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Infinity-Corrected Tube Lenses
Widefield Tube Lens,
Laser Scanning Tube Lens,
Widefield Tube Lens, f = 180 mm, 400 - 750 nm
Laser Scanning Tube Lens,
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Widefield imaging tube lenses take the collimated light from an infinity-corrected microscope and focus it onto a camera, as shown on the left. Laser scanning tube lenses can be used in telecentric systems to scan a laser spot across a sample.
These infinity-corrected tube lenses are designed for use with infinity-corrected objectives from all major manufacturers, including the dry, oil immersion, and physiology microscope objectives sold by Thorlabs. Designed for high-resolution imaging, biomedical, machine vision, and laser scanning applications, these lenses can be aligned in pairs to create relays, combined with objectives to create different effective magnification ratios at a scientific camera, used as drop-in replacements for tube lenses in existing systems, or integrated into DIY Cerna® Microscopes and other home-built microscopy setups to generate high-quality images.
Standard Widefield Tube Lenses
Telecentric Tube Lenses for Laser Scanning and Widefield Imaging
Our standard widefield tube lenses for the visible wavelength range can also be used for laser scanning purposes when paired with the CLS-SL visible scan lens for example. However, using a standard tube lens in a scanning configuration will limit the unvignetted field size, since the tube lens must be placed at the telecentric pupil distance from the objective (e.g., 250 mm for the TTL200 lens), rather than the intended pupil distance of the tube lens.
Microscope and Objective Optical Compatibility
Alternatively, objectives and tube lenses with different design focal lengths may be combined to create different magnification ratios at the camera without compromising the axial color correction. We offer four tube lenses with non-standard focal lengths that can be used to change the magnification of an existing system. To calculate the system magnification for different tube lens and objective combinations, see the Magnification & FOV tab.
Tube Lenses for Widefield Imaging
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This schematic shows the working distance and pupil distance for the TTL series and ITL200 tube lenses. The working distance corresponds to the distance from the top surface of the housing to the image plane. The pupil distance, defined as the distance between the bottom edge of the tube lens housing and the entrance pupil of the objective, can be set anywhere within the range specified in the table above, since the rays from the objective are in parallel bundles. If the tube lens is too close or far, the image may suffer from aberrations.
The TTL200 and ITL200 tube lenses should be inserted with the M38 x 0.5 threading facing the objective, while all other standard widefield tube lenses are engraved with an arrow next to an infinity symbol (∞) to indicate which side of the lens should face the objective (infinity space), as shown in the diagram above.
Tube Lenses for Laser Scanning and Widefield Imaging
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This schematic shows the TTL200MP Tube Lens in a laser scanning configuration with the working distance and pupil distance called out. The working distance corresponds to the distance from the edge of the housing below the engraving to the intermediate image plane. The pupil distance is defined as the distance between the edge of the tube lens housing above the engraving and the entrance pupil of the objective.
These lenses are engraved with an arrow next to an infinity symbol (∞) to indicate which side of the lens should face the objective (infinity space), as shown in the diagram above.
When viewing an image with a camera, the system magnification is the product of the objective and camera tube magnifications. When viewing an image with trinoculars, the system magnification is the product of the objective and eyepiece magnifications.
Magnification and Sample Area Calculations
The magnification of a system is the multiplicative product of the magnification of each optical element in the system. Optical elements that produce magnification include objectives, camera tubes, and trinocular eyepieces, as shown in the drawing to the right. It is important to note that the magnification quoted in these products' specifications is usually only valid when all optical elements are made by the same manufacturer. If this is not the case, then the magnification of the system can still be calculated, but an effective objective magnification should be calculated first, as described below.
To adapt the examples shown here to your own microscope, please use our Magnification and FOV Calculator, which is available for download by clicking on the red button above. Note the calculator is an Excel spreadsheet that uses macros. In order to use the calculator, macros must be enabled. To enable macros, click the "Enable Content" button in the yellow message bar upon opening the file.
Example 1: Camera Magnification
Example 2: Trinocular Magnification
Using an Objective with a Microscope from a Different Manufacturer
Magnification is not a fundamental value: it is a derived value, calculated by assuming a specific tube lens focal length. Each microscope manufacturer has adopted a different focal length for their tube lens, as shown by the table to the right. Hence, when combining optical elements from different manufacturers, it is necessary to calculate an effective magnification for the objective, which is then used to calculate the magnification of the system.
The effective magnification of an objective is given by Equation 1:
Here, the Design Magnification is the magnification printed on the objective, fTube Lens in Microscope is the focal length of the tube lens in the microscope you are using, and fDesign Tube Lens of Objective is the tube lens focal length that the objective manufacturer used to calculate the Design Magnification. These focal lengths are given by the table to the right.
