Our team is ready to assist you!
Application Notes | Articles | EO Tech Tools | FAQs | Glossary | Marketing Literature | Video Resources
The information required to design with our lenses is provided with each lens listing in both our printed and online catalog. A detailed downloadable file of the prescription data for all the TECHSPEC® lenses that are available in our catalog, can be found on our Prescription Data page. If you have any questions regarding this information, you can always speak to one of our engineers.
Dust is the most common contaminant and can usually be removed using compressed air. If more cleaning is necessary, hold the lens in lens tissue and apply a few drops of reagent-grade isopropyl alcohol, reagent-grade acetone, or lens cleaning solution.
After blowing off dirt and dust with compressed air, the Drag Method of cleaning can be used to remove fingerprints or other contaminants. In the Drag Method, lens tissue saturated with reagent-grade isopropyl alcohol or reagent-grade acetone is slowly dragged across the surface. If done correctly, the solvent will evaporate uniformly without leaving streaks or spots.
Filters can be cleaned using the same methods as lenses or mirrors. The preferred method is to use compressed air or an air blower to remove dust.
Special care must be taken when cleaning gratings or wire-grid polarizers. Because the grooves are very tiny and delicate, the Drag Method is not recommended. The only recommended cleaning method is to use compressed air or an air blower to remove surface dust. Avoid methods that require any direct contacting of the grating surface. Ultrasonic cleaning should not be used as it may separate the grating surface from the glass substrate.
De-ionized water rinse, followed by a forced air drying. Wipe gently with lens tissue soaked with methanol, followed with a forced clean air or nitrogen drying. Note: Holographic diffusers are resistant to methanol and methylene chloride.
View Cleaning Optics for more in-depth information.
Micro optics are extremely small and should be handled with extra care due to their small size. For example, micro lenses are typically classified as lenses smaller than 3mm in diameter. Delicate tweezers may be used to securely hold a micro optic by its edge, or a vacuum pick-up tool to secure it in place for cleaning. Compressed air or an air blower may be used to safely remove surface dirt; cotton-tipped swabs or lens tissue saturated with reagent-grade isopropyl alcohol, reagent-grade acetone, or de-ionized water is effective in removing smudges. Ultrasonic cleaning is not recommended as it may scratch the delicate micro optics.
View Cleaning Optics for more in-depth information.
Edmund Optics® offers a variety of substrates for UV and IR applications, including BK7, fused silica, sapphire, calcium fluoride, zinc selenide, silicon, germanium and magnesium fluoride. These substrates are available on many of our stock lenses, windows and a host of other optics.
BK7 is a low cost substrate for visible and NIR applications. It is generally not favored for UV, though it offers good transmission down to 350nm. It is great for machine vision, microscopy, and industrial applications.
Fused silica has a low coefficient of thermal expansion and excellent transmission from UV to IR. It is great for interferometry, laser instrumentation, spectroscopy, and industrial applications.
Sapphire is extremely hard and durable with good transmission from UV to IR. It is great for IR laser systems, spectroscopy and rugged environmental equipment.
Calcium fluoride has low absorption and high damage threshold from 0.2 – 7μm. It is great for spectroscopy, semiconductor processing, and cryogenically cooled thermal imaging.
Zinc selenide has a low absorption coefficient and high resistance to thermal shock. It is great for CO2 laser systems and thermal imaging.
Silicon is a low cost and low density substrate for weight sensitive IR applications. It is great for spectroscopy, mid-IR laser systems, and THz imaging.
Germanium has a high index of refraction and knoop hardness with transmission in the mid and far-IR regions. It is great for thermal imaging, FLIR, and rugged IR applications.
Magnesium Fluoride is extremely rugged and durable with excellent broadband transmission from the DUV to mid-IR regions. It is great for UV and IR laser systems, rugged environmental equipment, and high vibration environments.
