Clear Aperture(CA) of Optical Filters

When customers request optical filters from us , we usually ask the customer : What’s clear aperture do you require ?

So, what is clear aperture ?

The clear aperture is that area inside which all optically functional tolerances and specifications apply .The manufacturing process inevitably creates a lower-quality surface bear the edge than the center . The edge may also have low surface quality , figure , or chips .

In the below photo , the orange area is the Clear Aperture .

For an?optical filters , we can divide its surface into three areas .

1.?Optical area

2.?Coated area

3.?Clear aperture

Normally , Optical area (φ) > Coated area (φd) > Clear aperture (φe)

For example:

Circular : φ=24mm , φd=23mm , φe= 21mm

Square: 55×55 , 54×54 , 53×53

If customer has no special requirements, we usually consider the clear aperture according to more than 90% or 95% of the optical area .

For example : The customer requires an optical filter with dimensionφ50mm, then we will consider the clear aperture as φ48mm around

If customer requires full aperture , that means the optical area is equal to the clear aperture . We will achieve full aperture coating through processing technology .

For example: The customer requires an optical filters with dimension φ50mm , also requires clear aperture φ50mm . When we manufacture the optical filters , we will coat on a square glass 55×55 , then cut and grind into φ50mm .

Please note : When calculating the clear aperture , it must be calculated with the center of the optical filter symmetric outward , and the optical axis as the symmetry axis point .