7.3 Lighting Strategy
Once the image has been properly focused and magnification has been set, adjust front lighting and back lighting using the on-screen sliders provided by M3 software. You can also utilize room lighting, or shield the system from room lighting, as appropriate. Correct lighting is paramount to accurate measurement with any video-based measurement system. A clear image with lighting toward the low side is recommended. Lighting that is too low will result in a dark, low-contrast image with indiscernible features. Lighting that is too bright can result in a washed-out image and in hot spots (blooms) that distort features. When adjusting lighting, start with light that is lower than desired, then increase lighting while viewing the image on the computer monitor. Maintain constant lighting for consistent results. Do not to change light levels between points used to measure the same geometrical feature. Depending on the part characteristics and the feature being measured, the right combination of lighting from the available sources can aid in bringing out a particular feature. Take time to experiment by balancing the available light sources. • Zoom optics come with a dedicated 64 millimeter (2.5 inch) diameter LED ring light for front illumination and a 50 millimeter (1.97 inch) diameter LED back light for silhouette illumination. The back light is built into the column at the front of the instrument and is collimated so that the emitted rays are parallel to the optical axis of the imaging lens. If glare develops on edges of convoluted, reflective parts, install a furnished aperture into the back light. This aperture limits the diameter of the illuminating lens. • Telecentric lenses from 0.3X to 4.0X use the same 50 millimeter (1.97 inch) diameter LED back light as the zoom optics, except that a neutral density filter is installed to reduce intensity. This is because telecentric lenses have greater light gathering capability. If there is a problem with glare, the same aperture as for the zoom optics can be installed for telecentric lenses with magnification greater than 0.8X. A polarizer is built into the ring light. The resulting polarizing ring light can be rotated in its mount to reduce the effects of room lights or reflections from convoluted parts. A dot on the edge of the polarizer normally points up to reduce the effects of room lights. • The 0.14X telecentric lens uses a dedicated 100 millimeter (3.9 inch) diameter collimated LED back light. A polarizer in a separate mount fits over the lens and can be rotated to reduce glare when necessary. A built-in LED coaxial illuminator is used for front lighting.
7.3.1 Aligning the Back Light
Aligning of the back light is required for optimal performance of telecentric lenses, as the emitted light must be parallel to the optical axis of the lenses. While alignment has been done at the factory, alignment might need to be repeated following shipment and installation at the user site.
To initiate realignment, perform the following steps:
1. Remove the cover of the column that holds the back light.
2. Find the three sets of push-pull screws that rotate the mount that holds the back light.
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