Laser Diode Cans are the simplest commercial packaging for laser diodes. They consist of the actual diode, a photodiode for monitoring output, and the can that holds them. Unfortunately, there is no single “best” lens to focus or collimate their output. Lasers diodes pose special challenges because their outputs are irregularly shaped (elliptical rather than circular) and vary widely amongst the on the market. It is difficult to compensate for these factors with a single lens and therefore the best lens will depend on the specifications of one’s laser diode (e.g. the beam divergence in each axis) as well as the desired beam characteristics (e.g. desired spot size and distance). In many cases, the desired results can only be obtained with multiple elements. Luckily, if the main concern is beam quality without the need for a custom multiple-element solution, Edmund Optics® offers many Laser Diode Modules and other packaged diode lasers that come with the diode and integrated optics to maximize the quality of the beam.
Germanium is fairly non-reactive except with strong oxidizing agents. Both high temperatures and high vacuums can cause germanium to react with ethanol, but under normal conditions, ethanol and acetone are both safe to use on our germanium, including any of the lenses and windows that Edmund Optics® provides.
Germanium itself isn't hazardous. Sometimes, Thallium is used in manufacturing infrared materials and as a coating layer on them. Thallium is highly toxic and can be absorbed through the skin. Thus, it is always advisable to wear finger cots or gloves when handling any IR optical component.
Many overlook BK7 as a viable material for near-UV applications even though it can transmit down to about 300nm. Nonetheless, BK7’s transmission begins to dip around 340nm. There are some variables when it comes to the source of BK7, though it can be recommended for use above 350nm. When in doubt, sapphire and UV fused silica are the best options, they offer high transmission from UV to visible to NIR wavelengths.
When polarized light is incident on a conductive surface like a metallic coating, a 180° phase factor gets added to the beam. If you start with linear polarized light, this rotates the polarization direction from θ to θ +180° which is the same linear polarization direction. Circular polarization, which can be defined as two equal linear states with 90° phase difference between them, undergoes a more obvious change. 180° is added to the phase difference and it becomes 270° (or -90°). This means the linear state that was leading is now lagging the other (orthogonal) piece by a quarter wave.
Any visible pits and scratches will create light scatter which would be insignificant if there is plenty of light available but would decrease the signal in a low-light level application. An optic with a 20-10 scratch-dig, for example, will have better surface quality than an optic with 60-40. Provided the thicknesses are the same, glass transmission for uncoated fused silica is similar to the transmission for uncoated float glass in the visible range of the spectrum. UV Fused silica, however, does have much better transmission in the UV compared to float glass, if you would like a window with a higher surface quality rating.
Yes, we do have a stock lens solution for this. Cylinder Lenses placed one in front of the other, at the right distances, will invert the vertical dimension while maintaining the orientation of the horizontal. By taking two positive cylinder lenses and separating them by the sum of their focal distances, you will achieve a system that inverts the image without reversing it. The downside is that the resultant image isn’t very sharp which is what one would expect from what is basically a really inexpensive, one-dimensional Keplerian telescope.
Another, much simpler option is to use a Dove Prism. Dove prisms are used in binocular and telescopic systems to invert images in exactly the way mentioned. It's a simple, one-piece solution to your problem. It requires no focusing and is not as expensive as two cylinder lenses; but it is much bulkier than two cylinder lenses and would have to be placed very close one’s eye in order to work.
MgF2 has the solubility of approximately 0.0002g per 100g water at room temperature. So if the water is moving, it means that the MgF2 will be continuously dissolving at a very slow rate. After a long period of time, the whole layer of coating may be totally removed. In addition, the detergent solution will be alkaline [depending on the detergent used, pH value will vary from 7.5 (dishwasher) to 12 (commercial grade detergent)], there is a possibility that the MgF2 will react to form a salt which will appear as a white stain on the coating. In summary, MgF2 would not be ideal for long term use under water. Even if you use an uncoated window, there could be some staining from the glass reacting with the detergent.
Straight line accuracy is a measurement of the amount of error that a linear positioner will deviate from a perfectly straight line. Straight line accuracy is the error that is in the horizontal plane (x-axis), while flatness is the error in the vertical plane (z-axis). Both are measured at the center of the mounting surface and represent the maximum deviation for the overall length of travel. The straight line value is typically given as the worst case value for both errors.