Note that Leica, Mitutoyo, Nikon, and Thorlabs use the same tube lens focal length; if combining elements from any of these manufacturers, no conversion is needed. Once the effective objective magnification is calculated, the magnification of the system can be calculated as before.
Example 3: Trinocular Magnification (Different Manufacturers)
Following Equation 1 and the table to the right, we calculate the effective magnification of an Olympus objective in a Nikon microscope:
The effective magnification of the Olympus objective is 22.2X and the trinoculars have 10X eyepieces, so the image at the eyepieces has 22.2X × 10X = 222X magnification.
Sample Area When Imaged on a Camera
When imaging a sample with a camera, the dimensions of the sample area are determined by the dimensions of the camera sensor and the system magnification, as shown by Equation 2.
The camera sensor dimensions can be obtained from the manufacturer, while the system magnification is the multiplicative product of the objective magnification and the camera tube magnification (see Example 1). If needed, the objective magnification can be adjusted as shown in Example 3.
As the magnification increases, the resolution improves, but the field of view also decreases. The dependence of the field of view on magnification is shown in the schematic to the right.
Example 4: Sample Area
Sample Area Examples
The images of a mouse kidney below were all acquired using the same objective and the same camera. However, the camera tubes used were different. Read from left to right, they demonstrate that decreasing the camera tube magnification enlarges the field of view at the expense of the size of the details in the image.
Damage Threshold Data for Thorlabs' Tube Lens for UV Wavelengths
The specifications to the right are measured data for Thorlabs' TTL200-UVB Tube Lens.
Laser Induced Damage Threshold Tutorial
The following is a general overview of how laser induced damage thresholds are measured and how the values may be utilized in determining the appropriateness of an optic for a given application. When choosing optics, it is important to understand the Laser Induced Damage Threshold (LIDT) of the optics being used. The LIDT for an optic greatly depends on the type of laser you are using. Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). Pulsed lasers, on the other hand, often strip electrons from the lattice structure of an optic before causing thermal damage. Note that the guideline presented here assumes room temperature operation and optics in new condition (i.e., within scratch-dig spec, surface free of contamination, etc.). Because dust or other particles on the surface of an optic can cause damage at lower thresholds, we recommend keeping surfaces clean and free of debris. For more information on cleaning optics, please see our Optics Cleaning tutorial.
Thorlabs' LIDT testing is done in compliance with ISO/DIS 11254 and ISO 21254 specifications.
The photograph above is a protected aluminum-coated mirror after LIDT testing. In this particular test, it handled 0.43 J/cm2 (1064 nm, 10 ns pulse, 10 Hz, Ø1.000 mm) before damage.
According to the test, the damage threshold of the mirror was 2.00 J/cm2 (532 nm, 10 ns pulse, 10 Hz, Ø0.803 mm). Please keep in mind that these tests are performed on clean optics, as dirt and contamination can significantly lower the damage threshold of a component. While the test results are only representative of one coating run, Thorlabs specifies damage threshold values that account for coating variances.
Continuous Wave and Long-Pulse Lasers
When an optic is damaged by a continuous wave (CW) laser, it is usually due to the melting of the surface as a result of absorbing the laser's energy or damage to the optical coating (antireflection) . Pulsed lasers with pulse lengths longer than 1 µs can be treated as CW lasers for LIDT discussions.
When pulse lengths are between 1 ns and 1 µs, laser-induced damage can occur either because of absorption or a dielectric breakdown (therefore, a user must check both CW and pulsed LIDT). Absorption is either due to an intrinsic property of the optic or due to surface irregularities; thus LIDT values are only valid for optics meeting or exceeding the surface quality specifications given by a manufacturer. While many optics can handle high power CW lasers, cemented (e.g., achromatic doublets) or highly absorptive (e.g., ND filters) optics tend to have lower CW damage thresholds. These lower thresholds are due to absorption or scattering in the cement or metal coating.
Pulsed lasers with high pulse repetition frequencies (PRF) may behave similarly to CW beams. Unfortunately, this is highly dependent on factors such as absorption and thermal diffusivity, so there is no reliable method for determining when a high PRF laser will damage an optic due to thermal effects. For beams with a high PRF both the average and peak powers must be compared to the equivalent CW power. Additionally, for highly transparent materials, there is little to no drop in the LIDT with increasing PRF.
In order to use the specified CW damage threshold of an optic, it is necessary to know the following:
Thorlabs expresses LIDT for CW lasers as a linear power density measured in W/cm. In this regime, the LIDT given as a linear power density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size, as demonstrated by the graph to the right. Average linear power density can be calculated using the equation below.
