Focusbug Cine RT Rangefinder and WCU-4 Integration

May 28, 2019

Rangefinders like the Cinetape, Light Ranger, UDM-1, and the powerful newcomer – the Focusbug CineRT system – have been labeled by many a producer a luxury that surely any proficient camera assistant wouldn’t ever need. However, the conditions for pulling focus are becoming more demanding. Modern high-resolution sensors are getting larger and less forgiving, camera movement is getting less predictable (I’m looking at you, gimbal enthusiasts), and shooting schedules are getting tighter. Seriously, when is the last time you were given a proper marking rehearsal?

camera focus rangefinder

Rangefinders are an incredibly useful tool that help ACs do their jobs better. And the Focusbug CineRT is a really high-performing, fresh take on this piece of equipment. Not to mention the really interesting, unique features that show that Focusbug is willing to push the envelope. You can switch between (or view simultaneously) the readout from the on-camera horns and the Bug pocket transmitter. The measuring angle and sensitivity are fully adjustable. You can set up to 8 marks, and then this thing can literally sweetly whisper those marks into your ear via the headphone output. (Don’t worry 2nd ACs, it won’t push the cart around, change lenses, fill out camera reports, or keep the operator hydrated).

Not too long ago, configuring a camera with an ultrasonic rangefinder and a wireless follow focus required a sort of daunting amount of hardware and cabling added to the build (unless you are a #cleanbuilds wizard). Recent trends have onboard camera accessories becoming smaller, lighter, lower-profile, and increasingly wireless. Let’s take advantage of these feats of engineering and go through a lean, fully integrated camera build with a Sony Venice, Focusbug CineRT Ultrasonic Rangefinder, and an Arri WCU-4 with RF Motor.

Focusbug Cine RT Basic Setup

There are 4 main components to the complete Cine RT system:

  • Ultrasonic Base Unit (on-camera horns, the part that actually does the measuring)
  • Handset Control Unit (the touch-screen device that displays the distance and gives you all of the many controls the system offers)
  • High-Bright Distance Display (the small box that displays the distance only)
  • Bug Ultrasonic Transmitter (the tiny square that you can put in someone’s pocket).

Focusbug Cine RT base unit

First, Attach the base unit to the front of the camera. Use something that articulates, because there will be times you need to redirect the position. The base unit is the only part of the system that needs continuous power to operate, as everything else has an internal battery. The power input is a 2 pin Lemo receptacle, so use the included D-Tap to Lemo or Lemo to Lemo cable to power it up.

Once you have the basic position locked, ensure you have the base unit selected on the handset. Measure the distance between the back of the Base Unit and the camera sensor. This distance needs to be compensated for in order to get an accurate reading. You can then use the Handset Control unit to adjust the distance offset, by hitting the “camera sensor” symbol. Positive values are how far in front of the camera sensor the base unit is positioned, and negative values reflect the distance behind the sensor.

Focusbug Cine RT Rangefinder handset control unit

Theoretically, at this point you could be done with the setup. You have your rangefinder sending data to the handset, which you can mount on or near your focus pulling monitor. The High Bright Display typically gets mounted on the assistant’s side of camera, so you can see the distance with a quick glance. So long as the display is charged, you can just mount it to the camera however you choose. No cables required, unless you want. (seriously, it lasts so long it’s almost a non issue for a shoot as long as it’s charged.)

Now, we can begin to consider integrating this data into the WCU-4 ecosystem. The key device that joins the two protocols is the Arri LCUBE, or CUB-1. Somewhere on the camera body, mount the LCUBE using the Arri Locating ⅜”-16 bracket. Use the Focusbug serial to Arri 7 pin Serial cable to connect the serial ports of the base unit and LCUBE. This is more or less all you have to do with the Cine RT for the time being, let’s switch gears (HA) and focus (HA HA) on setting up the WCU-4. Sorry.


Setting up the WCU-4 Lens Control System using the CForce Mini RF Motor

For those used to using the WCU-4 with (most) Arri cameras, this process is not too different. The big difference is that, when using a camera that does not natively work with the WCU-4, you no longer need an external MDR to communicate between the handset and motor(s). The RF motor has a built-in MDR that controls itself as well as additional motors daisy-chained together with LBUS cables. This RULES because you can get a significantly lighter and cleaner build with fewer cables to mind, and still have all the creature comforts the Arri lens control system offers. Without further ado –

Arri RF motor

First, attach the RF motor to the rods with the rod bracket. Power the motor with a D-Tap, 2 Pin Lemo, or (if you want to utilize the run/stop feature of the WCU-4) 3-Pin Fischer to CAM cable. Once the motor is powered up, press the top button and cycle through the Focus, Iris, and Zoom axes to set the axis you’d like that motor to control. Use the bottom button to select a wireless channel to use (make sure it matches the channel on the WCU-4 handset). If you have more motors, simply connect them to one another via LBUS. At the end of your chain, connect the open LBUS on the motor to the open LBUS port on the LCUBE. Once the loop is complete, you should be able to see the distance readout from the Cine RT on the WCU-4 handset. Now just map the lens as you normally would, and your setup is complete. You’ll never blow a take again! Everyone will love you and you’ll quickly ascend the ranks until you are the industry’s premier and most-requested focus puller.

Okay Hollywood, back to reality. The truth is, to be a good focus puller, you still need to have a good sense of distance, great hand/eye coordination, a competent 2nd AC, and a healthy amount of experience under your belt, but a strong working knowledge of tools like this make an increasingly difficult focus pulling landscape more manageable and, debatably, a necessary tool for the job. There is so much more that these things can do, but I won’t re-write the manual. We are, however, always willing to demonstrate this and other products at the shop, so drop us a line if you are curious!