When some bearings of a translation stage are supporting more of the load than other bearings, there is an uneven loading on the stage. These offset forces are referred to as pitch, roll, and yaw. Pitch has its axis of rotation perpendicular and in the same plane as the direction of travel. Roll has the axis of rotation parallel to the direction of travel. Yaw has rotation perpendicular to the plane of travel. See the accompanying illustration below:
Under most conditions, a laser beam cannot be seen traveling through the air. Since our eyes are essentially light collectors, we can only see light that enters the eye and is imaged onto our retina. When a laser beam encounters dust, mist, or smoke, some fraction of the light is scattered in the direction of the viewer's eyes and therefore becomes visible. Since these particles are rather small and will not stop the entire beam, all the tiny reflections make the beam look solid or continuous. This is why the beam appears to slowly fade as the dust (or scattering medium) dissipates. In the absence of any type of scattering medium, the beam will only be visible as a spot when it reaches its target and energy reflects back to the viewer. This principle can easily be demonstrated by using a flashlight on a dark night: if it is foggy, you can see the cone of light coming from the flashlight; if it is not foggy, you can only see the light as a spot at its target. If you see something that appears to contradict this concept, it is usually just 'movie magic'.
Pointing Accuracy, Bore Sighting, and Static Alignment all refer to how well the laser beam is aligned to the housing of the laser. All lasers inherently have an associated tolerance for alignment (pointing) accuracy. Pointing Accuracy is a measure of the angular difference between the propagating axis (where the laser light is pointing) and the mechanical axis (where the housing is pointing). The application typically requires the user to make sure that the mount has the adjustment to take some of those tolerances into consideration. Pointing Stability is how much the beam alignment changes over a period of time. These specifications are very important for aligning and positioning a laser.
There are many factors involved in sighting a beam at any given distance from the laser source: the output power of the laser is one concern. Low power lasers can be used for short distances, but higher power lasers are more widely used for long distances and for line and cross-line applications that require more energy. The wavelength of the laser is another important element. Detectors have a characteristic response that depends upon the wavelength of incident radiation. The human eye has a spectral response from 400 to 700nm with peak responsivity at about 550nm. A wavelength closer to the detector's responsivity peak appears brighter than a wavelength farther from the peak. For example, a 1mW laser at 633nm will appear brighter to an observer than a 1mW, 670nm laser. Even though both lasers have the same power and color (red), 633nm is closer to the human eye's 550nm spectral peak than 670nm. Beam divergence is also critical. As the energy spreads out into larger areas, the energy reflected back to the viewer from any one distinct point is reduced. Therefore, low beam divergence is an important technical concern for long distance applications. Ambient lighting will also determine the degree of visibility. High ambient levels at the target will yield low contrast and therefore low visibility. The best visibility generally occurs in subdued ambient light.
For more information on laser beam visibility, view Tackling Laser Beam Visibility.
M2 is a measurement of the quality of the beam propagation. It is a ratio of the actual beam propagation over the diffraction limit. It can be used to identify how the beam will change as it travels when compared to a Gaussian beam. The closer the value is to 1, the better the performance of the laser. An M2 value less than or equal to 1.2 is generally considered good performance. The value is useful in determining maximum focused spot sizes and the effects on beam delivery systems.
Spatial filters are used to "clean up" laser beams by filtering out unwanted multiple-order energy. The resulting beam intensity will still have a Gaussian profile. Spatial filters are particularly useful in interferometric and holographic applications. For a more in-depth discussion of what components make up a spatial filter system and how to use a spatial filter, view Understanding Spatial Filters.
When circularly polarized laser light passes through a Polarizing Cube Beamsplitter, P-polarized light is transmitted while S-polarized light reflected. On the other hand, when circularly polarized light passes through a Non-polarizing Cube Beamsplitter, the reflected and transmitted components contain the same polarization characteristics of the source beam. Namely, both the reflected and the transmitted components will be circularly polarized.
