Reflecting Objectives

Reflecting objectives are renowned for their unique optical properties. Beck Optronic Solutions is one of very few companies worldwide designing and manufacturing them.

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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 aberrations. The Beck 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 aberration, 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 distances relative to the magnification;
Large numerical apertures for improved light gathering power;
High throughput from UV to far infrared;
Coatings available to enhance performance at specific wavelength regions;

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Applications include conventonial microscopy and beam delivery systems. With their unique lack of chromatic aberrations they excel especially where a dual wavelength operations is required, such as alignment to a visible beam for working with an IR or UV beam laser. Other uses include:

Two-photon microscopy
FT-IR spectroscopy;
UV metrology and microscopy;
Semiconductor wafer inspection;
Photomicroscopy;
Photolithography;
Thin film measurements;
Laser beam delivery systems;
Laser drilling and etching;
Product marking;
Laser pumping;
Thermal imaging microscopy.

BOS Reflecting Objectives are available in six standard models as detailed below, or can be fully customised as required.

All BOS Reflecting Objectives are compliant with the requirements of RoHS directives 2002/95/EC, 2011/65/EU and 205/863.

PROPERTY	Beck Optronic Solutions Model No
	5001	5002	5003	5004	5006	5007
Magnification	x15	x15	x25	x36	x52	x74
Numerical aperture	0.28	0.50	0.40	0.50	0.65	0.65
Focal length (mm)	13.35	13.41	8.00	5.41	3.55	2.54
Visual FOV (mm)	1.20	1.20	0.72	0.50	0.34	0.24
Obscuration	25.0%	21.5%	22.5%	13.0%	17.5%	15.0%
Transmitted wavefront error	≤λ/4 P-V, λ/14 RMS @633 nm
Working distance (mm)	24.5	23.2	14.5	8.6	1.8	1.0
Small mirror diameter (mm)	7.30	13.40	6.30	5.60	4.60	3.35
User adjustment for tube-length and cover glass thickness	Fixed (factory set)	Fixed (factory set)	Fixed (factory set)	Yes	Yes	Yes
Range of cover glass thickness (mm)	0 – 3.0	0 – 3.0	0 – 3.0	0 – 1.0	0 – 1.0	0 – 1.0
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

The standard reflecting objectives are supplied with aluminium coated mirrors. This gives the widest spectral coverage from UV to far IR, but limits the objective to low power use only. In applications requiring high power, Beck offers alternative coatings as detailed below. For specialised applications we can provide other specialist coatings.

Range	Reflectance	Coating	Suffix
250 nm to 10 µm	89.0% average	Aluminium	-000
190 nm to 10 µm	>89.0%	DUV Enhanced Aluminium	-190
700 nm to 15µm	98.0%	Gold	-120

Note: Our 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 more diffraction but only has a 4 point flare pattern and some users prefer this. Add postfix 4 to part number for a 4 legged spider when you order (3 legs are supplied as standard).

Notes: If back reflections may be an issue in your application a matt black dimple can be ground into the secondary (smaller) mirror. Add postfix -D to the part number.

If you require a clearance hole through the secondary mirror please contact us to discuss the options available.