Continuing on from my work last week replacing the belts in the ARRI 35 BL 4S, this week I set out to repair the broken video tap. The damage was likely caused by someone mistakenly picking up the ARRI camera by the video tap. I have seen this on a number of other cameras from various manufacturers, where the video tap itself is an accessory that sticks off the camera body.
What I have seen happen is that the weight of the camera body will either bend or shear off the video tap. In the case of this ARRI 35 BL 4S, it literally bent the video tap relay optics housing and sheared off the rear section of the lens that relays the image from the movie camera to the video camera.
To get everything back in working order, it was necessary to redesign and machine parts that would repair and support the existing relay optic, attach the optics to the video camera, and allow the optics to be coupled with the iris control that is part of the factory video tap prism housing.
On video taps that I have designed and built, I have usually made provisions to be able to adjust the prism or mirror that sends the image to the video camera as well as the relay lens and video camera itself. These provisions allow me to adjust focus and image position for perfect centering on the monitor. The video tap on this particular ARRI camera only provides adjustments on a prism that centers the relayed image in the up-down and left-right axes. So the challenge with this repair was to machine parts that held the video camera, the relay optic, and the iris control so that the video camera is centered and aligned as closely to what the prism sees as possible.
This was just many hours of trial and error during the machining of the replacement parts. Once I had a good, sharp, centered video image, I needed to make some sort of housing to protect and cover the repaired video optics. I went through a number of iterations of possible clam shell housings, but as they say, simpler is always better, so I made a sleeve that would slide over everything. Hopefully this will never need to be repaired again, but if it does, the sleeve will make access to all the new parts easy. The BL 4S is one of my favorite cameras. I have shot two feature films with one. I think its size, weight, and accessories make the ARRI BL system a great choice for any 35mm film work.
