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Doublet Lens 4.7mmdia x 20mm F.L.

SKU: LDB2005
More Information
Focal Length (mm) 20
Diameter (mm) 4.7
Back Focal Length (mm) 18.25
Centre Thickness (mm) 3.6
Edge Thickness (mm) 3
Type Positive
Design Aperture (mm) 4.2

A single lens used to form an image will always show some chromatic aberration, that is variation of focal length with wavelength. Achromatic doublet lenses correct for this as they are constructed from two different glass types and designed to remove first order chromatic aberration. Generally spherical aberration is reduced at the same time. Achromatic doublets are widely used to form images, for example telescope objectives, and also to focus laser beams.

These quality achromats have been designed and optimised for performance and are available as positive and negative focal length types. We stock a full range of doublet lenses from small 3mm dia up to 110mm dia to meet a range of demanding applications. Typical applications where achromatic doublet lenses are used are imaging, analysers, fibre-optic lighting, laser range finders endoscopes and borescopes.

We can offer custom achromatic doublet lenses to meet your requirements or alternatively edge stock lenses for a quick turnaround, please enquire.

Typical Material:

Centring Accuracy:
Focal Length:
Surface Quality:
Flint (N/F2) or equivalent and Crown (BK7) or equivalent Flint (SF6) or equivalent and Crown (N-LAK22) or equivalent
+0.0 / -0.10mm
< 5 arcmin
± 0.1% (≤ 10mm) ± 1% (>10mm)
<40-20 scratch/dig

Mounting into lens cells.
Special AR coatings.
Cutting to special sizes.
Stock lenses can be edged to smaller diameters.

Flint element AR coated for high index in the visible:
Single layer MgF2 AR for high index, R.avg<0.2%@550nm 
Crown element AR coated for low index in the visible:
Single layer MgF2 AR, R.avg<0.2%@550nm 
Some combinations are coated with broadband multilayer AR coating for extended visible:
Broadband Multilayer AR, R.avg<0.5%@450-900nm