Band-pass filters only transmit a certain wavelength band and block others. The width of such a filter is expressed in the wavelength range it lets through, and can be anything from much less than an Ångström to a few hundred nanometers. Such a filter can be made by combining an LP and an SP filter.

All-pass filter

Conventional LensesIn conventional lenses, the entrance and exit pupils are not located at infinity, so the chief rays will not be parallel to the optical axis. In this case, the magnification of the object depends on its distance from the lens and its position in the field of view. Figure 4 above shows an example ray trace through a conventional camera lens; notice how the chief rays are angled with respect to the optical axis in both image and object space. Note that both Figures 3 and 4 feature the same lens design; only the aperture stop location was varied to shift the bi-telecentric system to a non-telecentric one.

Andover offers one of the broadest ranges of hard-coated narrowband filters in the industry. Our filters feature very high transmission and dense blocking from UV-1200nm. They are suitable for high-temperature applications.

High-pass filter

By tailoring the blocking range to match the detector, we can provide the maximum possible throughput while maintaining good blocking to meet the customer’s needs. Wavelengths include all popular laser, mercury biomedical, and analytical spectral lines. All filters are constructed using the same high-quality materials and methods as our standard bandpass filters, thus providing a highly stable, long-lasting filter.

Our exceptionally high level of stock, and unique processing methods, allow us to ship most items within two days after receipt of an order. If required, rush orders can usually be shipped within one day. All out-of-stock items will be shipped within two weeks after receipt of a purchase order.

For an image space telecentric lens, the chief rays will be parallel to the optical axis on the image's side of the lens (image space). This is accomplished by setting the aperture stop at the back focal plane of the lens, which results in an exit pupil at infinity. Since the chief rays must pass through the center of the exit pupil, the chief rays on the image side of the lens must be parallel to the optical axis. An example of an image space telecentric lens is shown in Figure 2.

Optical Bandpass filter

Thorlabs offers its own line of bi-telecentric lenses for machine vision applications. These lenses offer magnification in both image and object space that is independent of distance (within the depth of field) or the position in the field of view. This attribute is ideal for machine vision applications: when measuring dimensions, a telecentric lens will yield the same measurement regardless of changes in object distance or position. For more details on telecentric lenses and their differences from standard lenses, please see the Telecentric Tutorial tab above.

Bandpass filters are defined by three critical features: Center Wavelength (CWL)—the wavelength at the center of the passband. Full Width at Half Maximum (FWHM)—the bandwidth at 50% of the maximum transmission. Peak Transmission (T)—the wavelength of maximum transmission

Example ImagesFigures 5 and 6 show photographs taken with a bi-telecentric lens and a standard camera lens, respectively. With the telecentric imaging system, the height of the two screws appears to be the same, even though the object planes are separated by approximately 45 mm along the optical axis. With the conventional imaging system, the two screws appear to be different heights, which could result in inaccurate dimensional measurements. A machine vision system using a bi-telecentric lens can offer advantages for dimensional metrology. For example, these lenses can be integrated into our Multi-Sensor Video Measurement Machines.

Andover also offers a first-surface variant of its standard UV bandpass filter. The coatings are deposited on a single surface of a UV-grade Fused Silica substrate and include a hard-oxide overcoat for protection. See more at: UV Bandpass Filters for Sterilization

Optical bandpass filters are designed to transmit a well-defined band of energy in the electromagnetic spectrum. Andover offers one of the most extensive listings of standard "off-the-shelf" interference filters in this industry. We have a range of wavelengths range from the ultraviolet through the near-infrared and include many of the primary laser, mercury, biomedical and analytical spectral lines. Standard sizes include 12.5mm Ø, 25.0mm Ø, and 50.0mm Ø. All Andover filters are mounted in black anodized metal rings which provide an added measure of protection against chipping, scratching, and high humidity conditions. In addition, all filters have their part number permanently engraved on their edge and each filter is supplied with a calibrated spectral bandpass data curve at no-charge. Custom spectral data is available and will be quoted upon request. Shorter wavelengths, longer wavelengths, and custom shapes & sizes are available.

Bandpass filters are one of the simplest and most economical ways to transmit a well-defined band of light and to reject all other unwanted radiation. Their design is essentially a thin film Fabry-Perot Interferometer formed by vacuum deposition techniques and consists of two reflecting stacks, separated by an even-order spacer layer. Each one of these structures is referred to as a cavity, and some filters may contain as many as eight cavities. There are many different variations of the Fabry-Perot type bandpass filter, but for this discussion, we will only consider the all-dielectric and metal-dielectric types.

Andover’s Standard Bandpass filters have been the mainstay of the industry for decades. With our proprietary stabilization and sealing method, these filters will generally last for 10-20 years in the field. Their longevity, coupled with their low cost and ready availability, make these a great choice for most applications.

Lowpassfilter

Band passfilter circuit

Please note that users must take care to properly mount and support the MVBT2313 lens due to its size and weight; this lens should not be solely mounted by its C-mount threads.

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In order to make it simple for customers to custom- tailor a bandpass filter for their application, Andover offers a line of Semi-Custom bandpass filters. Their construction is similar to both the Standard Bandpass and High-Transmitting bandpass filter offerings. We offer a wide selection of wavelengths, bandwidths, and sizes, and offer two blocking options.

