Precision Optics
Precision Optical FlatsHonestly measured.
Classically pitch-polished fused silica flats from a U.S. manufacturer with 25 years of precision etalon heritage. Reference and test flats in standard sizes, in stock, and priced below the catalog houses.
Reference-grade flats, manufactured the same way every time. Each flat is individually finished by our continuous pitch polishing process and measured power-included across the full clear aperture, then matched to a part number you can reorder. The specification you read is the surface you receive.
What you get
Four reasons buyers switch to Lunt
Pitch-polished surfaces
Classical continuous pitch polishing, refined over 25 years of etalon work. Low mid-spatial-frequency error, low scatter.
Power-included spec
Flatness reported with curvature included, the honest, stricter number. The figure on paper is the surface in your hand.
In stock, ships now
Eight standard sizes and tolerances held in inventory, ready for immediate deployment to your bench.
Made in the USA
Finished and measured in-house, priced below the catalog houses. Built to be bought, not just admired.
In stock
First Surface Flats
Single surface, uncoated, measured power-included. Eight standard sizes and tolerances, in stock and ready to ship.
| Part number | Diameter | Flatness (P-V) | Price | |
|---|---|---|---|---|
| O-025-FS-010-U | 25 mm | λ/10 | $120.00 | View |
| O-025-FS-020-U | 25 mm | λ/20† | $175.00 | View |
| O-050-FS-010-U | 50 mm | λ/10 | $205.00 | View |
| O-050-FS-020-U | 50 mm | λ/20† | $275.00 | View |
| O-075-FS-010-U | 75 mm | λ/10 | $395.00 | View |
| O-075-FS-020-U | 75 mm | λ/20† | $525.00 | View |
| O-100-FS-010-U | 100 mm | λ/10 | $695.00 | View |
| O-100-FS-020-U | 100 mm | λ/20† | $840.00 | View |
All flats measured power-included at 632.8 nm (HeNe). † λ/20 pricing is provisional pending production yield confirmation. Larger diameters and tighter tolerances available to order. Contact us for a quote.
Why Lunt
How we polish, and how we measure
Two things separate a Lunt flat from a catalog flat: how the surface is made, and how it is measured. Both are choices most suppliers make the easy way.
01 The craft
Classical pitch polishing
Every Lunt flat is finished by classical continuous pitch polishing, the same method we have refined over 25 years of building precision Fabry-Perot etalons for solar telescopes. Pitch polishing produces an inherently smooth surface with very low mid-spatial-frequency error.
It takes longer than automated sub-aperture figuring, but it yields a surface that performs in use, not just on a spec sheet. For applications where scatter and surface structure matter, that difference is real.
02 The metrology
Power-included measurement
Surface flatness can be reported two ways. Power-removed measurement mathematically subtracts the overall curvature of the surface, which makes the published number look better than the surface actually is. Power-included measurement reports the total deviation, curvature and all. It is the honest, stricter number.
We specify our flats power-included. When you buy a Lunt λ/10 flat, the λ/10 figure already includes any curvature. Same spec on paper. A measurably better optic in your hand.
The question to ask any supplier
When a flat is labeled λ/10, ask whether that figure was measured power-removed or power-included. The answer determines whether the specification is real.
Same number, different surface
The power-included difference
Two suppliers can print the same flatness figure and ship measurably different optics. The measurement method is the reason.
Power-removed, common in catalogs
λ/10*
The flattering number
Software subtracts the overall curvature of the surface before reporting. The published figure looks tighter than the optic actually is. The asterisk most buyers never see.
* curvature removed before measurement
Power-included, how Lunt specifies
λ/10
The honest number
Total surface deviation, curvature and all. When you buy a Lunt λ/10 flat, the λ/10 already includes any power. Stricter to meet, truer to use.
measured at 632.8 nm, full clear aperture
The line
Specifications
Shared across all eight single-surface flats. Individual product pages list the diameter and flatness for each SKU.
Material
Fused silica
Construction
Single surface, one polished reference face
Surface flatness
λ/10 or λ/20 P-V, measured power-included
Surface quality
Better than 60-40 scratch-dig, typical
Surface roughness
Below 0.020 wave RMS, typically far better
Clear aperture
90% of diameter
Secondary surface
Fine ground to suppress back-surface reflection and fringing
Coating
Uncoated
Edges
Protective bevel as needed, fine ground edges
Wavelength reference
632.8 nm (HeNe)
Packaging
Protective storage case included
Origin
Finished and measured in the United States
Where they work
Applications
Lunt optical flats serve as reference and test surfaces wherever flatness must be verified or used as a known standard.
Metrology laboratories
Surface-flatness standards for research and metrology labs that need a known reference.
Optical shops & QC
Reference and test flats for production quality control and incoming inspection.
Universities & photonics
Reference surfaces for university optics groups and photonics research.
Laser systems
Reference and beam-folding flats for laser benches and optical-path setups.
Astronomy instrumentation
Autocollimation and optical-path reference surfaces for telescope makers.
Custom requirements
Larger diameters and tighter tolerances available to order. Tell us what you need.
Our foundation
Decades of optical innovation
Lunt was founded by Andy Lunt, an optical engineer who launched Lunt Solar Systems and built it into the world leader in solar telescope etalons and filters. That work demanded surfaces flat and smooth enough to resolve sub-angstrom detail in the Sun.
These optical flats come from the same bench and the same hands. The pitch-polishing craft we refined for high-finesse etalons now produces standalone reference flats, finished and measured in the United States, and priced to be bought, not just admired.
25+
Years of etalon
polishing heritage
λ/10
Power-included
flatness, in stock
USA
Finished and
measured in-house
90%
Clear aperture
across the line
How it is made
From blank to bench
Every flat moves through the same four steps, the same way we build etalon substrates. No shortcut stages, no sampled inspection.
STEP 01
Select the blank
Fused silica blanks are graded and the reference face is generated for the target diameter.
STEP 02
Pitch polish
Classical continuous pitch polishing brings the surface to figure with very low mid-spatial-frequency error.
STEP 03
Measure power-included
Each flat is interferometrically measured power-included across the full clear aperture at 632.8 nm.
STEP 04
Pack and ship
The flat is matched to its part number and shipped in a protective storage case, ready to deploy.
Good to know
Questions, answered
What does power-included measurement mean?
It means the flatness figure reports total surface deviation, including the overall curvature (power) of the surface. Power-removed measurement subtracts that curvature first, which makes the number look tighter than the optic is. Our published figure already includes any power, so the spec on paper is the surface you receive.
What is included with each flat?
Each flat ships in a protective storage case and is matched to its part number for easy reordering. Flats are single surface, uncoated, with one polished reference face and a fine-ground secondary surface to suppress back-reflection.
Can I reorder the exact same specification later?
Yes. The part number encodes diameter, material, flatness, and coating, so reordering the same surface is a matter of quoting the same code. The scheme extends cleanly as new sizes and options come online.
Do you offer larger diameters or tighter tolerances?
Larger diameters and tighter tolerances are available to order. Tell us your application and target specification and we will quote a build. Use the request-a-quote link on this page.
What wavelength are the flats measured at?
All flatness figures are measured at 632.8 nm, the HeNe laser line, across 90% of the diameter (the clear aperture).
Custom orders
Need a size or spec not listed?
Larger diameters and tighter tolerances are available to order. Tell us what your application needs and we will quote it.
Start a custom order
Request a quoteMade in the USA · Built for optical excellence