Pinouts for zoom stubs

Zoom stubs (or zoom demand unit)

One of the first accessories I bought for my camera, some quarter of a century ago, was a zoom stub.  Standing with my arms wrapped around both sides of the camera so I could simultaneously zoom and pull-focus was awkward, and it made it very hard to to pan and tilt at the same time.  My fingers weren't quite long enough to comfortably use my left hand over the entire lens, reaching over it to the zoom rocker, using other fingers for focus, and thumb for iris, freeing my right hand for the panning arm.  And having to work with the tripod at awkward heights to get the required shot just makes it even worse.

ENG style cameramen do not have a focus-puller assisting them like a cine-cameraman does, nor a grip, we have to do everything ourselves.  So I bought the Fuji SRD-91B (pictured nearby) soon after buying the camera, for the staggering price of around $500 in the early 1990s.  This lets you use your left hand for iris and focus, and your right hand for zoom, pan, and tilt.  And then within a very short time the plug broke.  Cutting the moulded plug apart, I found the wiring was badly soldered to the pins, and one of them barely soldered at all.  And, later on, I had to deal with using lenses from different manufacturers.

These are the pinouts I have collected from various lenses and controllers (zoom rate demand units, or zoom stubs), for where the hand control plugs into the lens.  Commonly found on professional ENG/EFP camera lenses on broadcast and industrial video equipment.  Large studio cameras usually use different connectors.  And they're both entirely different from people using SLR styles of cameras for video recording.

They use a sprung-loaded rocker for controlling the zoom servo motor, the further you push the rocker the faster the motor goes (unlike many consumer lens zoom controls which have just one or two speeds, and is always inappropriate for the type of shot you want).  Usually there's a REV switch to reverse which direction is wide or tele, sometimes hidden inside the zoom stub, to suit your preferences and the lens (different lenses rotate in opposite directions for wide or tele).  Sometimes there's a speed knob to set the maximum speed the zoom motor can run at (if not a user control on the outside, an internal preset).  There may be a zero balance trim (usually inside) to stop lens-creep when you let go (it adjusts the null point voltage so the zoom doesn't move until the rocker is pushed in either direction).  There's usually one REC button for record start/stop, and there can be one or more RET buttons for return video viewing (studio cameras might have more than one video feed available), which is often used for replaying the end of the last shot on camcorders.

Usually there's very little electronics inside a zoom stub, most of the brains is in the motor unit mounted on the side of the lens.  The zoom stub is mostly just pots, springs, and switches, little more than the basic schematics I've drawn below.  The motor unit will house the motors, the controlling circuitry, and often has position sensors that monitor how far the iris ring has rotated, sometimes a sensor for the zoom ring, and sometimes one for the focus ring, too.  They're just a very low friction pot that provides a sense voltage back to the camera, and the camera may show lens details in the viewfinder (useful if you can't see the lens markings from behind the camera, although it can clutter the viewfinder with too much information superimposed over the picture).  The large box lenses on studio cameras can have more elaborate features, like range-extenders (magnifiers), and remote control of lens functions.

I have encountered cheap amateur zoom stubs that should also work on professional cameras, although one (Libec ZC9Pro) had various pins joined together that should not have been.  While it may have worked with the lenses they tested it with, it didn't work properly with the lens I tried.  Once I removed the erroneous connections, to be the same as the Fuji & Canon diagrams that I've drawn below, and modified it to have a zero-trim adjustment, it's worked with every lens I've tried it on.

I didn't think very highly of that cheap Libec stub (cheap as in less expensive than a proper zoom stub, but still expensive to buy—very much so for how it's actually built).  While there's logic to it just being a small box you mount above your panning arm grip (and you continue to hold the panning arm), as opposed to professional zoom stubs where it has a handle that you grip while panning (and you don't use the tripod's handgrip anymore), it mounts the zoom-rocker too far out from the panning arm, and you have to uncomfortably bend your thumb too far backwards to use it.  It could be designed better to sit in some other position on the arm, or much closer to it.

Professional zoom stubs have their own design issues, as well.  They're usually predominantly right-hand operation designed.  Not just in where the switches are, but also where the mounting bracket attaches to the side of the zoom stub.  The plastic or rubber coating on their own handgrip tends to die after a few years, this one's been wrapped with gaffer tape so I didn't have to hang onto bare metal while filming outside in the cold.  And you have to attach them very tightly to stop them slipping around the panning arm, so tightly that I've come across many badly mangled ones by careless people being far too aggressive in fastening them in place.  A thin strip of rubber stuck around the panning arm can help.

