by simply filing the tab off!

DX.png
 
Thanks for your help. As far as I can see, the end "contact", S5 has no pin in that position. Seems odd to have pin S4 when it never changes across the range of film speed, but it will act as a ground connection, so the film range will only see two speeds, I guess. Camera is now loaded with 400 film. I will check again and photograph it at the next chance.
 
Now that I have a better understanding of DX coding, I looked over a few of my P&S cams.
One has the bottom four pins, S1 to S4, giving it the ability to see a good range of film speeds.
Another has only one pin, but closer inspection showed that it has a double contact in the one pin position. I guess that coincides with the spec of either 400 or 100 speed, if no 400 DX cassette, then that defaults to 100 also.
 
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