The calculation above assumes a uniform beam intensity profile. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right).
Now compare the maximum power density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately. A good rule of thumb is that the damage threshold has a linear relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 10 W/cm at 1310 nm scales to 5 W/cm at 655 nm):
While this rule of thumb provides a general trend, it is not a quantitative analysis of LIDT vs wavelength. In CW applications, for instance, damage scales more strongly with absorption in the coating and substrate, which does not necessarily scale well with wavelength. While the above procedure provides a good rule of thumb for LIDT values, please contact Tech Support if your wavelength is different from the specified LIDT wavelength. If your power density is less than the adjusted LIDT of the optic, then the optic should work for your application.
Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. The damage analysis will be carried out on a similar optic (customer's optic will not be damaged). Testing may result in additional costs or lead times. Contact Tech Support for more information.
As previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. Pulsed lasers often do not heat the optic enough to damage it; instead, pulsed lasers produce strong electric fields capable of inducing dielectric breakdown in the material. Unfortunately, it can be very difficult to compare the LIDT specification of an optic to your laser. There are multiple regimes in which a pulsed laser can damage an optic and this is based on the laser's pulse length. The highlighted columns in the table below outline the relevant pulse lengths for our specified LIDT values.
Pulses shorter than 10-9 s cannot be compared to our specified LIDT values with much reliability. In this ultra-short-pulse regime various mechanics, such as multiphoton-avalanche ionization, take over as the predominate damage mechanism . In contrast, pulses between 10-7 s and 10-4 s may cause damage to an optic either because of dielectric breakdown or thermal effects. This means that both CW and pulsed damage thresholds must be compared to the laser beam to determine whether the optic is suitable for your application.
When comparing an LIDT specified for a pulsed laser to your laser, it is essential to know the following:
The energy density of your beam should be calculated in terms of J/cm2. The graph to the right shows why expressing the LIDT as an energy density provides the best metric for short pulse sources. In this regime, the LIDT given as an energy density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size. This calculation assumes a uniform beam intensity profile. You must now adjust this energy density to account for hotspots or other nonuniform intensity profiles and roughly calculate a maximum energy density. For reference a Gaussian beam typically has a maximum energy density that is twice that of the 1/e2 beam.
Now compare the maximum energy density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately . A good rule of thumb is that the damage threshold has an inverse square root relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 1 J/cm2 at 1064 nm scales to 0.7 J/cm2 at 532 nm):
You now have a wavelength-adjusted energy density, which you will use in the following step.
Beam diameter is also important to know when comparing damage thresholds. While the LIDT, when expressed in units of J/cm², scales independently of spot size; large beam sizes are more likely to illuminate a larger number of defects which can lead to greater variances in the LIDT . For data presented here, a <1 mm beam size was used to measure the LIDT. For beams sizes greater than 5 mm, the LIDT (J/cm2) will not scale independently of beam diameter due to the larger size beam exposing more defects.
The pulse length must now be compensated for. The longer the pulse duration, the more energy the optic can handle. For pulse widths between 1 - 100 ns, an approximation is as follows:
Use this formula to calculate the Adjusted LIDT for an optic based on your pulse length. If your maximum energy density is less than this adjusted LIDT maximum energy density, then the optic should be suitable for your application. Keep in mind that this calculation is only used for pulses between 10-9 s and 10-7 s. For pulses between 10-7 s and 10-4 s, the CW LIDT must also be checked before deeming the optic appropriate for your application.
Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. Contact Tech Support for more information.
 R. M. Wood, Optics and Laser Tech. 29, 517 (1998).
Thorlabs offers nine infinity-corrected tube lenses for widefield imaging. All TTL series lenses can provide diffraction-limited performance about any single wavelength from 240 to 700 nm (for the TTL200-UVB) or from 400 to 2000 nm (for all other TTL series lenses), provided that the tube lens is set to focus on the camera at the target wavelength. Please note that using these lenses for laser scanning will result in vignetting and uneven spot sizes over the FOV; for integration into a telecentric laser scanning system, see the tube lenses below.
The TTL200-UVB tube lens features an air-spaced design for superior performance and high power handling. It is AR coated for UV wavelengths (240 - 360 nm) and is designed to be used with our high-power MicroSpot® focusing objectives. The tube lenses coated for visible wavelengths (350 - 700 nm) offer good performance at shorter wavelengths (<480 nm) to accommodate applications using 405 nm and 443 nm illumination. The TTL200-B is AR coated for NIR wavelengths (650 - 1050 nm), making it ideal for NIR fluorescence and NIR DIC imaging. The TTL200-S8 utilizes a broadband MgF2 single-layer coating with a low transmission roll-off throughout the visible and NIR, with peak transmission centered at 830 nm. See the graphs in the table below for transmission data. Some TTL series lenses can be custom coated with an AR coating optimized for transmission within the design wavelength range; contact Tech Support for details.
