Reflecting objectives

The original Beck/Ealing reflecting objectives were originally developed for microscopy and are only offered by a few manufacturers worldwide. They are based on a two-mirror system and, unlike refractive objectives, are free of chromatic aberration. The reflecting objectives are a combination of mirror and lens and consist of primary and secondary mirrors for light focusing and image formation. Originally developed for microscopy, the reflective lenses are now commonly used in beam delivery systems. They have unique optical properties and advantages compared to standard lenses:

  • Free of chromatic aberration
  • Longer working distance in relation to magnification
  • Larger numerical apertures for higher light gathering performance
  • High transmission power from the UV to far into the IR (various coatings available)
  • Low peak to valley wavefront error ≤ λ/4 (0.25 λ), λ/14 RMS @633nm
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    • FT-IR spectroscopy
    • UV Measurement and Microscopy
    • Semiconductor wafer inspection
    • Photomicroscopy
    • Photolithography
    • Thin film measurements
    • Laser beam guidance
    • Laser drilling and etching
    • Product label
    • Optical laser pumping
    • Thermal imaging microscopy

    Technical data of the standard models:

    PropertyBeck Optronic Solutions Model No
    Magnification x15x15x25x36x52x74
    Numerical Aperture0.280.500.400.500.650.65
    Focal length (mm)13.3513.418.005.413.552.54
    Visual FOV (mm)
    Obscuration25.0 %21.5 %22.5 %13.0 %17.5 %15.0 %
    Transmitted wavefront error≤ λ/4 P-V, λ/14 RMS @663nm≤ λ/4 P-V, λ/14 RMS @663nm≤ λ/4 P-V, λ/14 RMS @663nm≤ λ/4 P-V, λ/14 RMS @663nm≤ λ/4 P-V, λ/14 RMS @663nm≤ λ/4 P-V, λ/14 RMS @663nm
    Working distance (mm)24.523.
    Small mirror diameter (mm)7.3013.406.305.604.603.35
    User adjustmendt for tubelength & cover glass thicknessFixed (factory set)Fixed (factory set)Fixed (factory set)YesYesYes
    Range of cover glass thickness0 - 3.0mm*0 - 3.0mm*0 - 3.0mm*0 - 1.0mm0 - 1.0mm0 - 1.0mm
    Range of Tube-length (mm)80 - ∞*80 - ∞*80 - ∞*90 - ∞120 - ∞120 - ∞
    * Factory Set for one cover glass thickness and one tube length. To be specified at the time of ordering.

    Customer-specific adaptations of a mechanical nature or e.g. vacuum suitability are possible, in some cases only with low extra costs.

    As standard, the reflecting objectives are supplied with aluminium-coated mirrors. This ensures the widest spectral coverage from UV to IR. The objective is limited with regard to the usable performance. For applications requiring high power, the manufacturer offers alternative coatings, see table. Special coatings can also be offered for very special applications.

    250nm - 10µm89.0% averageAluminium-000
    190nm - 10µm>89.0%DUV Enhanced Aluminium-190
    700nm - 15µm98.0%Gold-120

    The standard objectives have a 3 legged spider (to support the secondary mirror) which minimises diffraction but produces a six point flare pattern.

    A “4 legged spider” produces a larger diffraction but at the same time produces a light reflex pattern with only 4 dots, which is sometimes preferred by users. Without specification the standard is always delivered with “3 legged spider”.


    If back reflections may be an issue in your application a matt black dimple can be ground into the secondary (smaller) mirror. If you require a clearance hole through the secondary mirror please contact us to discuss the options available.