Most of these simple controllers can be hot-plugged (connected or disconnected while the gear is running).  There won't be any damage caused by doing so, though you might get a momentary glitch of lens behaviour while doing so.  More complex ones might require the equipment to be off, such as large studio camera controllers using serial data communication.  The thing to watch out for is correctly orienting the plug before trying to insert it in the socket.  They only fit one way, and grinding the plug around until it mates breaks things (damages the locating pins and slots, and starts to unscrew the backshells).  Connectors with loose backshells need to be fastened up properly, else you're likely to break the tiny wiring inside the plug.

A few notes (below) talk about common + and common − references, although there aren't any negative voltages actually there.  The + voltage is higher than another, and the so-called − is less than some mid-way reference voltage.  So negative, relatively speaking, but not actually negative compared against the zero volts ground.  Most of the lens circuitry is running from a +12 volt supply and zero volt ground, with all control voltages and signals somewhere between them.

Sockets on lenses

It's not unusual for lenses to have several control sockets on it.  There may be one for a zoom controller, and another for a focus controller.  There may be one for a zoom controller, another for power to a focus motor, and the focus controller plugs into the focus motor attachment.  Some could have two alternative types of sockets both for zoom controllers.  Some could have two sockets where you could connect either controller to either socket (the zoom and focus functions being on different pins, and the different controllers only use the pins meant for itself.  It's also possible to have just a single socket that both zoom and focus controllers connect to (often the focus controller plugs into the zoom controller, and the zoom controller goes to the lens).  And there could be lens and controller combinations that are completely proprietary and not compatible with anything else.  It's next to impossible to provide a simple set of connection and wiring instructions.

8 pin connector with a threaded locking ring

Depending on the manufacturer, some number the pins 1 to 8, others use the letters A to G.  Tajimi is one brand that I know of that makes these connectors.

These controllers tend to be basic, with just a sping-loaded rocker potentiometer for the zoom, sometimes a max-speed pot, and usually have REC (record) and RET (return video) buttons.  Cheap stubs may not have the RET button, or may have a switch for a button to be either a REC or RET button.  I didn't get why they did that, they still have two controls on the unit, they may as well have just put two buttons rather than make you use a mode-swap switch.  I'm tempted to rewire one of mine so that the button is always the record switch, and the mode switch is a latching RET switch.

The RET switch is usually used to either see return video from a vision mixer coming back to the camera in the viewfinder, or to trigger a replay of the end of the last recording made.  In a studio/EFP situation, it can be handy to have a viewfinder stay showing the line-view when you're filming effects shots.

Similar controllers may use a pull-to-release locking collar, with a different number of pins, and a pinout that I don't have to hand, at the moment, but I've included unverified notes further down.

Large studio cameras have more elaborate controllers with a much larger plug, as well as the above-mentioned controls, there may be extra return video buttons, shot box buttons (zoom position presets), lens magnifier controls (multiple range extenders), intercom controls, etc.  Sometimes there's several connectors for each type of control on camera lens, sometimes there's one big connector on the lens, and the various control boxes on the tripod arms plug into the first control box.

Fuji lens 8-pin

According to a Fujinon Th16×5.5BRMU lens manual, pins E and G are joined to its signal and chassis ground.  A has 7.5 volts, D has 5 volts, and C has 2.5 volts on them, they're reference voltages for the control pots, not power supplies.

Some stubs have a switch to swap A and C over, allowing you to change the direction that the spring-loaded zoom-rocker works regarding zoom in and out.  Normally I push in with my right thumb to zoom in, this direction can be reversed, or you could think of it as a left-hand/right-hand mode switch (ENG cameras usually have focus on the left and zoom on the right, studio cameras usually have the controls the other way around—zoom shots are rare, and focus is considered a critical high-speed adjustment).

Zoom stubs with a speed knob will insert a pot between pin B and the wiper of the zoom-rocker pot, to let you slow it down even further.  Ordinarily you'd run the zoom motor as fast as possible, to aid in rapid focussing between shots (fast zoom in, focus, quickly zoom out to the required framing).  But if you had to do a slow precise zoom shot, you could turn the speed down.

