General Specifications

We produce OEM quantities of narrow and wide band interference filters, long and short pass filters, neutral density filters and other specialty filters. New techniques and processes have been developed to allow us to offer you beneficial pricing structures and performance standards that are unmatched in the optics industry. Sizes may range from a tenth of an inch square to eight inches in diameter. Standard sizes listed in this section of our site are ½”, 1″ and 2″ diameter.

Transmittance (T)

Also called “Transmission”, this symbol represents the conductance of radiant energy through the filter medium. It denotes the percentage of energy transmitted through the filter medium and is used to describe the filter’s efficiency within the pass band.

Out-of-Band Rejection

This is the degree of transmittance in the out-of-pass band area of the filters. Usually referred to as “blocking density” or simply “blocking”.

Optical Density (OD)

This is the unit of measure used to describe the ” blocking density” of the filter. It can be expressed as 10 to the power of transmittance. For example, an OD = 4, can be expressed as 10-4 transmittance, which means that transmittance peaks in the out-of-pass band do not exceed 0.01%. Formula: OD = log10 (1/T)

Bandwidth (FWHM)

Also called full-width-half-maximum. This is the width (in nm) of the pass band between the half-power points of transmittance.

Center Wavelength (CWL)

This is the center wavelength of the bandwidth and can be referred to as the average of the half-power wavelengths.

Dependency of CWL on Incident Angle

CWL shifts toward the short wavelength when the incidence angle of the radiant energy is tilted away from normal incidence. The following formula may be used to estimate such a shift:

CWL = CWL0 {1-(1/Ne)2sin2 q }0.5 

CWL0 : wavelength at normal incidence
CWL : wavelength at incidence angle
Ne : effective index of the filter
q : incidence angle

Temperature Effects

Our filters are specially formulated to withstand severe temperatures from -60°C to 70°C with a recommended temperature gradient with respect to time of 5°C/min. However, an increase in temperature can still shift the CWL as well as broaden the FWHM, or vice versa. Contact us for specific temperature coefficients.

Humidity Effects

While humidity does not affect spectral characteristics of filters, the mechanical strength and lifetime may be deteriorated when exposed to moisture. We recommend mounting filters in our black anodized aluminum housings for harsh operating conditions.

Reliability Testing Specifications

Surface Quality: 80/50
Rejection Range: X-ray to Far IR unless otherwise specified
Clear Aperture: > 80% of outside diameter
Size tolerance: +0/-0.5 mm
Thickness: < 6.4 mm
Abrasion: MIL-C-48497, para.
Adhesion: MIL-C-48497, para.
Cleanability: MIL-C-48497, para.
Humidity: MIL-STD-810E, Method 507.3, Procedure III

Band Shape

The shape of the pass band is a function of the number of cavities employed (see part number listings). The more cavities used results in a more rectangular shape, while less cavities results in a more triangular-like shape of the transmittance curve.


MK Photonics Inc. warrants all filters to be free from defects in material or workmanship
for a period of one year after delivery.