MTF data could reflect the optical system performance, and a proper optical testing lab setup is essential for obtaining reliable, repeatable MTF result. Shape Optics has prepared and setup MTF Optical test lab for an fluorescent detection system in Singapore. Here we could like to share some tips and experience. Hope it will help you.
And before configuring the lab with MTF charts and equipment, consider the following:
To obtain precise MTF measurements, the optical test lab should be set up in a space with little ambient lighting such as an interior, windowless room. Walls should be painted neutral middle gray (N5) to black, using a matte, flat, or eggshell wall paint to minimize reflected light. Reflective surfaces, such as polished metal or white/light colored surfaces, should be minimized. All additional light sources, including room lights, windows, doorways to other rooms, and LED indicators on equipment, should be covered or eliminated while conducting tests
Clear Acrylic Mounting for Transmissive Testing
Always wear clean, white cotton gloves when handling a test chart to prevent damage and blemishes. Store the chart in a low-heat, low-humidity environment away from direct sunlight. To ensure accurate and repeatable MTF measurement results, use a professionally mounted chart as well as a mounting system that enables precise alignment of the chart and lens. It is strongly recommended that charts be mounted on a smooth flat surface, like an acrylic board, to ensure no blemishes, bends, or bubbles occur that negatively impact image quality measurements. Check that the chart and camera system are level relative to one another. The MTF measurement chart need not be level with the ground if it is level with the device. If the environment allows, it is acceptable to test the device pointed down with the chart on a floor or table; e.g., with a microscope
Optical test lab Equipment
Shape Optics propose a solution for setting up a professional MTF measurement- optical test lab as below
Optical test lab lighting setup
Arrange lighting equipment for even, glare-free illumination. Lighting angles should be between 35° and 45° . Avoid placing any lighting behind the lens or at angles greater than 45° because doing so can cause glare and cast shadows on the test chart. Angles less than 20° can cause issues with texture and lighting uniformity. It is beneficial to have light modifiers to reduce flare light. Orienting the reflective light fixtures vertically allows for even illumination by keeping light levels consistent from the bottom to the top of the MTF measurement test chart. For detailed lighting arrange information, please check the digraph as below.
Matte charts are ideally suited for avoiding glare under most MTF measurement test scenarios. Glare in the outer patches of a test chart can ruin measurements and hard to avoid in semigloss charts. If you use semigloss charts, reduce glare by decreasing the angle between the lights and the chart, but verify the illumination levels remain consistent.
Lighting Uniformity Requirements
Lighting uniformity in the MTF measurement is strongly affected by the distance and orientation of the light source. To measure uniformity, think of the chart like a grid, and check the illuminance level in each grid square. Start by checking the center square, then each corner and side. You may also check the illuminance levels at each key feature of the MTF measurement chart. You should have no more than 20% variance in uniformity over the entire chart for SFR/MTF and distortion measurements, where small portions of the target are analysed and exposure is not critical. Uniformity with only ±5% variance or better is required for accurate tonal and colour measurements.