Helicon FB Tube – In-depth

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This article is intended for more in-depth understanding of the Helicon FB Tube operation.

So Helicon FB Tube is being mounted between the camera and the lens. Just as the lens, the tube has contacts serving for the camera to pass through the commands and to receive data.

It’s always the camera that initiates communication. In particular, it means that neither the tube, not the lens can “force” the camera to perform any action (for instance, to make a shot).

Normal dialogue between the camera and the lens consists of lens status queries and control commands.

In response to the status query, the lens communicates to the tube the data on its name, available aperture etc. If the camera display shows the aperture value of F0, it means that most likely the lens gave no response to the status query.

Control commands include changing focus, aperture etc.

The tube is being included in the process of communication between the camera and the lens and adds control commands for change of focus.

The tube watches the communication between the camera and the lens and tries to determine when the camera makes a shot. Usually there’s a certain sequence of commands that corresponds to this.
If the tube detects that a shot has been made, the led on the tube flashes green and the lens sends additional commands to the lens to shift focus.

The first sign is the aperture value on the camera display. The correct aperture value means at least that the tube does not interfere with the communication between the camera and the lens.

The second sign is the led on the tube flashing green at each shot. This means that the tube follows the camera commands, that it detected the required sequence and has sent additional command to the lens.

Sometimes the lens does not execute the focus change commands received from the tube. Here are some of the known reasons:

1. The step value is too small and the internal mechanics of the lens are not capable to make it. In general, every lens has such a minimum step that it can make without fail. Some lenses get stuck only at one particular point. Most likely, it happens due to the wear of parts or their contamination. In such cases, it’s better to set a big step and decrease gradually. If you put your ear to the lens you will be able to hear if the lens makes steps or not.
2. The lens is set to manual focusing. Not all of the lenses, but some ones ignore focusing commands when set to Manual Focusing mode. For instance, original Canon lenses can execute such commands, while third-party lenses for Canon cameras can’t. That’s why for original lenses you should use the configuration method 2, and for the third-party ones – configuration method 3
3. Focusing range on the lens does not correspond to the current focusing distance. Some macro lenses have several focusing ranges. For instance, if the switch is set to 0.38-0.55m, while the lens is being actually focused at 3 m distance (according to the lens scale window), the lens may ignore focusing commands. Normally we’d recommend to set the switch to FULL, i.e. full focusing range.
4. The lens has no internal focus motor. Some lenses for Nikon cameras support autofocus, but has no built-in motor (e.g. AF-D), totally relying on the camera motor. Of course, the lens can’t execute focusing commands. AF-D lenses that has a built-in motor exist, however, we have no proven information on compatibility with the tube.