How to Read an Optical Drawing: 10 Specifications Every Engineer Should Know
optical specifications
8/17/20262 min read
When requesting custom optical components, many engineers focus on the shape and material of the optic.
However, a complete optical drawing contains many critical specifications that determine optical performance, manufacturing difficulty, and final cost.
Understanding these parameters can help avoid communication problems and ensure the right component is produced.
Here are 10 important optical specifications every engineer should understand.
1. Material
The optical material determines key properties such as:
Transmission range
Refractive index
Thermal stability
Environmental resistance
Common materials include BK7, fused silica, sapphire, and optical glass.
Choosing the correct material depends on wavelength and application requirements.
2. Surface Quality (Scratch-Dig)
Surface quality describes visible imperfections on an optical surface.
Common specifications include:
60-40
40-20
20-10
10-5
Lower numbers indicate stricter requirements.
However, higher surface quality also increases manufacturing cost.
The correct specification depends on the application.
3. Surface Roughness
Surface roughness describes microscopic surface texture after polishing.
It is commonly expressed as:
Ra
RMS
Surface roughness is especially important for:
Laser optics
High-power applications
Precision imaging systems
4. Flatness
Flatness describes how much an optical surface deviates from an ideal plane.
Typical specifications:
λ/4
λ/10
Higher precision flatness is required for demanding optical systems.
5. Radius of Curvature
For lenses, radius of curvature directly affects optical power and focal length.
Small variations in radius can influence system performance.
6. Thickness Tolerance
Center thickness affects:
Optical path length
Focal position
Mechanical assembly
Tighter thickness control may be required in multi-element optical systems.
7. Diameter and Dimensional Tolerance
Dimensional tolerance determines how accurately the component fits into the mechanical structure.
Overly tight tolerances can increase cost without improving system performance.
8. Centration
Centration defines the alignment between the optical axis and mechanical axis.
Poor centration may cause:
Beam deviation
Image distortion
Alignment issues
It is especially important for laser and imaging systems.
9. Coating Requirements
Optical coatings control reflection and transmission.
Common coatings include:
AR (Anti-Reflection)
BBAR (Broadband AR)
HR (High Reflection)
A complete coating specification should include:
Wavelength range
Angle of incidence
Performance requirement
10. Clear Aperture and Wedge
Clear aperture defines the usable optical area.
Wedge describes the parallelism between two optical surfaces.
Both can influence:
Beam quality
Transmission
System alignment
Final Engineering Advice
A good optical specification is not the tightest specification possible.
It is the specification that achieves the required performance while balancing:
✔ Optical requirements
✔ Manufacturing capability
✔ Cost efficiency
Before sending an RFQ, understanding these key parameters can save time, reduce unnecessary cost, and improve communication with optical suppliers.
At Positive Optics, we support custom optical components including lenses, windows, filters, mirrors, prisms, and beam splitters with application-specific specifications.
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