Custom Optical Filters: A Buyer's Guide for OEM and Integrators

Optical filters are specified, not shopped. Unlike a gobo, nobody buys a dichroic filter because the listing looked nice — they buy it against a coating curve, a substrate, and a tolerance. Which means the supplier conversation is won or lost on how precisely you can describe the requirement, and how fast the supplier can come back with a real answer.

This guide covers what to specify, what drives cost, and the four numbers to send in your first email.

The five filter families, and what each is for

Each family has its own tolerance language. A "good" spec for an AR window is meaningless for a bandpass filter.

What to specify (the four numbers)

Suppliers can quote a price from almost nothing, but they cannot quote an accurate one. Send these four and the reply becomes a real specification instead of a question:

1. Substrate and thickness. BK7, B270, fused silica, sapphire, or soda-lime. Fused silica and sapphire survive high power and harsh environments; BK7 is the economical default. Thickness is not cosmetic — it shifts the optical path and affects wavefront error.

2. Dimensions and tolerance. Diameter or rectangular size, plus tolerance (±0.1 mm is common). Square-cut windows with tight corner tolerances cost more than round.

3. Optical specification. For a bandpass: center wavelength, bandwidth (FWHM), and blocking range. For AR: the wavelength range and target reflectance per surface. For a mirror: reflectivity at the design angle, and the angle range.

4. Quantity and surface quality. Scratch-dig (e.g. 60-40 or 40-20) and quantity. Surface quality and quantity move price more than any other pair of parameters.

A first email containing these four gets a technical reply. An email saying "we need an optical filter, please quote" gets a request for the same four — and a week lost.

What drives the price

Coating complexity. A single-layer AR is inexpensive. A 40-layer dichroic stack is not. Every additional layer is deposition time and yield risk.

Tolerance. Tightening wavelength tolerance from ±10 nm to ±2 nm typically costs 30–100% more, because yield drops.

Substrate. Sapphire and fused silica cost multiples of soda-lime, and large-format fused silica is often on lead time.

Size. Cost scales faster than area. A 100 mm window is not 4× a 50 mm window — handling and coating uniformity push it higher.

MOQ. Small runs carry setup cost per batch. This is where a factory-direct supplier differs most from a catalog distributor: MOQ is negotiable, and small prototyping runs are possible.

Prototype first, then scale

The failure mode in custom optics is ordering production quantity against an unverified design. Recommended sequence:

1. Specification review — send the four numbers, get feasibility and a coating curve

1. Prototype run — 5–20 pieces, measure, iterate

1. Production — quantity pricing after the design is proven

Skipping step 2 is how projects end up with 5,000 parts that miss the spec by one parameter.

Quality documentation to ask for

• Coating curve / transmission data for the delivered batch, not a generic datasheet

• Inspection report — dimensions, scratch-dig, coating adhesion

• Environmental test results if the part goes outdoors or into a medical device

• RoHS / REACH declarations for consumer products

If a supplier cannot provide batch-level data, they are trading, not manufacturing.

Two adjacent categories worth knowing

Beauty device filters follow the same rules but with a consumer-safety overlay: IR/UV cut specifications matter for skin-contact devices, and documentation requirements are stricter.

Laser protective lenses are a safety component, not a convenience one. Specify the wavelength, the optical density required, and the power level — and never substitute a general-purpose filter for a rated protective window.

Frequently asked questions

What is the minimum order for custom filters? Prototype runs from small quantities are usually possible with a factory-direct supplier. Production pricing typically starts to improve meaningfully above a few hundred pieces.

Can you match an existing filter's performance? Yes, if you can supply the transmission curve or the original part's specification. Send a sample if documentation is unavailable.

How long does a custom coating run take? Prototypes in 1–2 weeks; production typically 3–5 weeks depending on coating complexity and substrate availability.

Do you provide coating curves with the shipment? Yes, batch-level transmission data on request.

Have a specification to quote?

Send substrate, dimensions, optical spec, and quantity — we will return feasibility, a coating curve, and prototype pricing. sales@gobofactory.com / WhatsApp +86 13456752363.