Optical Filters FAQs

Here we have provided comprehensive lists of commonly asked questions regarding our Semrock optical filters and related applications. This information is designed to support your inquiries, but if you don’t find the answers you are looking for we encourage you to contact us for further assistance.

Please use the sort buttons in the left navigation to navigate between questions and answers that are specific to Optical Imaging Systems, Fluidics, Cameras, Microfluidics, our Webstore, and Engineering Partnership.


What is flatness / RWE classification?

Wavefront distortion can degrade image quality by reducing contrast or compromising resolution. In several microscopy applications, reducing wavefront distortion is critical to achieving the microscopy method.

IDEX Health & Science offers an extensive and industry-leading range of Semrock brand catalog filters for a variety of applications with specific Flatness / RWE needs. The Flatness Classifications listed in the table below provide an intuitive approach to selecting products of appropriate flatness for a given application.

In determining suitable flatness need for a given application, the most important parameter is often the diameter of the beam striking the dichroic beamsplitter surface. The table below shows the Semrock optical filters best suited to the application, for maximum diameter values. For more specific information, and for other beam diameter value and microscopy examples, the Technical Note and White Paper on this topic [1, 2] provide additional information on RWE, TWE, and microscopy methods, as well as guidance from a system designer’s perspective.

[1] Technical Note: Choosing Dichroic Beamsplitters with Flatness/RWE Appropriate to the Microscopy Method

[2] White Paper: Maximizing the Performance of Advanced Microscopes by Controlling Wavefront Error Using Optical Filters

Flatness/RWE Classification


Nominal Radius of Curvature

Maximum Reflected Beam Diameter, mm

Reflected Wavefront Error at 632.8 nm, PV

Dichroic Family and Example Part Numbers

Super-resolution / TIRF




~ 1275 meters


< 0.2λ

BrightLine® Laser (Di03-R405-t3-)

~ 255 meters


< 1λ

BrightLine® Laser (Di03-R405-t1-)



Splitting of emission signal on a pixel based detector


~ 1275 meters


< 0.2λ

BrightLine® Image-splitting


~ 100 meters


< 2λ

BrightlLine® Image-splitting (FF509-FDi01-)


Confocal, combining/splitting laser beams

~ 30 meters


< 6λ

BrightLine® Laser (Di02-R405-)

RazorEdge Dichroic (LPD02-488RU-)

LaserMux (LM01-503-)

StopLine® Notch Dichroic (NFD01-488-)

Standard Epi-fluorescence

Widefield fluorescence

~ 6 meters

Not Applicable

>> 6λ

BrightLine® (FF495-Di03-)