A Mystery Resolved (at least for me)

[Michael Hiles]

Advertisement (gone after registration)

Our esteemed colleague, Michael Geschlecht, has shared with me an interesting and useful item – a “decoder” that unwraps the meaning of the code found on film cassettes – the two rows of black and white squares that tell automatic cameras something about the film they are managing. The decoder information is thanks to both Michael (who has kept it on file and has shared it), and Modern Photography magazine, of late lamented fame.

 

So… thanks to Michael, and to Modern Photography for providing us with something a little rare and useful.

Film_Decoder.pdf

[mikemgb]

Very handy, thank you both!

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[Michael Geschlecht]

Hello Michael,

 

Thanx for putting this on the screen in the Forum. I am pretty much of a computer illiterate in terms of doing these types of things.

 

As to the P.M. I just sent you: I figured things out by myself & now can read the Red reference. Altho I am not exactly sure what I did or how I did it.

 

A note to anyone using this "Decoder":

When reading the little boxes: Always hold the film cartridge with the little "nubbin" to your left. Even if you are left handed.

 

Also: Squares numbers 1 & 7 are always white & are NEVER read as values when deciding what the film speed written on the box is. Or when reading how many exposures are on a roll of film.

 

Numbers 1 & 7 are the top & bottom common contacts which are needed so that 2 thru 6 as well as 8 thru 10 and 11 & 12 can be read correctly.

 

All of this data provided in this decoder assumes that the person will take the film for that manufacturer's recommended processing for: Exposing that film at the ISO written on the box.

 

An explanation of the term "corrections":

 

The "corrections" made by me were to the CHARTS that: Using numbers 2 thru 6, tells the CAMERA what ISO film speed is written on the box. Using numbers 8 thru 10, tells the camera the number of exposures on a roll & Using numbers 11 and 12 tells the camera the latitude of the film assuming normal processing as per manufacturers instructions on the box. These corrected charts also tell the same thing to anyone who reads the little squares on the cartridge.

 

When this magazine came in the mail (Snail Mail) in 1983: There was an article explaining what these little squares meant, and more. Along with the diagrams. The captions in the diagrams are as they were written. The drawing of the ISO chart had some SMALL errors in it. I ONLY made changes for the errors in the ISO chart: So that the chart now matches with & agrees with both the text in the article & the text in the captions in the diagrams.

 

Best Regards,

 

Michael

Edited April 5, 2017 by Michael Geschlecht

[Michael Geschlecht]

Hello Everybody,

 

Here is an example with the "nubbin" to the left:

 

W - W - B - B - B - W

 

W - B - B - W -B - B

 

This is Kodachrome 64

 

36 Exposure Roll

 

With 1/2 of a Stop +/- of exposure latitude.

 

Best Regards,

 

Michael

[Michael Hiles]

Thanks Michael - I am glad the red link worked for you. I was surprised when I posted the OP - I was expecting the file to appear as a image much like a picture.

 

If anyone has a technical problem, I can create a jpeg and post it. Just shout.

 

Moreover, Michael many thanks for added explanation. Very useful.

 

Best,

 

Michael

[Michael Geschlecht]

Hello Everybody,

 

An interesting observation:

On occasion someone will come to the Forum & say that their M7 reads their film cartridge as containing a film of ISO of 5000 film. Even though they had put a film with a different ISO in the camera.

 

Sometimes it turns out that they had loaded the film themselves into a reloadable film cartridge that has a shiny metal surface all over.

 

If the surface is all shiny then the "decoder" IN THE CAMERA reads that cartridge as being a 72 exposure roll of ISO 5000 film that can be used at its marked ISO or up to & including 3 stops of overexposure or up to 1 stop of underexposure & then processed normally as per the instructions on the box & the photographer will still get properly exposed negatives or transparencies.

 

Best Regards,

 

Michael

Edited April 5, 2017 by Michael Geschlecht

[Michael Geschlecht]

Advertisement (gone after registration)

Hello Michael,

 

If that is possible & it is not too much work: Having the diagrams on the screen here might be helpful. Especially for people like me who are somewhat computer challenged.

 

Thanx again.

 

Best Regards,

 

Michael

[Michael Hiles]

No problem - here we go as a JPEG file.

Welcome, dear visitor! As registered member you'd see an image here…

Simply register for free here – We are always happy to welcome new members!

[pico]

The diagram does not directly relate to the Leica M7 which reads only one row, of six rather than having 12 sensors as shown in the  document.

 

The M7 does not read the extended code which contains the latitude of the film, and less important number of frames (length) of the film.

 

 

Edited April 5, 2017 by pico

[Michael Geschlecht]

Hello Pico,

 

Thank you.

 

I guess that means that if someone used a cartridge that was shiny where the film speed boxes are: Then the camera would just read the cartridge as ISO 5000.

 

By the way, do you know if both versions of the reader just read the set of boxes that tell the ISO speed?

