Mirror lenses/ reflecting lenses

Beck Optronic Solutions is proud to be the manufacturer of the Original Beck/Ealing Reflecting Objectives. Based on a two mirror system reflecting objectives were originally designed for microscopy in 1904.The all reflecting optics means that, in contrast to refracting objectives, they are totally free from chromatic abberations. The BOS objectives are based on the work of C. R. Burch, who in his 1947 paper, showed that by careful selection of the mirror curvatures and their separation, they are corrected for spherical abberation, coma and astigmatism, leading to diffraction limited performance. In addition to these corrections, reflecting objectives have the following advantages when compared to standard refracting microscope objectives:

  • longer working distance in terms of magnification
  • larger numerical apertures for higher light gathering performance
  • high throughput from UV to far IR
  • Peak to Valley wavefront error ≤ λ/4 (0.25 λ), λ/14 RMS @633nm
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Applications
  • 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
5001-0005002-0005003-0005004-0005006-0005007-000
Magnification x15x15x25x36x52x74
Numerical Aperture0.280.500.400.500.650.65
Focal length (mm)13.3513.418.005.413.552.54
Visual FOV (mm)1.201.200.720.500.340.24
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)24.523.214.58.61.91.0
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.

RangeReflectanceCoatingSuffix
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”.

Notes:

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.