Optical Filters FAQs

Here we have provided comprehensive lists of commonly asked questions regarding our 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 Fluidics, Cameras, Microfluidics, our Webstore, and Engineering Partnership.


Understanding filter, substrate, and housing thickness

understanding filter substrates

Semrock offers two categories of individual catalog sized filters: unhoused filters such as dichroic beamsplitters, mirrors and tunable filters, or housed filters mounted in black anodized aluminum housings. Housed filters include bandpass filters, edge filters, and some dichroic beamsplitters.  For an unhoused filter, the unmounted filter thickness and unmounted substrate thickness are identical.  For a housed filter, the mounted filter thickness and unmounted substrate thickness are different, because the mounted filter thickness is the same as the housing thickness. 

Each housed filter is available in one standard filter (housing) thickness, either 3.5 mm or 5.0 mm. The 3.5 mm housed filters are typically used as emitters when part of a filter set; the 5.0 mm filters are most commonly used as exciters when part of a filter set.  The 3.5 mm thick housings can accommodate substrate thicknesses ranging from 1.05 mm to 2.0 mm; the 5.0 mm thick housings, from 1.05 mm to 3.5 mm.

The size of each filter mounted in a housing as a standard catalog configuration is shown on the Specifications tab (see below) under Physical Filter Specifications as “Transverse Dimensions (Diameter)”. 

specifications tab on product page

Take for example the exciter and emitter filters from the GFP-3035D general-purpose filter set. The FF02-472/30-25 Exciter is mounted in a 5.0 mm aluminum housing, as shown below.

filter thickness mounted example 1

The FF01-520/35-25 Emitter is mounted in a 3.5 mm aluminum housing, as shown below.

filter thickness mounted example 2

For dichroic beamsplitters and other unmounted filters in a catalog configuration, the size of the filter in the Specifications tab is shown as “Transverse Dimensions (L x W)”.

As shown below, the FF495-Di03-25x36 dichroic beamsplitter of the GFP-3035D filter set has dimensions 25.2 mm x 35.6 mm, has a substrate thickness of 1.05 mm and is unmounted.

substrate thickness example

Find information about filter thickness, whether mounted or unmounted, unmounted substrate thickness, and dimensional tolerances of filter and substrate thicknesses in the Physical Filter Specifications section of the Specifications tab.

physical filter specifications for a BrightLine® single-band bandpass filter


The thickness of a custom sized, unmounted circular or rectangular filter refers to the substrate thickness.

Semrock catalog filters are coated on substrates with standard thicknesses 0.5 mm, 1.05 mm, 2.0 mm, 3.0 mm, 3.5 mm, and 6.0 mm; each product family is coated on one specific thickness.  Before purchase be sure to verify the filter thickness and whether that will be suitable for mount and application requirements.

For questions about filter, substrate or housing thickness, please contact our Semrock optical filters team.