DX Code Compatibility with 4 Contacts (Ricoh One Take AF)

[nickandre]

Just a curiosity: I see my new-to-me "Ricoh One Take AF" has four DX contacts. It has no capability to enter in any exposure parameters save those contacts. I cannot find very much info on this camera online and am trying to figure out what its behavior is.

I think technically 4 DX contacts (with the ground and 3 additional contacts) should make it able to read film speeds from 25-3200 in even stop increments. I would assume that either 3200 and/or 25 are read as "default" since I assume a cartridge without DX coding would read as either of those. Apparently 25 is "no continuity" and 3200 is "all contacts bare."

Anyone familiar with what to expect? I put in a roll of Portra 800 (siblings want the "instant camera" look ) so I guess we can see how that works.

--Nick

 

[ic-racer]

Many cameras default to 100 iso

 

[nickandre]

Many cameras default to 100 iso

Yeah that was my assumption. I found a similar model which advertised the available exposure values without mention of default:

Film speed range: Automatic setting with DX coded film ISO(25, 50, 100,200, 400, 800 1600, 3200) with color negative film

https://www.butkus.org/chinon/ricoh/ricoh_mirai_105/ricoh_mirai_105.htm

Probably not a huge deal on the default. I believe the 160 Portra will look like 100 without the extra contacts to see third stops.

 

[wiltw]

The DX code is a bit more complex'

"Next to the film exit lip is an Interleaved 2 of 5 barcode and a printed number. The 6 digits represent the I3A assigned DX number (middle 4 digits), the number of exposures (last digit) and a proprietary manufacturer's code (first digit). The DX number identifies the manufacturer, film type, and by inference, the necessary developing process type. This is used by automatic photo-finishing machines to correctly process the exposed film."
​

Then there is a code which is read by the camera:

"The outside of film cartridges are marked with a DX Camera Auto Sensing (CAS) code readable by many cameras. Cameras can then automatically determine the film speed, number of exposures and exposure tolerance.

"The DX Camera Auto Sensing code takes the form of a grid of contact points on the side of the metal cartridge surface that are either conductive or non-conductive. Electrical contacts in the camera read the bit pattern. 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."

"On 35mm film cartridges there are two rows of six rectangular areas. The two left-most areas (with the spool post on the left) are both common (ground) and are thus always bare metal. The remaining five bits in the top row represent 32 possible film speeds. But only the 24 speeds representing the 1/3 stops from ISO 25/15° to 5000/38° are used. The codes are not in strict binary order.

In the second row, the first three bits represent eight possible film lengths, although in practice only 12, 20, 24 and 36 exposures are encoded. The remaining two bits of the second row give four ranges of exposure tolerance, or latitude.

Most cameras read the film speed only (first row)."
​

This article is the source of the above, and explains more, with illustrations of the codes.

https://en.wikipedia.org/wiki/DX_encoding#:~:text=DX (Digital indeX) encoding is,photographic film and film cartridges.​

 

[ic-racer]

I made DX labels pretty easy with some aluminum tape and a label maker: