Wells Research & Development

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Model OS400B - Large Aperture Lens Bench

OS400B PixelScope System OS400B
OVERVIEW
  • The OS400B is an automated lens bench, suitable for lenses whose aperture is as large as 100 mm
  • The OS400B can measure basic lens parameters such as focal length, pupil size, field curvature, distortion, color aberrations and chief ray angle.
  • The system can also make image quality measurements (MTF) at up to 1000 lines per mm.
  • The base OS400B is configured for testing at infinity. Options are available for testing at finite conjugates, and also for testing afocal instruments.
  • The OS400B is modular and exceptionally flexible. The image analysis microscope can be configured to pivot with the lens under test, or remain fixed relative to the optical rail.

Tips for Lens Designers:

The OS400B can display wavefront aberrations at the lens pupil and create "ray fan" plots.
USED TO
  • Validate lens prototypes for conformance to specification
  • Certify production lenses
  • Diagnose imaging problems
    • RANGE OF LENSES TESTED

    Lenses with clear aperture as large as 75 mm can be tested with the standard collimator. An optional collimator is available with 100 mm aperture.

    The included 20X microscope lens has an NA of 0.4, and is suitable for lenses as fast as F1.2

    The standard 1 meter rail is suitable for lenses with EFL up to 500 mm. Longer rails (up to 3m) are available.

    Several quick-change LED sources are included to cover the visible spectrum plus 780 nm. An optional halogen source permits work out to 1000 nm.

    PRINCIPLE OF OPERATION

    A small integrating sphere provides an exceptionally uniform back-light for the target reticle. A diffraction-limited collimator, with clear aperture of 80 mm (standard) or 100 mm (optional) forms a virtual image of the target.

    The lens under test forms a real image of the target. A diffraction-limited video microscope captures the image for analysis.
    AUTOMATION
    The motorized rotary stage is suitable for lenses weighing up to 10 kg.

    The motorized X and Y stages have total travel of 40 mm, with sub-micron precision.

    OPERATION MODES

    In fully automatic mode the system can capture hundreds of images in a minute or two, creating rich plots showing through-focus MTF, MTF vs FOV, field curvature. The underlying data can recalled at any time for review.

    In quick test mode the system visits a small number of field points, and rates the lens as pass / fail based on the performance criteria you have specified. Test times are typically under 10 sec.

    In manual mode the system can also be used as an ordinary lens bench, with manual control over the motors.

    MEASUREMENT PRINCIPLE

    The OS400B includes a selection of reticles, including a USAF target and black-on-white target for making veiling glare comparisons. However, most measurements are made with a simple “box” target whose sides are very narrow lines. Such a target permits simultaneous measurement of EFL and MTF.
    ACCURACY AND REPEATABILITY

    Unfortunately, MTF measurements have come to be viewed with suspicion by many in the industry, perhaps because of bad experiences with older systems. Wells Research is out to change this: The OS400B provides repeatable, traceable measurements you can have confidence in. Questions you should ask include the following:

    • Are the camera images representative of the lens under test or does the system itself add wavefront error?
      After all, the MTF calculation is just math, and will be accurate to many decimal places. However, the calculated MTF is only as valid as the image captured by the camera. Unless the image reflects the flaws of the lens under test, and only those, flaws, the calculated MTF will be of dubious value. The OS400B optics are diffraction limited, and an inspection certificate is included.
    • Has the operator correctly setup the system?
      In PixelScope, system parameters are entered into graphical pages to minimize the chance of operator error.
    • Is it possible to trace the MTF value to a known standard?
      The OS400B includes a certified “golden lens” for setup and verification. The OS400B can measure both MTF and 3-bar contrast. In the initial stages of an investigation you may wish to measure both and verify correlation. This provides increased confidence, and is another safeguard against operator setup error.
    • Is it possible to save the test images for later reference?
      The OS400B can optionally save every image to disk for future rererence.
    COMPUTER AND SOFTWARE

    The OS400B includes our “PixelScope-OpticStudio” software package. The system also includes a small form factor computer and monitor.

    LENS HOLDER

    The OS400B includes a small 3-jaw lens holder suitable for lenses up to about 40 mm diameter. The system also includes several uncommitted dovetail clamps for you construct holders optimized for your own large aperture lenses.

    TRAINING

    Please contact us to discuss setup and training.