The output beam would be scattered according to the numerical aperture (NA). This in terms of angle of the fiber is equal to sin-1(NA) = θ. For example, if your numerical aperture is 0.22 then the angle at which the beam will exit the fiber is 12.7°. The only time this would not occur would be if macro-bending was not present and the fiber was perfectly straight. In this perfect, theoretical case, the beam will emerge collimated. However, in most cases, if there is even any movement off a straight axis, the output of the fiber will exit at a cone angle comparable to the NA.
Almost all lasers' excitation medium are either directly or secondarily electric. Gas lasers are excited via electric current and solid state by optical phenomena that are electrically controlled. This means that most standard lasers have a rise and fall time ultimately limited by electronics if you just consider traditional on and off. Using a low repetition q-switched or mode-locked laser with a pulse duration in the realm of your allowable fall time is best for this application. A femto-second laser might be nice if you can get your hands on one although most common types (Nd:YAG, Ti Sapphire, etc) have such high repetition rates that they might not work for your application. There are some low-repetition mode-locked, femto-second, fiber lasers that generally have fairly low repetition rates that would probably be ideal. Either way, an ultra-short pulse will be as close to instant-off as possible. Currently, we do not offer any lasers that match those criteria.
Understanding the entire application and the desired end results is an inherent key to a successful system. If a lens needs to be matched with a pre-selected camera, the sensor size and flange mount type specifications are needed. The basic system criteria that need to be defined to select the lens are the field of view, working distance, depth of field, and object resolution. Additional information about the system needs that will help select the actual type of lens are the size/weight, focusing capability, zoom capability, iris control, ability to accept a filter, accessories, and the cost.
For general component integration, these are the basic steps we suggest to follow: define your system parameters, match-up equivalent components, examine the illumination, and make any considerations for future modifications. There are fundamental parameters (such as field of view, working distance, etc.) used to define a system and these can be related to component specifications with a few calculations. The imaging system should create sufficient image quality to allow the desired information about the object to be extracted from the image. There are several factors that contribute to the overall image quality, such as resolution, contrast, depth of field, perspective errors, and geometric (distortion) errors. Our Electronic Imaging Resource Guide explain all these issues in detail, provide the necessary equations, and give case studies that go through each step of the process.
We have an Achromat Prototyping Assembly that can be used to create your own imaging system with any of our 12.5mm diameter achromatic lenses. A variety of f/#s are possible with the use of different selectable apertures. The lens cell accepts two achromats and threads directly into our Helicoid Barrel while retainers are used to fix the relative position of the cell. Coupled with our other C-Mount components, many variations can be created to fit your application needs.
Unfortunately, because the thin lens equation is only an approximation for theoretical lenses with no power and no physical thickness, it is not really appropriate for predicting Field of View and conjugate distances for complex lens assemblies. These assemblies involve real thick lenses that have both thickness and power, as well as, greater field angles. Therefore, these types of calculations are usually limited to lens design software such as ZEMAX or Code V. If you are looking for something to do this you might want to look into software such as OSLO which can be found online and is a free download.
Nonetheless, there a few equations that you may find useful for calculating field of view and working distance. The equations are as follows: Tan(Angular Field of View/2)=Object Size/(2 x Working Distance) or Focal Length = Image Size x (Working Distance/Object Size) These equations are very useful for estimation. For more accurate results, most designers use optical design software such as ZEMAX or Code V.
An in-line video system introduces illumination into the imaging lens before the objective and aligns it with the optical axis. The "in-line" name actually refers to the type of illumination and is also known by other names such as axial, co-axial, through-the-objective, vertical, and incident brightfield. The clear difference from other types of illumination is that in this case the light is transmitted through the objective. As an example, we offer an InfiniTube In-Line Assembly that uses infinity-corrected objectives. The image from this type of objective is collimated (parallel) light prior to being focused by a secondary lens assembly onto the sensor plane. Since the light between the objective and secondary lens is collimated, the separation between the lenses can be adjusted to accept a beamsplitter that will introduce horizontally aligned input light and redirect it vertically down to the objective. This type of illumination is very efficient for high power objectives that need to evenly illuminate an opaque object, such as a semiconductor wafer. Since this type of system is very sensitive to mounting with objective powers 20X and higher, we recommend using a vibration isolation table (not available from Edmund Optics). For proper focusing, a rack and pinion movement is always suggested for the system.