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The three thread configurations available on our Widefield Imaging Tube Lenses are shown here with the objective-facing side down. Thead information for each item # is provided in the table below.
With the exception of the TTL200 and the ITL200, all of these tube lenses are engraved with an arrow next to an infinity symbol (∞) to indicate which side of the lens should face the objective (infinity space). Item #'s TTL200 and ITL200 should be inserted with the M38 x 0.5 threading facing the objective.
The TTL200 and ITL200 lenses have external M38 x 0.5 threading for direct compatibility with Nikon and Thorlabs microscopes. This threading can be converted to external SM2 (2.035"-40) threading using the SM2A20 adapter available below. Alternatively, the WFA4111 dovetail adapter, also available below, directly accepts a TTL200 or ITL200 tube lens, allowing it to be integrated with a Cerna microscope. We also offer the WFA4110 dovetail adapter, which is a version of the WFA4111 with the TTL200 tube lens built-in.
The rest of these lenses feature external SM2 (2.035"-40) threading on both sides that connects to our Ø2" lens tubes and many elements of our 60 mm cage system. To integrate one of these tube lenses with Thorlabs' Cerna® DIY Microscopy Systems, use the SM2M05 lens tube to connect to the WFA4111 Dovetail Adapter (available below).
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The TL600-A, TL400-A, TL300-A, TTL200MP, and TTL200MP2 tube lenses are designed to have the same track length, defined as the distance between the image plane of the tube lens and the shoulder of the objective.
These infinity-corrected tube lenses feature a telecentric design appropriate for both laser scanning and widefield imaging applications. Our laser scanning tube lenses with a wavelength range from 400 to 700 nm or 450 to 1100 nm can be paired with our SL50-CLS2 (450 - 1100 nm) scan lens to create a telecentric system. Similarly, the TL200-2P2 and TL200-3P tube lenses are designed to be used with our SL50-2P2 (680 - 1300 nm) and SL50-3P (900 - 1900 nm) scan lenses, respectively. Due to the extended wavelength range of their AR coatings, the TTL200MP and TTL200MP2 can be paired with any of these three scan lenses. The TTL200MP tube lens provides higher transmission at visible and NIR wavelengths, while the TTL200MP2 tube lens provides higher transmission at longer wavelengths approaching 2000 nm; see full transmission data by clicking the graph icon in the table below.
These tube lenses are engraved with an arrow next to an infinity symbol (∞) to indicate which side of the lens should face the objective (infinity space). The TL600-A, TL400-A, TL300-A, TTL200MP, and TTL200MP2 tube lenses are designed with the same nominal track length of 420 mm, allowing tube lenses of different focal lengths to be interchanged without realigning the imaging device or objective.
Some of these lenses can be custom coated with an AR coating optimized for transmission within the design wavelength range; contact Tech Support for details.
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A WFA4111 can be used to integrate a TTL200 tube lens into a custom epi-illumination module on a DIY Cerna Microscope.
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The WFA4111 adapter allows M38 x 0.5-threaded tube lenses to be easily integrated with Cerna microscopes and SM2-threaded components.
Thorlabs offers two styles of adapters for use with the externally M38 x 0.5-threaded TTL200 and ITL200 tube lenses, allowing them to be integrated with Thorlabs' SM2 lens tube systems and Cerna DIY Microscopy Platform. Our other tube lenses already have external SM2 (2.035"-40) threads.
Our WFA4111 Dovetail Adapter directly accepts the TTL200 and ITL200. Alternatively, external SM2 threads on the top of the adapter allow externally SM2-threaded lenses to be connected via an SM2M05 lens tube. The bottom of the adapter features a male D1N dovetail, making it compatible with our DIY Cerna systems. The SM2 threads on top can also be used to integrate user-designed camera tubes constructed from SM2-threaded lens tubes.
The SM2A20 allows the TTL200 and ITL200 to be easily converted to SM2 threading, enabling the construction of an optical system consisting of a scan lens and a tube lens using Thorlabs' standard SM2 lens tube components and the SM2-threaded GCM102(/M) 2D galvo mounting adapter. We also offer SM2-threaded adapters for common objective threads.
The SM38RR retaining ring can be used to lock the tube lens in place when using either adapter. We also offer the WFA4110 Dovetail Adapter, a version of the WFA4111 adapter that includes the TTL200 tube lens.