Questions Techniques Fréquemment Posées

For a detailed description of dispersion and GVD, please read our Dispersion application note.

Not yet - optical components are some of the highest precision products manufactured today with surface accuracies of tens of nanometers, surface roughness values in the tens of angstroms range, and very high levels of internal (index of refraction) homogeneity being common. Current 3D printing and additive manufacturing techniques yield parts with specification tolerances that are many orders of magnitude larger than what traditional manufacturing methods can deliver. Other than select illumination or beam shaping applications, 3D printing is not going to produce precision optics within the near future.

A full list of EO’s manufacturing tolerances can be found on our Aspheric Manufacturing Capabilities page.

EUV photons have an energy of around 90eV; the typical ionization energies of organic materials and metals are 7-9eV and 4-5eV respectively. Consequently, EUV photons are easily absorbed, generating photoelectrons and secondary electrons which prevents EUV radiation from transmitting through virtually all materials.

Edmund Optics^® can manufacture optical components with complex geometries out of optical glass, ZERODUR^®, Ceramics, Corundum, Tungsten Carbide, and even composite materials.

The maximum component diameter that Edmund Optics^® can manufacture using our DMG MORI^® ULTRASONIC 5-Axis Precision Machine Centers is 175mm.

The high upfront cost of CNC equipment prevents it from being adopted universally, but its numerous advantages and long-term cost savings are making these machines become more universally used.

Yes, Edmund Optics® has a staff of experienced optical and mechanical designers, along with world class manufacturing, to support prototypes and deliver the lens you require for your application. For more information, please contact our Technical Support Engineers.

While we do not sell CGHs for measuring aspheric lens surfaces, we do sell CGHs for measuring cylindrical optics made by Arizona Optical Metrology (AOM). Lean more and buy now here.

A CGH has a minimum feature size in its interference pattern that limits the maximum possible diffraction angle. This is why an aspheric CGH is often used along with a reference sphere in the interferometer to reduce the required diffraction angles.

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.

Lenses

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.

Mirrors

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

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.

Gratings and Wire-Grid Polarizers

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.

Holographic Diffusers

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.

Laser pulses with picosecond, femtosecond, and attosecond pulse durations (<100ps) are typically considered to be “ultrafast.”

CRDS can only be used to measure mirrors with a reflectivity above 99.5% because lower reflectivities result in ring down times that are too fast for the system to detect. The best technique to determine reflectivity depends on the reflectivity level and application requirements.

Continuous wave (CW) 2µm lasers create heat-affected zones at the top and bottom surfaces during laser materials processing, which reduces the precision of the process. On the other hand, pulsed 2µm lasers create smaller heat-affected zones, leading to less surface damage and more precise processes.

Radiation from 1µm lasers has much lower absorption than 2µm lasers and penetrates deeper into tissue, resulting in larger areas of injury and more unnecessary dead tissue. Because surgery is a very precise process, the depth of cuts need to be finely controlled in order to reduce damage to the underlying tissue. 2µm lasers offer this precision and should be considered for these surgical applications.

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.

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.

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.

Edmund Optics does carry lasers that can be used to mark or cut select materials. The minimum power typically used with one of these lasers to cut or mark is more than ten Watts of power. At these kinds of output powers, safety is a major factor and must be taken into consideration.

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'.

An in-line microscope introduces illumination into the system 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. An infinity-corrected system is used for this type of microscope. Since the light between the objective and secondary lens is collimated, the separation between these 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 platform. For proper focusing, a rack and pinion movement is always suggested for the system.

Microscope objectives come in many different designs. Three of the most common are achromatic, semi-plan and plan. In an achromatic objective, which is the most common type, there is one achromatic lens. Achromatic objectives correct for color and have a flat field in about the center 65% of the image. This is not to say that the outer 35% of the image will be blurry- this just means that if there are aberrations, they occur in the outer 35% of the image. A semi-plan, or semi-planar objective, is an intermediate between the achromatic and the plan objective. Semi-plan (sometimes called micro-plan as well) objectives have an 80% flat field. A plan (or planar) objective corrects better for color and spherical aberration than either the semi-plan or the achromatic objective. Plan objectives have a flat field about the center 95% of the image. While plan objectives give you flatter fields than achromatic objectives, they also have a higher price.

What is the difference between Huygenian, Wide Field, and Periplan eyepieces?

Eyepieces for both microscopes and telescopes come in varying optical designs. The major differences between the three microscope eyepiece designs we carry is listed below:

• Huygenian eyepieces consist of two plano-convex lenses placed with both convex faces towards the object. Designed for use with low power achromatic microscope objectives, Huygenian eyepieces tend to have an average eye-relief and are very economical.
• Wide Field microscope eyepieces consist of one achromatic doublet and one plano-convex lens with the convex side facing the doublet. Ideal for high power achromatic microscope objectives, wide field eyepieces have a long eye relief and are moderately priced.
• Periplan eyepieces consist of three lenses: one achromatic doublet and two plano-convex lenses with the convex lenses facing each other just below the doublet. Best used with plan and semi-plan microscope objectives, periplan eyepieces have an average eye relief and tend to be more expensive than either huygenian or wide-field eyepieces.