If a pattern (such as a crosshair) is needed to be placed over the image in a digital system, the combination of an image capture board and image analysis software can be used. If the same effect is needed for an analog system, a video micrometer is typically used. It is a device capable of laying controlled lines or patterns on an analog video output signal that is transmitted to a video printer or monitor. The only other way to place crosshairs, guidelines, or complex patterns on the image is to use a glass reticle placed in the video lens or microscope. Since most video lenses do not have this ability, using an electronic device is a viable alternative solution. For microscopes, an eyepiece that can accept a reticle is used and a relay lens is then used to connect the scope to the camera. Since different video micrometers have different functions, care must be taken to select the model that has the necessary capabilities.
There are a few ways to measure Modulation Transfer Function (MTF), but it is very difficult to do so with any precision on a flat (plano) optic such as a window or filter. Measurements for MTF are generally done on systems by imaging a target of known contrast and known size at a known magnification and measuring the resultant contrast and size. In practice, this can be done by imaging a point, a bar target, a sinusoidal target, or any random target. There are many ways to test MTF but the reason none are appropriate for windows or filters is because they are all measurements of an image, whereas, windows and filters don't form images. One could determine the MTF of a window or filter by testing an optical system to use as a baseline, then inserting the window or filter into the optical path and re-measuring. The MTF of the window would then be the second result divided by the baseline result. The problem with doing this is that the MTF of the window or filter would almost certainly be within the uncertainty of the measurement. Even low quality windows and filters have very good MTF. Because MTF isn't very telling for windows or filters, their ability to transmit an image is usually given in terms of transmitted wavefront distortion. Rather than the error in contrast as measured in MTF, transmitted wavefront distortion measures the displacement of a theoretically perfect wavefront as it passes through an optic. Measuring this requires an interferometer or similar device. For example, a Schlieren System would help to visualize slight wavefront variations, but couldn't help measure them easily. Whatever test one does on a window or filter, there is very little chance that it could have an appreciable effect on any camera-based system's image.
In this particular case, your problem isn’t vignetting, it is in fact one of resolution. If you had the necessary resolution, then you would not need to insert an aperture to improve contrast. The reason you gain contrast by inserting the aperture is because you are vignetting. Vignetting often improves contrast in lower-end imaging systems by eliminating the hardest to control rays i.e. the ones at the edges. So for you, vignetting is good. The main thing you could do to improve your setup is use a better lens. Instead of a Double Convex (DCX) Lens, perhaps use an Achromatic Lens of similar diameter and focal length. An achromatic lens would really improve the resolution in your setup, especially in a polychromatic application.
Another option you could try is to reduce your field of view. If you don’t need such a large field of view, then try to utilize the smallest but still most adequate for your setup. In this case, a DCX lens could work just fine.
Proper alignment of an optical system can be complicated. It usually isn’t as simple as pointing a laser at something and aligning all the optics so that the laser beam stays straight. While this approach occasionally works, the introduction of the first optic will usually cause the beam to diverge to the point where it’s impossible to determine if it is still traveling in the correct direction. Assuming the spot doesn’t become too large when an optic is introduced, you can add each individual element and center the spot on the original spot. This gives you a rough alignment that may or may not be good enough for your purpose, but certainly cannot be quantified.
The best way to align optical components to one another is to position each individual element so that the optical axis remains fixed. This is called active alignment. Generally, this is done by using a fixed, collimated source (like a laser) and a detector that can only move along the optical axis. The first element is introduced and positioned such that the image it forms is coaxial to the original optical axis. The next element is introduced and the process is repeated. The main difficulty comes from the fact that each optical element introduced will form an image at a different location or not at all. This requires a detector that is both mobile along the optical axis and focusable. The equipment required for this is specialized and expensive. Since each optical component has both a physical centerline and an optical centerline (the optical axis). These are generally quite close and for most applications alignment of physical centerlines is good enough. Of course, this is easier said than done. To align the centerlines of two components requires fine adjustment to position in both the X and Y axes and rotation in both the X and Y axes. If all components have the exact same diameter, a V groove will align the physical axes. For components that do not have the same diameter, mechanics that center the optics within them and have a standardized outer diameter are helpful.
