RFT & RFT-TEMP: Precision Optical Characterization Across Angles, Distances, and Temperatures

In the development of advanced vision systems—ranging from autonomous vehicles to aerial drones—ensuring the reliability and performance of camera optics is paramount. At Fourier Image Lab, we utilize two sophisticated systems developed by Yanding: the RFT (Rotational Focus Tester) and its thermally enhanced counterpart, the RFT-TEMP. These systems enable precise optical testing under controlled conditions, allowing for comprehensive evaluation of camera modules in various scenarios.

rft-temp. system overview

Understanding MTF and the Importance of Real-World Testing

Modulation Transfer Function (MTF) is a critical metric that quantifies how effectively a lens reproduces contrast from the physical world into a digital image. Particularly when derived from a slanted-edge target, MTF provides insights into the optical system's behavior, including aspects like blur, noise, and digital processing effects.

However, image sharpness is not a static attribute; it varies with distance, angle, lens alignment, manufacturing variations, and environmental factors such as temperature. Contrary to the notion of scale-invariance, real-world testing reveals that MTF can shift significantly with distance, especially in long-focus lenses. Capturing this variation through through-focus curves is essential for understanding and optimizing lens performance across different depths.

Style reference - Fourier Lab reporting MTF density from RFT *(1)

Simulating Real-World Distances with Collimators

To replicate various object distances without the impracticality of physical setups, we employ collimators—optical devices containing internal targets and lenses. By moving a slanted-edge target within the collimator tube, we simulate virtual distances ranging from 0.4 meters to infinity. This approach allows for precise and repeatable testing of lens performance across different depths.

RFT optical core - robotic collimator

To ensure consistency and compliance with ISO 12233 standards, we have developed a proprietary alignment algorithm that automatically rotates the target inside the collimator, maintaining the slanted edge at a 5-degree orientation regardless of the collimator's rotation. This innovation guarantees valid and comparable MTF measurements across all field angles.

Automated Angular and Depth Scanning with RFT

The RFT system automates both angular and through-focus testing, featuring a rotating camera stage and a robotic arm that positions the collimator across various azimuth and elevation angles. Integrated with the MIG-S2 frame grabber, the system connects directly to MIPI, GMSL, and FPD-Link camera modules, facilitating synchronized frame capture and analysis.

This setup enables testing at any angle up to ±105° (210° total) and simulates virtual distances from 0.4 meters to infinity. The system's automation allows for the generation of comprehensive reports, including through-focus MTF curves, angular MTF surface plots, and distortion maps, all within approximately 15 minutes.

RFT System components

Evaluating Image Quality Across Temperatures with RFT-TEMP

Building upon the capabilities of the RFT, the RFT-TEMP system incorporates a temperature-controlled chamber to assess camera performance under thermal stress. This is particularly valuable for applications involving rapid environmental changes, such as drones ascending into cooler air or vehicles transitioning between varying temperatures.

The RFT-TEMP operates within a temperature range of -40°C to +125°C, with heating and cooling rates of 6–7°C/min and 3–4°C/min, respectively. Due to the protective glass interface, the system's rotational range is limited to ±70° (140° total). Despite this limitation, it provides sufficient coverage for most automotive, robotic, and industrial imaging systems.

​RTF (basic version)

Delivering Comprehensive Optical Analysis

Both RFT and RFT-TEMP systems offer a suite of capabilities, including automated acquisition of MTF, LSF, SFR, and PSF measurements across various field points. They generate precise surface maps, through-focus MTF at each angular field, and distortion analyses for wide-angle, fisheye, and telephoto optics.

Our measurements adhere to the latest ISO 12233:2023 standards, employing polynomial fitting and Tukey windowing techniques. Additionally, we have developed proprietary methods to compute high-accuracy MTF on RAW images without demosaicing, enhancing resolution fidelity in optical assessments.

RTF report

Furthermore, the systems facilitate the calculation of optical centers, ensuring proper alignment between lenses and sensors. They also enable the generation of 3D PSF clouds, supporting simulation, synthetic training, and lens digitization efforts.

Collaborate with Fourier Image Lab

At Fourier Image Lab, we operate both RFT and RFT-TEMP systems in our Campbell, California facility. We offer services including on-demand testing and digitization of lenses or cameras, report generation and validation for product teams, installation of RFT equipment at client labs or production lines, and sensor interfacing via the universal frame grabber.

For more information or to request a demonstration, please contact us at timo@fourierimagelab.com.

Reference 1*: The Architecture of the Human Fovea

Helga Kolb, Ph.D., Ralph F. Nelson, Ph.D., Peter K. Ahnelt, Ph.D., Isabel Ortuño-Lizarán, Ph.D., and Nicolas Cuenca, Ph.D.