Inside the zoom stub there will probably be a centering preset, which is a trimpot in parallel with the zoom-rocker pot, allowing you to null-out the zoom-rocker so the lens zoom doesn't creep when the rocker is at rest in the central position.  I've had to add one to a cheap Libec ZC-9Pro zoom stub to fix that problem.

On the same centre-null issue, I've seen a JVC KY-2000 camera service manual (which includes two different lens and controller schematics) where the reference voltage on the D pin goes to a centre-tap on the zoom rocker pots (on the lens, and the zoom stub), and to a common rail in the lens electronics.  This helps to null out the zoom-rocker when you let go of it, without needing very fiddly fine-adjustment trimpots.  And my Fujinon SRD-91B zoom stub has a very low resistance between pins B and D when the zoom-rocker is at rest in the centre position.

Older zoom stubs may have a latching switch for the record button, but most controllers use momentary push buttons.  My SRD-91B did have a latching switch and I had to swap it over.

I saw a cheap zoom stub that had the REC and RET switches wired between F & G, and E & H.  While this may work with some lenses, because E & G were connected to ground (and, thereby, each other), with F being the record and H being the return, it is contrary to a Fujinon manual, and may not work with other lenses (if a manual specifies that the switch goes between E & F, then either E or F could be a signal input, and either F or E could be the ground; likewise with G & H).

Canon lens 8-pin

Almost the same as the Fuji one, but with pins A and B swapped.  In zoom stubs with a Fuji/Canon switch, the switch simply swaps the wiring over between pins A and B.  And you can modify the wiring inside the zoom stubs in the same way, if you have a non-switchable stub of the opposing brand for your lens.

I don't know if Canon and Fuji deliberately chose incompatible wiring from each other just to ensure buying a lens from them meant you also had to buy their controller.  We're probably lucky that they didn't make every lens different from each other.

Like the Fuji, pin D is probably a zoom-pot centre-tap, too.  Different lenses and controllers seem to use, or not use, this feature.

Tamron lens 8-pin

The Tamron controller wiring is completely different and incompatible.  It also has some electronics in the zoom stub for the zoom control, rather than simple passive components.  I think the ZOOM REF is to do with the centre nulling of the zoom-rocker, but the manual had no wiring details.  I'm not sure if a Fuji or Canon zoom stub could be rewired to suit a Tamron lens, or vice versa.

This info taken from the service manual of a JVC KY-2000 camera.

Zoom centering

Lens creep is an issue where the lens motors to zoom by itself, even when not being commanded to.  One cause is using an unsuitable controller for the lens (wrong brand, or focus and zoom controllers plugged into the wrong sockets), another is the controller not properly zeroing-out in the centre of its mechanical range, and another is the controller not mechanically returning to the centre position when released.

Common to many zoom stubs are one or more ways of making the zoom stub stop driving the zoom motor when the zoom-rocker is released and it's returned to its spring-loaded centre position.  Some employ several of the methods.

A trimpot across the zoom-pot, in parallel, to trim out any inaccuracies in the zoom-pots centre position.  I've just shown a simplified schematic, it's likely to have fixed resistors between it and the zoom-pot, so that the trimmer only has a limited influence on the zoom-pot.  This trimpot can be in the zoom stub, or in the lens barrel, or both.  One in the lens barrel to balance the system when no zoom stub is attached (to be adjusted, first, without a zoom stub attached), and one in the zoom stub so that attaching it doesn't change the lens behaviour (to be adjusted after the internal centering trimpot has been set).

It's not unusual to have to re-adjust a zoom centre trimming if connected to a different lens, or vice versa.  The next technique may make the zoom stub more universally compatible with various lens, avoiding a need to trim it out, or having to trim it so precisely:

A centre-tap to the zoom-pot connected to a reference voltage mid-way between the reference voltages sent to each end of the zoom-pot.  This helps to electrically hold the centre of the pot at a half-way point, even if the pot resistance is not exactly equally divided.

It's also possible that the centre tap could just go to a sense input, so that when the wiper output has the same voltage as the centre-tap, the drive circuit is nulled.

Some zoom-pots have a dead spot in the middle, the zoom in/out resistance tracks go either side of it, with a enlarged spot in between them with zero ohms across it (for a wider centre-null area).  Or it could have a non-conductive patch disconnecting the zoom-rocker's wiper.  This can help stop the motor from being driven if the zoom-rocker doesn't mechanically centre itself very precisely.

