Question 1

What is SearchLight and how do I use it?

Accepted Answer

SearchLight is a free spectral modeling tool, and there are many resources for understanding and learning how to use SearchLight.

Question 2

Which optical filter set is compatible with your fluorophore?

Accepted Answer

Use our Fluorophore Reference chart to match which optical filter sets are compatible with the fluorophore in your application.

Question 3

How do you clean optical filters?

Accepted Answer

1. Select cleanroom swab size. 2. Depress the fluid dispenser to flow cleaning fluid into the top, and touch the swab to the methanol (do not place swab directly into the fluid container). 3. Touch the swab to the cleanroom wipe to remove excess liquid. 4. Depending upon part size, apply swab to filter using a circular motion for round parts or an S-shaped motion for rectangular parts across the filter surface. It’s important to keep contact with the filter throughout this process. 5. Turn filter over and repeat. 6. Do not use the same swab side on the second filter side.

Question 4

What is the lifetime of edge blackening paint on a filter, and are there special methods to clean these filters?

Accepted Answer

The edge blackening paint is intended to remain adherent to the glass surface for the life of the filter, without decomposing and/or falling off, provided that the paint on the filter edge is neither abraded by an external agent nor dissolved using a chemical agent such as acetone. Examples of suitable use include being stably secured in an assembly or housing with no exposure to such solvents. Use isopropyl alcohol (IPA) or methanol to clean edge blackened filters, as these solvents don’t affect the edge blackening paint, provided the cleaning is gentle, i.e., not aggressive or of overly long duration. Do not use acetone, as this will remove the paint.

Question 5

How can my company check if a filter meets the cosmetic specification?

Accepted Answer

Each Semrock-brand optical filter shipped by IDEX Health & Science has been inspected and found to pass the relevant cosmetic specifications, using the ANSI or ISO 10110 inspection procedure as appropriate. If the customer wishes to check if a filter meets the cosmetic specification, it is again necessary to follow the applicable cosmetic inspection procedure. To check a limited number of filters for cosmetics, an RMA can be used to return the filters to the IDEX Health & Science production facility for inspection; the results of the inspection will be shared with the customer.

Question 6

What is angle tuning?

Accepted Answer

The spectrum of any thin-film filter shifts toward shorter wavelengths when the angle of incidence (AOI) of light upon the filter is increased from 0° (normal incidence) to larger angles. In most cases, the filter spectrum becomes highly distorted at larger angles, and the shift can be significantly different for s- and p-polarized light. The spectral shift that you experience is highly dependent upon filter design.

Question 7

What are AOI and CHA?

Accepted Answer

Angle of Incidence, or AOI, is the angle at which a collimated beam of light is incident on the filter's first surface, measured relative to the surface normal. Cone half-angle, or CHA, refers to the angular range associated with a non-collimated incident beam, and is measured from the AOI to the largest cone angle.

Question 8

What is ASCII Data?

Accepted Answer

ASCII data is typically a text file with two columns. The first column is the wavelength (measured in nanometers) and the second column is the corresponding transmission value of the filter at that wavelength.

Question 9

What is Clear Aperture?

Accepted Answer

For unhoused, round filters, the clear aperture is guaranteed to be greater than 85% of the outer diameter. For square and rectangular parts, the guaranteed clear aperture will be greater than 80% of the filter's transverse dimensions and is elliptically shaped. The clear aperture of a housed filter is dependent on the size and thickness of the housing ring. All filter specifications are guaranteed only within the clear aperture region.

Question 10

What is filter orientation?

Accepted Answer

To maximize intended transmission and blocking and to minimize autofluorescence, filters must always be oriented so that light is incident on a specific surface of the filter.

Question 11

What is flatness / RWE classification?

Accepted Answer

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. 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.

Question 12

What is optical density?

Accepted Answer

Optical Density (OD) is a convenient tool to describe the transmission of light through a highly blocking optical filter (when the transmission is extremely small). OD is defined as the negative of the logarithm (base 10) of the transmission, where the transmission varies between 0 and 1.

Question 13

What is pixel shift, and how does the Semrock ZERO option help?

Accepted Answer

Pixel shift results when a filter in an imaging path (the emitter and/or dichroic beamsplitter in a fluorescence microscope) deviates the light rays to cause a shift of the image detected on a high-resolution monochrome digital camera. This shift becomes problematic when two or more images of the same object are acquired using different filter sets and then overlaid to simultaneously view fluorescence from multiple fluorophores. Images produced by different fluorophores (and different filter sets) will not be accurately correlated or combined because each image is shifted by a different amount depending on the wedge angles found in each filter set. To eliminate pixel shift, BrightLine ZERO™ and Avant ZERO™ filter sets are manufactured and tested to exacting tolerances to ensure accurate image registration when combining multiple images.

Question 14

What is polarization?

Accepted Answer

When light is incident on an optical filter at a non-normal angle of incidence, the polarization of the light can be described by two orthogonal vector components associated with the orientation of the electric field of the light wave. The polarization is referenced to the “plane of incidence,” or the plane that is parallel to the normal to the surface of the filter and contains both the incident and the reflected light rays. The polarization component that is perpendicular to the plane of incidence is called the “s” component, and the component that is parallel to the plane of incidence is called the “p” component.

Question 15

What are limitations of conventional spectral measurement?

Accepted Answer

Commercially available spectrophotometers are optimized for specific scientific and industrial applications. Because their designs have been constrained by price and performance requirements, most commercial spectrophotometers have insufficient precision to accurately measure the spectral characteristics of high-performance optical filters, especially filters with steep spectral edges and deep blocking, which are Semrock hallmarks. Functional limitations in light sources, detectors, and diffraction gratings, and in their combined performance, can create artifacts in the spectral measurement of such high performance optical filters. A customer's filter spectrum measurement may differ from the measurement performed at Semrock due to the presence of these artifacts. Understanding the origins of such measurement discrepancies enables inference of the filter’s actual performance and provides guidance for decision making.

Question 16

What are Sutter threaded rings?

Accepted Answer

An integrated filter wheel mounting ring for optical filters that is threaded to match the openings in a Sutter filter wheel hub.

Question 17

What are wavenumbers?

Accepted Answer

The color of light is generally identified by the distribution of power or intensity as a function of wavelength. Sometimes it is convenient to describe light in terms of wavenumbers, where the wavenumber (w) is simply equal to the inverse of the wavelength and is therefore proportional to frequency. Wavenumbers are often used in Raman spectroscopy since the separation of a particular Raman line from the laser line is fixed by the molecular properties of the material and independent of which laser wavelength is used to excite the line. This means that the shift is of constant frequency, regardless of excitation wavelength and can be conveniently expressed in terms of wavenumbers.

Question 18

Can you combine two filters within an optical test set-up to achieve deeper blocking?

Accepted Answer

One way to combine two filters for deeper blocking is to slightly tilt the filters relative to each other. Interference filters reflect rejected light, so the slight tilt ensures the rejected light is reflected out from between the pair of filters.

Housing Thickness	Housing Diameter (mm)
Housing Thickness	12.5	25	32	50
3.5 mm	CA = 10 mm	CA = 22 mm	CA = 29 mm	CA = 45 mm
5.0 mm	CA = 10 mm	CA = 21 mm	CA = 29 mm	CA = 45 mm

FAQs

Optical Filters FAQs

What is Clear Aperture?