New-Tech Europe | April 2018

e.g. sensor and lens, need to be stable against any environmental influence. The most common variables are expansion and contraction of the camera system due to temperature changes, shock, and vibration. One or more parameters can be more critical, depending on the system scenario. A stereo system with a larger baseline distance, for example, is more sensitive to temperature changes, due to the increased expansion of the larger mass. Conversely, vibration is more of an issue with smaller systems that might be mounted on robots. Lens manufacturers provide different design and material solutions to meet these needs with their lenses. The stable setup of the lens mount and sensors rests with the camera manufacturer. Nevertheless, an evaluation of system requirements and the precise matching of all components is necessary to guarantee an optimal result. Design Requirements Lens parameters, and especially the mechanical design of the lens, need to be adapted for stereo vision applications. Usually, C-mount lenses have moving parts, including a variable aperture and a focusing unit. The more sophisticated high-resolution lenses utilize a full floating design. Normally, the focus and aperture can be set by locking screws. However, depending on the design of the lens, "locked" parts can “shift” in environments with sufficient shock and vibration. Under these circumstances, a lens can lose focus, or have the aperture affected. Even if the fixing screws prevent defocusing or a major change in aperture, stereo systems are more sensitive to small

Figure 1: Stereo system: The baseline distance between the two sensors, and the alignment are fixed

changes that are not considered an issue with single camera solutions. Just as the lens elements can be moved for adjustment, they cannot be completely fixed to the housing that is still subject to subtle

movements. Also, stability depends on the number of screws and the screw types; for example, pan-head screws are more stable than knurled screws due to the increased locking force that can be applied to them.

Figure 2: In a standard lens, all lens elements move backward and forward. In a floating design, single lens elements or groups of lens elements move towards each other. C-mount lenses typically have fixing screws for the iris and focus

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