This line of hard, first-surface coated filters was designed to cover the standard Raman spectroscopy lines. They feature very high transmission over a broad range about the wavelength of interest.

For an object space telecentric lens, the chief rays will be parallel to the optical axis on the object's side of the lens (object space). This is accomplished by setting the aperture stop at the front focal plane of the lens, which results in an entrance pupil at infinity. Since chief rays are directed towards the center of the entrance pupil, the chief rays on the object side of the lens will be parallel to the optical axis. An example of an object space telecentric lens is shown in Figure 1.

Types of Telecentric LensesIn order to achieve a telecentric lens design, all of the chief rays (rays from an off-axis point that pass through the center of the aperture stop) have to be parallel to the optical axis in either image space or object space, or both.

For a double telecentric, or bi-telecentric, lens, the front and back focal planes are made to overlap so that the aperture stop is located where both the entrance and exit pupils are at infinity. In a bi-telecentric lens, neither the image or object location will affect the magnification. Thorlabs' telecentric lenses are all bi-telecentric designs. Figure 3 shows an example ray trace through a bi-telecentric lens and illustrates how the chief rays pass through the system.

These graphs show the theoretically calculated distortion modeling results from Zemax. Each individual lens ships with a detailed test report showing the exact specifications and distortion plots for the lens, including RMS distortion, maximum distortion, magnification, maximum telecentricity, image size, and working distance. A sample report for each lens can be viewed on the Overview tab.

The all-dielectric type consists of two highly reflecting mirrors separated by a dielectric spacer layer. These reflecting mirrors are constructed of alternating high and low refractive index materials and the reflectance of the stack is sometimes in excess of 99.99%. By varying the thickness of the spacer layer and or the number of reflecting layers, one can alter the central wavelength and bandwidth of the filter. This type of filter displays very high transmission in the passband, but, has a limited range of out-of-band blocking. To compensate for this deficiency, an additional blocking component is added, which is either all-dielectric or metal-dielectric depending upon the required blocking range. This additional blocking component will eliminate any unwanted out-of-band radiation but it will also reduce the overall throughput of the filter.

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There are a number of variations of an optical bandpass filter’s construction, and each has its advantages. Andover offers a variety of options so that you can select the best-suited filter type for your application. The table below summarizes the major features of the various types of filters listed above, to aid in quickly locating the type that is best suited for your application. If you would like advice from our technical sales staff, please contact us at info@andcorp.com.

Butterworth filter

Each individual lens ships with a detailed test report showing the exact specifications and distortion plots for the lens, including RMS distortion, maximum distortion, magnification, maximum telecentricity, image size, and working distance. Sample reports are available in the table to the right. Raw data files are available upon request for each lens. These contain maps for distortion, absolute distortion, and telecentricity, as well as a measured data report. Graphs showing typical performance for distortion (%) vs. field height (mm) can be found on the Graphs tab above.

Telecentric lenses are designed to have a constant magnification regardless of the object's distance or location in the field of view. This attribute is ideal for many machine vision measurement applications, as measurements of an object's dimensions will be independent of where it is located.

These lenses are designed for 2/3" format sensors, such as those used in a variety of our scientific CMOS cameras. Sensors smaller than 2/3" can also be used but with reduced field of view. The lens housing features external C-mount (1.000"-32) threading on the image side of the lens, which is also compatible with many of our cameras. By using an SM1A10 thread adapter, the C-mount can be mated to internal SM1 (1.035"-40) threads for compatibility with our lens tubes or other SM1-threaded mounts. CS-Mount cameras are compatible with these lenses when using a CML05 CS- to C-Mount adapter.

The metal-dielectric type is similar to the all-dielectric type except that it utilizes a metal spacer layer instead of a dielectric layer. Although this type of filter has excellent out-of-band blocking and high passband transmission, it lacks the sharp cut-on and cut-off slopes of the typical two and three cavity filters. The metal-dielectric type is mainly used for bandpass filters in the ultraviolet. However, one version, the induced transmission type, is used as an additional blocking component when rejection is required to the far-infrared.

Optical bandpass filters are optical filters that pass one or more specified wavelength band(s) while blocking others. Bandpass filters are referred to by the wavelength range, also known as the passband, which they are designed to transmit. They are common filters suitable for a wide range of optical applications, including; environmental testing, colorimetry, flame photometry, fluorescence applications, UV sterilization, spectral radiometry, medical diagnostics, chemical analysis, machine vision, biotech instrumentation, medical devices, and laser line separation.

These bandpass filters are designed for use in situations where far-infrared blocking is not required. They feature high transmission in the passband region and good blocking over a limited range. Theoretical transmission curves are available on request.

Andover’s High-Transmitting Optical Bandpass filters are a variant of the Standard Bandpass filter line. Designed for use with PMTs and photodiodes, they employ only dielectric coatings and have a blocking range tailored to the detector. This results in higher transmission than their fully-blocked counterparts. For your convenience, the high-transmitting bandpass filters are listed in the Standard Bandpass section and are highlighted for easy identification.