Some lenses can have a null control that renders an adjustable range around the centre position to not drive the zoom motor.  It means the zoom-rocker has to be pushed further before anything happens.  That can help with worn out and sloppy rockers, and imprecisely adjusted centre-trimmers, but can also be overdone so that you have to push too far before anything happens, and then the zoom suddenly starts moving too fast.

12 pin connector with pull-release locking-ring

To begin with, this section is the sockets on the lenses to plug the zoom controllers into.  Further down are notes about the lens connector on the camera body (which uses a similar, or perhaps identical, connector).  Hirose is one manufacturer, you may see their connectors with a HRS brand mark on them.

There are zoom stubs with the same features (record, return, zoom) that come in 8-pin or 12-pin versions, and are simply wired to a different plug.  Some of the 12-pin connectors have spare un-used pins, others have extra features on them.

You'll notice that they're not consistent with each other, so you'd need to take measurements, or track down schematics for your equipment.  This info could be wrong, or only pertinent to certain equipment.

Copying someone's info, it appears to be for a Canon controller but I don't know what lens it's for:

And another person's info from a Fujinon manual:

Some of their listings don't seem right.  It looks like they've crossed D and B over, where I've typed [?].  The [zoom-pot] are my additions, as to where I expect them to go.  Where they've used A as a zoom control suggests a Canon zoom stub, yet they were talking about Fuji.  And the zoom control (stub to the lens) has the opposite voltages from the zoom position (lens feedback indicating the current zoom position?), which I suspect has one of them the wrong way around.

Someone else's info from Fuji:  (I don't know if this is the same small 12 pin connector, or the larger one from some studio box lenses.)

1. Focus mode select
2. Zoom mode select
3. 0 volts (ground)
4. Iris local/camera select
5. +12 volts out
6. Signal common reference +5 volts
7. Focus control signal
8. Zoom control signal
9. Iris mode select
10. +V out (7.5 volts)
11. -V out (2.5 volts)

Someone else discussing connectors on the Fuji BMD lenses:  (I'm guessing Fuji lenses on Black Magic Design cameras.)

1. Focus mode: 0 volts servo off / +12 volts servo on
2. Zoom mode: 0 volts servo off / +12 volts servo on
3. Ground
4. Iris mode: 0 volts local iris / floating-open auto iris
5. Iris control: pot wiper, pot between +2.25 and +6.67 voltage references
6. +12 volts supply
7. +4.5 volt reference (probably zoom centre)
8. Focus control: pot wiper, pot between +2.25 and +6.67 voltage references
9. Zoom control: pot wiper, pot between +2.25 and +6.67 voltage references
10. Input for something they didn't figure out [probably the iris]
11. +6.67 voltage reference
12. +2.25 voltage reference

Connectors on the camera body

These are for where a camera controls the lens, and some things on the lens give signals back to the camera.  You can see that there's some commonalities, but also differences that either make some combinations of lenses and cameras incompatible (because of different things on some pins), or some combinations will be more rudimentary (because of omission of some things).  The incompatible devices may be destructively incompatible.  Thus far, these all seem to be using the same Hirose 12-pin pull-to-release locking-ring connector.

Cameras often only had a small range of compatible lenses available for them.  The lenses would usually be various Fuji or Canon lenses with customised electronics or lens-mount fittings.

Normally, I expect “position” to mean the position-sensor potentiometer and switches on the lens, indicating to the camera what some status of the lens is.

Focus demand units

There are two basic types of focus demand units:  One is a relative control that spins around with no end-stops—as you spin the knob, the motor is driven in the direction that you turn.  The other is an absolute control, which has a fixed rotating range from near to infinity, and the lens will track to the position you rotate the knob to.

Many ENG/EFP lenses won't have a motorised focus control, only a mechanical linkage so a hand-driven controller can be fitted.

None of the focus controls are likely to have any distance markings on it.  Unlike a remote used by a focus-puller on a cine camera, focus control on a video camera is normally used without looking at the controller.  Your eyes will be on the viewfinder (which may have lens status info), occasionally looking at the lens, or other camera controls.

While most lenses have internal motors for zoom and iris, many don't have a focus motor and you fit an external one to the lens.  These lenses tend to just have a simple two- or three-pin power connector for the motor, and the controller plugs into the motor box.