Biconcave Lens - Bote Optics Singapore Singapore

Biconcave Lens – Precision Diverging Lenses for Optical Applications

What is a Biconcave Lens?

A biconcave lens, also known as a double concave lens, has two inward-curved (concave) surfaces. It is a diverging lens that spreads incoming parallel light rays outward, forming virtual, upright, and reduced images. Biconcave lenses are commonly used in laser beam expansion, optical instruments, and image reduction systems.

At Bote Optics, we provide custom-manufactured biconcave lenses with a focus on precision, coating versatility, and rapid global delivery.

Key Specifications – Biconcave Lens

Parameter	Specification Range
Material	BK7, Fused Silica, Sapphire, CaF₂, ZnSe
Diameter	5 mm – 100 mm (custom sizes)
Focal Length	-10 mm to -500 mm
Thickness Tolerance	±0.1 mm
Surface Quality	40-20 or 20-10 scratch-dig
Coating Options	Uncoated, AR, UV, VIS, NIR, IR
Surface Accuracy	λ/4 to λ/10

Need a biconcave lens for high-power IR lasers or broadband AR coatings? Request a custom quote.

Double Concave Lens Definition

A double concave lens is a type of lens with both surfaces curved inward. It is classified as a negative lens due to its diverging property. This lens is used to spread light rays apart, which makes it useful in reducing optical aberrations, controlling beam diameter, or creating virtual images.

Double Concave Lens Ray Diagram

In a ray diagram of a biconcave lens:

Parallel rays diverge after passing through the lens.
Their extensions appear to originate from the focal point on the same side as the incoming light.

Image: Double Concave Lens Ray Path – Divergence of Incident Parallel Rays

Double Concave Lens Uses

Application	Purpose
Beam Expansion Systems	Widening laser beams
Optical Systems Alignment	Reducing focal shift and distortion
Imaging Systems	Minimizing magnification
Ophthalmic Equipment	Vision testing & correction
Microscopy & Projection Devices	Adjusting focal planes

Engineers at Bote work closely with customers to optimize biconcave lenses for specific system integration.

Double Concave Lens Image Characteristics

Type of Image: Always virtual
Orientation: Upright
Size: Reduced
Image Position: On the same side as the object

This makes biconcave lenses essential for systems that require non-inverted, smaller images such as VR optics and laser projectors.

Focal Length of Double Concave Lens

The focal length fff of a biconcave lens is negative and is calculated using the lensmaker’s formula: 1f=(n−1)(1R1−1R2)\frac{1}{f} = (n – 1)\left(\frac{1}{R_1} – \frac{1}{R_2}\right)f1=(n−1)(R11−R21)

For a symmetrical biconcave lens: f=−R2(n−1)f = \frac{-R}{2(n – 1)}f=2(n−1)−R

Where:

RRR = Radius of curvature (negative for concave surfaces)
nnn = Refractive index

Tip: Contact Bote for help selecting the right focal length based on your optical path length and divergence angle.

A Hollow Double Concave Lens?

While most double concave lenses are solid glass or crystal, some experimental or fluidic systems use hollow lenses (filled with gases or liquids) to simulate unique refractive environments. Bote focuses on high-stability, solid optics with robust coatings for laser-grade use.

Biconcave vs Plano Concave Lenses

Feature	Biconcave Lens	Plano Concave Lens
Surface Design	2 concave surfaces	1 flat, 1 concave surface
Divergence Power	Higher	Lower
Aberration Balance	Symmetrical	Asymmetrical
Preferred Use	Beam expansion	Collimated beam divergence

Learn more about Plano Concave Lenses

Double Concave Lens – Price Overview

Diameter (mm)	Material	Uncoated (USD)	AR Coated (USD)
12.7 mm	BK7	$6 – $12	$10 – $18
25.4 mm	Fused Silica	$15 – $30	$25 – $40
50.8 mm	Sapphire	$60 – $100	$80 – $140

Need IR-compatible biconcave lenses (e.g., ZnSe, Ge)? Let us know your wavelength range!

FAQs – Biconcave Lenses

Q1: How do you define a concave lens?
A: A concave lens is a diverging lens with at least one inward-curved surface. It spreads incoming light rays and forms virtual images.

Q2: What’s unique about a double concave lens image?
A: The image is always virtual, upright, and smaller than the object. Ideal for image reduction applications.

Q3: What is a hollow double concave lens used for?
A: These are used in fluid optics or experimental setups where refractive index control is needed dynamically.

Q4: Can I get a biconcave lens with custom coatings?
A: Yes, at Bote, we offer custom AR coatings for UV, VIS, NIR, and IR ranges.

Q5: How do I choose between plano concave and biconcave?
A: If you need symmetrical divergence and better spherical aberration control, go with biconcave.