Our C-Mount Components and T-Mount Components are a good example. Mounting elements in these and connecting the components to one another aligns the physical centerlines to a high degree - and they even integrate with microscopes. This is especially easy to integrate with a camera as the mounting flange of the camera can mate to our C-mount and T-mount components either directly or through the use of an adapter making the sensor centered on and orthogonal to the optical axis which is ideal. If you do not have access to a detector which can move only along the optical axis and is focusable, or for some reason our C-mount and T-mount components or some other physical retention system is not acceptable for your system, there are other options.
The easiest to use and most common of these would be to use an autocollimator to angularly align all components. Since autocollimators can only make measurements off flat surfaces, the use of additional items with known properties may be necessary to use as references. For instance, in the set up described above, you could align the sensor of the camera to the autocollimator. Let’s say the next optic is a PCX lens with the convex side facing the collimator. The collimator can’t take a reading off the convex side. In order to determine if the plano side is parallel to the camera’s sensor, you would need to physically contact it with a flat reflective surface and allow it to project past the edge of the lens. You could then take measurements with the autocollimator off of the protruding surface and infer the position of the plano side of the lens. Once angularly aligned, proper translational positioning in X and Y can be determined experimentally.
Generally speaking, the use of a Holographic Diffuser, Condenser Lens, and Plano-Convex (PCX) Lens would satisfy the application. The holographic diffuser (elliptical in this case) would take the filament and image it as an approximate circular blur at a particular distance from the diffuser (based on diffusing angle chosen). By placing a filament 1 focal length from the condenser lens, the resulting output will be approximately collimated. Short focal length lenses tend to work best for this type of application. The PCX lens would then be used to refocus the light a given distance (EFL of the PCX Lens) from the lens. The distance of the PCX lens from the condenser lens is arbitrary. You can pick and choose relative to the application.
For example, you could use a Condenser lens (EFL = 13mm) and PCX Lens (EFL = 100mm). Place the condenser lens 13mm from the filament, and place the diffuser between the filament and condenser lens. The spacing between the condenser and PCX lenses can be 87mm (arbitrary). Overall, the resulting filament to final focal position is 200mm. Using geometry and trigonometry, you can determine exactly where the PCX lens needs to be placed in order to produce a 20mm spot at a distance of 200mm from the filament.
The system you are trying to model is basically a Koehler Illumination setup. We have a great EO Tech Tool – Koehler Illumination - that helps you choose the best lens parameters from a few simple variables.
In a bundle of fibers, if the relative position of each individual fiber at one end of the bundle is exactly the same as those at the other end, then the fibers are said to be coherent. Coherent fiber bundles such as those in our Fiber Optic Tapers are used to relay an image from one end of the fiber to the other, whereas incoherent fiber bundles cannot. Incoherent fibers are primarily used to transmit light or signals rather than images.
Illuminators have a certain color temperature, which only slightly affects the spectral contrast of an image. When an illuminator is used with color filters, different spectral contrasts can be obtained. Color camera settings (Red/Blue gain level and AWC) in conjunction with lamp selection (quartz-halogen, metal halide and fluorescent) can yield further optimization. Edmund Optics® carries a variety of color filters for our illuminators and light guides.
The typical color temperature of a typical quartz halogen lamp and bulb such as our 150W EKE Replacement Bulb is 3250 Kelvin, while that of a typical metal halide lamp and bulb such as our 100W Metal Halide Replacement Bulb is 5300 Kelvin. Spectral curves are available by visiting the presentation for each replacement bulb.
"Ripple" is a sinusoidal fluctuation of light intensity. This can cause a problem with machine vision systems that utilize computer algorithms, when constant contrast is required for proper data acquisition. The AC current powering the illumination source causes this ripple in illumination systems. Illumination sources can be DC regulated, which nearly eliminates this ripple effect. Our Dolan-Jenner DC-950H Regulated Fiber Optic Illuminator offers = 0.4% ripple.
