DX Contacts

[David Hughes]

Hi,

There's twelve contacts needed to read all the DX markings/code on the cassette but most cameras have just 4 and one or two have 5. So I've been wondering and looking to find one with all 12 contacts. The nearest so far is a Canon with 6 contacts and a Pentax with 7.

An oddity is that several cameras have the four contacts with small indents in the moulding showing where the other eight or two would be.

Has anyone any thoughts on this? Apart from the obvious that 4 save money and makes using Ilford FP4 Plus (at 125 ASA or 22°) a minor problem but, then, what's a quarter EV between friends?

Regards, David

 

[Roger Hicks]

Dear David,

Possibly (I don't know) there are more ways than one to read DX, so that one set of contacts say how the others are to be interpreted?

And, as you say, if you care enough about a quarter-stop, you'll probably not rely blindly on (a) the meter and (b) the ISO speed.

Cheers,

R.

 

[Nomad Z]

All you want to know is here...

http://en.wikipedia.org/wiki/DX_encoding

Not all of the contacts are used for film speed, and two of them are ground returns. Film speed is a 5-bit code, giving 32 possible values, of which, apparently, only 24 are used (1/3 stop increments). The other 5 contacts are for number of frames and exposure tolerance.

 

[David Hughes]

Thanks for the replies folks.

I also wondered why two earths were needed or grounds as some call them. Spending years as a semi engineer (desk bound) makes me think things like that.

I've a DX Code chart somewhere but it merely adds to the mystery as I can't see why so much of it is ignored, or else I've not looked at enough cameras yet.

Regards, David

 

[btgc]

As a rule, more expensive cameras have more featured DX reader while cheapest can't even recognize intermediate ISO200, setting to ISO100 or 400 only.

 

[ronnies]

My F4 has 12 and my F65 has 6 contacts. The 12 contacts on the F4 are in pairs and each contact pair are very close together. Certainly not as far apart as the middle of each column of contacts on the DX panel on the cassette.

I'll check my P30t and Mju-II when I can get to them.

Ronnie

 

[David Hughes]

Thanks Ronnie; at last I've tied up another loose end.

A great pity that they came up with a 12 point system and then decided to mutate it into a simple 4 point version. But then, thinking of P&S's, I doubt very much if it matters.

Regards, David

 

[ronnies]

No problem David. I forgot that I'd looked at my other DX code reading cameras and found the following. The Pentax P30t has a similar 12 contact system to the F4, the Olympus OM40 has six contacts and the Olympus Mju-II has 4.

Ronnie

 

[David Hughes]

Nice to hear of one more with the full range, thanks.

Silly story based on above: having got into the habit of opening up camera backs and counting the contacts over the last few days or weeks, I'm in the flea market an had gone through several (all 4 and one with 3), I realised I was being watched and wondered about buying something. Carried on looking and found an almost mint Nikon in it's case. Asked the price and got it for a pound... Only a P&S but I've often found them to be excellent but limited by the maximum aperture.

Regards, David

 

[btgc]

Out of interest checked Ricoh FF-70 (90) - 9 pins plus 1 golden colored on bottom of left row, probably to check by pressure if canister is loaded.

Ricoh XR-X (XR-M) counts 9 pins, but interesting thing is each "pin" actually is a pair of two pins - looks like to directly read 0 or 1, depending on conductivity instead of figuring it out from neighbour pins.

 

[ronnies]

Out of interest checked Ricoh FF-70 (90) - 9 pins plus 1 golden colored on bottom of left row, probably to check by pressure if canister is loaded.

Ricoh XR-X (XR-M) counts 9 pins, but interesting thing is each "pin" actually is a pair of two pins - looks like to directly read 0 or 1, depending on conductivity instead of figuring it out from neighbour pins.

Isn't that what the ground pin should be doing. I'm not convinced the 'pairs' in the F4 and P30t actually read different panels and they're probably doing what you suggest, so why have a ground?

Ronnie

 

[ChrisN]

Pentax MZ5N has 7 pins.

 

[David Hughes]

Out of interest checked Ricoh FF-70 (90) - 9 pins plus 1 golden colored on bottom of left row, probably to check by pressure if canister is loaded.

Ricoh XR-X (XR-M) counts 9 pins, but interesting thing is each "pin" actually is a pair of two pins - looks like to directly read 0 or 1, depending on conductivity instead of figuring it out from neighbour pins.

I wondered about that, means we have pin number 1 missing perhaps or number 6?

Regards, David