Mechanics and electronics working together: Cable pulls in the Nikon F4 and other electromechanical SLRs

[Andreas Thaler]

Did you know that the computer-controlled Nikon F4 from 1988 still has a mechanical cable pull?

It is used to transmit the aperture manually set on the lens. Contacts (sliders) are moved via the cable pull along a ring-shaped resistance track on the rewind side of the mirror box.

Depending on their position, a certain voltage value is produced for each aperture, which is probably digitized and transmitted to the camera's computer.

However, other electromechanical SLRs also use cable pulls to transmit information, for example the Nikon F3, Nikon FA, Minolta XD, and Canon AE-1.



In the Nikon F3, a cable pull connects the aperture ring on the camera's bayonet mount to the disc-shaped functional resistor element (FRE) under the rewind crank. Depending on the position of the coupled aperture ring on the lens, the cable pull rotates contacts on the FRE, thereby transmitting values mechanically.



In the Nikon FA and Minolta XD, mechanical displays in the viewfinder are linked to the mode/shutter speed dial via a cable pull.



And in the Canon AE-1, the settings of the shutter speed dial on the wind side of the camera are transmitted to the functional resistor on the rewind side via a tungsten wire.

This and other fascinating collaborations between mechanics and electronics in electromechanical SLRs are described in detail in two documents. See the two articles by Master Larry Lyells on the Minolta XD and Canon AE-1.

Nikon's FRE is described in the Technical Manual for the Nikon F3 on page 25 (PDF).

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A word of caution

Please keep in mind that you’ll be using highly flammable solvents for service work, and their fumes are harmful to your health. Soldering also produces fumes that should not be inhaled. Dangerous high voltages can be present when handling electronics, especially in conjunction with electronic flash units and mains. Therefore, familiarize yourself with the safety regulations beforehand and ensure your safety. Depending on the activity, protective gear may be advisable.

All information provided without guarantee and use at your own risk.

Acknowledgments

Without the work of Master Larry Lyells, in particular, we wouldn’t have the detailed technical information we need today for service/repair of SLRs.

The SPT Journal and The Camera Craftsman, which he helped shape significantly as an author, and which contain all the necessary information and instructions are available for a fee through Learn Camera Repair.

We owe our access to them to Eugene Pate, the founder of Learn Camera Repair.

 

[Laurent]

I find this astonishing, especially since cameras like FTb use a rack and pinion, or the F1 "old" uses a rigid coupling between the two sides of the camera.

Maybe it was cheaper?

I have a Canon EF that has only one functional speed, and I suspect a pull-cord is the culprit. Did not open it yet...

 

[Andreas Thaler]

I find this astonishing, especially since cameras like FTb use a rack and pinion, or the F1 "old" uses a rigid coupling between the two sides of the camera.

Maybe it was cheaper?

I have a Canon EF that has only one functional speed, and I suspect a pull-cord is the culprit. Did not open it yet...

I believe that was the simplest way to mechanically connect two rotating elements that were separated from one another.

For example, turning the shutter speed dial causes a small disc-shaped mask on the prism of the Nikon FA to rotate via a cable mechanism, which is then reflected into the viewfinder.

Or, in the Nikon F3, the position of the aperture simulator ring around the lens mount is transmitted via a cable pull to the FRE (functional resistance element under the ASA ring). The FRE then transmits the respective position as a voltage value to the F3’s electronic signal processing system.

 

[Laurent]

I believe that was the simplest way to mechanically connect two rotating elements that were separated from one another.

For example, turning the shutter speed dial causes a small disc-shaped mask on the prism of the Nikon FA to rotate via a cable mechanism, which is then reflected into the viewfinder.

Or, in the Nikon F3, the position of the aperture simulator ring around the lens mount is transmitted via a cable pull to the FRE (functional resistance element under the ASA ring). The FRE then transmits the respective position as a voltage value to the F3’s electronic signal processing system.

I agree on the "simpler" argument , which is very close to my "cheaper". Making and adjusting a rack and pinion opinion is more demanding but more durable.

On the other hand, putting the right knot in the right place is not a trivial task (I just remembered there is such a thing in the old F1 also)

And when it breaks it's no longer easy to replace, I have a est of AE1 parts fort sale, all the enquiries I get are about the tungsten câble (which is unfortunatley missing.)

 

[lumoStoria]

Since I once broke the tungsten wire of my Canon AE-1 (it snapped when I opened the top cover not following the "official" way), I am very thankful to the Canon engineers for using a electronic/digital transmission for all camera settings. Also easier to analyze if the correct values are transmitted.