A Schlieren test is an optical system that detects changes within a test area medium (air) and records the changes in the form of an image on a screen. The image is formed by refraction and scattering from what is introduced into the test area, which are areas of varying refractive index. A source directs light onto a spherical mirror, which collimates the light and redirects it onto a second identical mirror. The light is then focused onto an included screen. The space between the mirrors is the test area, where the small particles introduced are made visible by the light source and seen as shadows on the screen. Brightness variations on the screen will occur according to changes within the test area. Spherical mirrors are used due to the slight off-axis nature of the set-up. Applications include the determination of refractive index, fluid and air current flow, and flame analysis. Film or video cameras can also be added to the system in place of the imaging screen. Two systems are available with different size F10 mirrors in order to select the test area size that best matches the application.
Unfortunately, the reticles mounted in our alignment telescopes (such as our Precision Universal Telescope, and our Close Focus Multi-Purpose Telescope) cannot be removed. The reticles are permanently placed in a calibrated location that is in the optical path of the telescope.
Proper alignment of an optical system can be complicated. It usually isn’t as simple as pointing a laser at something and aligning all the optics so that the laser beam stays straight. While this approach occasionally works, the introduction of the first optic will usually cause the beam to diverge to the point where it’s impossible to determine if it is still traveling in the correct direction. Assuming the spot doesn’t become too large when an optic is introduced, you can add each individual element and center the spot on the original spot. This gives you a rough alignment that may or may not be good enough for your purpose, but certainly cannot be quantified.
The best way to align optical components to one another is to position each individual element so that the optical axis remains fixed. This is called active alignment. Generally, this is done by using a fixed, collimated source (like a laser) and a detector that can only move along the optical axis. The first element is introduced and positioned such that the image it forms is coaxial to the original optical axis. The next element is introduced and the process is repeated. The main difficulty comes from the fact that each optical element introduced will form an image at a different location or not at all. This requires a detector that is both mobile along the optical axis and focusable. The equipment required for this is specialized and expensive. Since each optical component has both a physical centerline and an optical centerline (the optical axis). These are generally quite close and for most applications alignment of physical centerlines is good enough. Of course, this is easier said than done. To align the centerlines of two components requires fine adjustment to position in both the X and Y axes and rotation in both the X and Y axes. If all components have the exact same diameter, a V groove will align the physical axes. For components that do not have the same diameter, mechanics that center the optics within them and have a standardized outer diameter are helpful.
Our C-Mount Components and T-Mount Components are a good example. Mounting elements in these and connecting the components to one another aligns the physical centerlines to a high degree - and they even integrate with microscopes. This is especially easy to integrate with a camera as the mounting flange of the camera can mate to our C-mount and T-mount components either directly or through the use of an adapter making the sensor centered on and orthogonal to the optical axis which is ideal. If you do not have access to a detector which can move only along the optical axis and is focusable, or for some reason our C-mount and T-mount components or some other physical retention system is not acceptable for your system, there are other options.
The easiest to use and most common of these would be to use an autocollimator to angularly align all components. Since autocollimators can only make measurements off flat surfaces, the use of additional items with known properties may be necessary to use as references. For instance, in the set up described above, you could align the sensor of the camera to the autocollimator. Let’s say the next optic is a PCX lens with the convex side facing the collimator. The collimator can’t take a reading off the convex side. In order to determine if the plano side is parallel to the camera’s sensor, you would need to physically contact it with a flat reflective surface and allow it to project past the edge of the lens. You could then take measurements with the autocollimator off of the protruding surface and infer the position of the plano side of the lens. Once angularly aligned, proper translational positioning in X and Y can be determined experimentally.
Optics Application Examples – Read our most popular Optics app note. Learn about detector systems, selecting the right lens, and building a projection system.
Laser Spot Size Calculator – Use our featured EO Tech Tool to determine spot size from user-supplied working distances.
Spotlight on EO – What's new in the tech library? With new content every month, check back often for the latest updates.
