ET vs AT

Choosing the Right Option for Your Optical System

When designing a fluorescence optical system, the filter set you choose plays a central role in determining image quality, signal strength, and channel separation. Small differences in filter design can significantly impact your results.

A fluorescence filter set is designed to selectively transmit excitation light to the sample and pass the resulting emission light to the detector, while blocking unwanted wavelengths. The quality of these transitions directly affects sensitivity and image clarity.

ET Filters

ET (Enhanced Transmission) filters are our highest-performance option, manufactured using a modified magnetron sputtering process that produces durable coatings with high transmission (typically 93–97%) and steep spectral edges. They are optimized for maximum signal throughput, excellent blocking with zero bleed-through between excitation and emission light, and the most demanding imaging applications. All ET sets are sub-pixel image-registered by design, making them ideal for multicolor experiments where precise spatial alignment across channels is critical. Choose ET filters when your application requires the highest possible signal intensities, zero-pixel-shift image registration, or when working with challenging or closely spaced fluorophores.

AT Filters

AT filters provide durable sputtered coatings with greater than 90% transmission and excellent out-of-band blocking, offering a robust and cost-effective solution for routine fluorescence applications. They are well-suited for standard detection tasks and assays where accurate color discrimination is needed but the ET series' extreme sensitivity is not required. Choose AT filters when performing routine fluorescence detection or assays, when accurate color discrimination is the priority, and when strong performance with cost efficiency matters.

Overview of ET and AT Filter Sets

	AT Filter Sets	ET Filter Sets
Purpose	Routine fluorescence detection and assays	Highest performance fluorescence imaging
Transmission	>90%	93-97% (typically)
Image Registration	Standard	Zero-pixel-shift, sub-pixel registered
Best For	Accurate color discrimination, general applications	Maximum signal intensity, demanding multicolor imaging
Cost	Cost-efficient	Premium

Table of Key Terms

Term	Meaning
AT	Magnetron-sputtered exciter, barrier/emitter, or dichroic (typically 45° AOI); recommended for basic visual applications such as cell culture
ET	Magnetron-sputtered exciter or barrier/emitter, typically normal incidence (0° AOI) for maximum performance
LP	Longpass filter (0° AOI) is designed to transmit (pass) longer wavelengths of light while actively blocking or attenuating shorter wavelengths.
M	Barrier/emission filter used primarily in fluorescence applications to isolate the specific light emitted by a target sample while aggressively blocking the much brighter excitation light
SP	SP stands for Shortpass. A shortpass filter or dichroic transmits (passes) all light with wavelengths shorter than a specific cutoff wavelength, while blocking or reflecting all longer wavelengths
T	Magnetron-sputtered dichroic (typically 45° AOI); recommended for maximum performance; also transmittance measures the percentage or fraction of incident light that successfully passes through the filter (often expressed as %T)
X	Excitation filter
XR	Extended reflection, typically 45° AOI
XRU	Extended reflection, including the UV, typically 45° AOI
XT	Extended transmission, typically 45° AOI
###	Wavelength in nanometers

For more in-depth definitions of the nomenclature used to name our filters, please see our comprehensive glossary page.

Conclusion

Both our ET and AT filter series are designed to deliver excellent fluorescence performance, but the right choice depends on your application’s specific demands. For the highest sensitivity, precise image registration, and maximum signal in challenging experiments, ET is the clear choice. For reliable, cost-effective performance in routine applications, AT delivers everything you need.

If you have questions about which filter set is right for your system, don’t hesitate to contact us. We’re here to help.

Frequently asked questions

Does it matter which dichroic I use with my excitation and emission filters?

Yes, the correct dichroic (or polychroic) mirror selection is very important. The job of the dichroic mirror is to reflect the excitation light to the sample and transmit the emission light to the detector.

Can I use a longpass filter as a dichroic?

No. All of our filter and dichroic designs are very angle-sensitive. Our emission filters are designed for a zero-degree angle of incidence (AOI) and dichroics are designed for a 45-degree AOI (unless otherwise specified). Changing this angle will drastically shift the spectral performance of the part.