 

Best Regards,

 

Michael

[pico]

I guess that means that if someone used a cartridge that was shiny where the film speed boxes are: Then the camera would just read the cartridge as ISO 5000.

 

By the way, do you know if both versions of the reader just read the set of boxes that tell the ISO speed?

 

Don't try to make sense of the blocks in terms of binary representation of ISO. They just correspond to a table look-up.

 

If set to DX and the reader does not recognize the cartridge coding, then '100' flashes for a couple seconds and ISO 100 is used. This happens if none of the positions can be read (non conductive).  If all positions are conductive, it's ISO 5000.

 

The optical reader has the same number of sensors/readers and behaves the same as mechanical sensor/reader.

 

EDIT: A fellow who ran a processing machine told me that the bar code (stripes) are read by the processing machine to find film type and other data. The printing machine read the bar code along the edge of the film for more information. He could read them. I never even tried.

Edited April 5, 2017 by pico

[Bobitybob]

If you are looking to modify the coding or make your own labels  take a look here http://www.instructables.com/id/DIY-film-DX-code-labels/

[Michael Hiles]

Thanks Bob. Interesting and potentially useful.

[Michael Geschlecht]

Don't try to make sense of the blocks in terms of binary representation of ISO. They just correspond to a table look-up.

 

If set to DX and the reader does not recognize the cartridge coding, then '100' flashes for a couple seconds and ISO 100 is used. This happens if none of the positions can be read (non conductive).  If all positions are conductive, it's ISO 5000.

 

The optical reader has the same number of sensors/readers and behaves the same as mechanical sensor/reader.

 

EDIT: A fellow who ran a processing machine told me that the bar code (stripes) are read by the processing machine to find film type and other data. The printing machine read the bar code along the edge of the film for more information. He could read them. I never even tried.

 

Hello Pico,

 

I never wrote anything about "making any sense" about the boxes as shown. Beyond simply reading them.

 

I am sorry that you misunderstood what I wrote.

 

To clarify what I wrote as per an all "shiny/white" cartridge surface coming in contact with the ISO reader:

 

I was simply saying that the shiny/white surface equated to a continuous series of shiny/white boxes. That's all.

 

Best Regards,

 

Michael

Edited April 6, 2017 by Michael Geschlecht

[Michael Geschlecht]

Hello Everybody,

 

At the time these little boxes on film cartridges were introduced in the early 1980's: It was said that the reason for the section of boxes, 8, 9, & 10, with the number of exposures in each individual cartridge: Was to tell the camera when to turn off film winding motors after the requisite number of exposures had been made.

 

Boxes 11 & 12 are interesting.

 

11 & 12 tell the camera what the latitude of the film in that specific CARTRIDGE is: When the film is processed at that manufacturers recommended processing recommendation for negatives or transparencies exposed at the ISO on the BOX that contains that specific cartridge.

 

This information from 11 & 12 sometimes gives the user of the film, whether negative or transparency, the ability to make certain adjustments to their exposure determination process that may, at times, be beneficial.

 

While, at the same time, maintaining standardized development of the negatives or transparencies. As per the manufacturers recommendation on the box for the film speed on the box.

 

An example of where there is no ability to adjust for circumstances is Kodachrome 64. Which, as we all know is no longer available. Kodachrome 64 has an 11 - 12 of B - B. This means that the exposure should be within +/- 1/2 stop for best results with normal processing.

 

An example where there is more ability to adjust what is captured by the negative while producing an appropriate exposure & still maintaining the manufacturers recommended standardized processing would be another old film: Kodak Gold 100. 

 

Kodak Gold 100 (Which is W - W in boxes 11 & 12 respectively.) will produce perfectly nice negatives when exposed at an ISO of 100. This will allow 1 stop of underexposure and 3 stops of over exposure. Given manufacturers recommended standard processing.

 

BUT:

If the ISO were lowered to an ISO of 50: Then negatives exposed at ISO 50 with manufacturers recommended processing for the ISO 100 written on the box: Would produce perfectly nice negatives with a latitude (Think room for error in exposure determination) of +/- 2 stops.

 

That is a reasonably nice safety margin compared to the 1 stop on the underexposure side when the film is exposed at ISO 100 and certainly workable with its 2 stops of overexposure tolerance at ISO 50 compared to the 3 stops of overexposure tolerance at ISO 100.

 

This would also allow for bringing more detail out of the shadows, while, at the same time, not jeopardizing the highlights.

 

Something to think about.

 

Best Regards,

 

Michael

Edited April 6, 2017 by Michael Geschlecht

[pico]

The first 'box' codes on the cartridge indicate ISO, and are part of the story. Only high-end early cameras, mostly amateur units, read the second line of box codes.

 

The bar code on the cartridge and the bar code on the film are other parts, and they serve different purposes, and of course neither are read by the camera, but by the processing machine and printing machine, respectively.

 

I've never used a camera that read anything but the ISO, and in those cases, such as with my M7s I over-ride when necessary, as most do.

.

Edited April 6, 2017 by pico