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.

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.

Depth of field describes the difference between the closest and furthest distances at which an object will maintain a certain level of resolution without refocusing, whereas depth of focus describes the different sensor positions through which focus can be maintained with a stationary object.

The TECHSPEC^® CA Series Fixed Focal Length Lenses feature a TFL Mount and have been designed specifically for new large sensor formats.

The TECHSPEC^® LH Series Fixed Focal Length Lenses feature a lens option with TFL-II Mounts and have been designed specifically for new large sensor formats.

Edmund Optics^® offers Liquid Lens Telecentric Lenses with Primary Magnifications (PMAG) of 0.15X, 0.24X, 0.37X, and 0.75X. You can find more information on the product family page.

Yes, we can make customized Liquid Lens Telecentric Lenses tailored to your specific application. For more information, please contact our application support engineers.

Yes, we can integrate liquid lenses into other types of lenses as a custom request. We also offer the modular Cx Series Fixed Focal Length Lenses, in which you can integrate interchangeable accessories including liquid lenses, fixed apertures, and internal filter holders.

Liquid lenses change focus to different working distances in a matter of miliseconds.

You can find more information on Stability and Industrial Ruggedization in our Ruggedization of Imaging Lenses application note and whitepaper in the Resources section at the bottom of this page.

Yes, we can ruggedize the lens and also do a number of other modifications such housing modification, working distance adjustment, filter or liquid lens integration, aperture replacement, and more. For more information, please contact our Technical Support Engineers.

Yes, please submit a prescription request and one of our Technical Support Engineers will contact you.

Ingress Protection Ruggedization is another type of ruggedization in which lenses are sealed using O-rings or RTV silicone to make them waterproof, dustproof, and fog proof. EO offers an off-the-shelf line of Ingress Protection Ruggedized lenses, TECHSPEC^® HEO Series M12 μ-Video™ Imaging Lenses. For more information on Ingress Protection Ruggedization, please visit our Ruggedization of Imaging Lenses application note.

The best lens mount for an imaging system is dependent on the application requirements, the use environment, and any other predefined limitations.

Each lens mount provides a certain set of benefits and disadvantages over others.

• For stability and to resist performance loss due to shock and vibration, always try to use a threaded type mount (e.g. C-Mount, S-Mount, or TFL-Mount) over a non-threaded mount type (e.g. bayonet).
• For maximized use of the full size of the image sensor, pair the machine vision camera to an imaging lens with an appropriately sized mount. This ensures that as little of the image circle is wasted as possible, that the image is not clipped at corners, and that the optical components used in the imaging lens have been optimized over the full field of the sensor, ultimately optimizing the cost-to-performance ratio. For more information on sensor sizes, see Sensors.
• S-Mount: Up to 1/2”
• C-Mount: ½” to 4/3”
• TFL-Mount: 4/3” to APS-C
• TFL-II or F-Mount: APS-C up to full frame (35mm)
• For sensors greater than full frame, custom or non-standard mount types may be required.
• Certain machine vision cameras require the use of lenses with specific back flange distances. The most common back flange distance in machine vision is approximately 17.5mm and is the back flange distance associated with the C-Mount, TFL-Mount, and TFL-II Mount. A notable exception is the CS-Mount which is identical to the C-Mount but is used with cameras that require approximately a 12.5mm flange distance. Another exception is the F-Mount requires a back flange distance of 46.5mm.

For more information on imaging lens mount types, read about Lens Mounts.

M12 or micro-video imaging lenses are typically board lenses that are small and feature an S-Mount type camera or lens mount. The S-Mount is a standard lens mount used in machine vision and M12 refers to the metric thread type with a nominal diameter of 12mm, a pitch of 0.5mm (M12 x 0.5), and without a standardized flange distance (see The Anatomy of a Lens) as many other mount type have including the C-Mount and TFL-Mount for example. These lenses are often ideal for space- and weight-constrained applications including OEM implementation, CCTV, and other board-level cameras. Additionally, M12 lenses are low cost alternatives to standard-sized fixed focal length lenses. For more information on imaging lenses and their differences, read Types of Machine Vision Lenses.

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.

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.

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.

Primary magnification (PMAG) is the magnification of the lens alone. It is the ratio between the camera's sensor size and the field of view; put simply, it is the "work" done by the lens. System magnification is the total magnification from the object to the image on the monitor; this is the "work" done by the entire system. It is the product of the PMAG and the camera-to-monitor magnification (the ratio between the monitor size and the sensor size). Edmund Optics typically uses horizontal values for the sensor-to-field of view ratio and diagonal values for the monitor-to-sensor ratio.

Yes, these machine vision cameras feature new APS-C or APS-H sensor formats.

Yes, Edmund Optics has partnered with LUCID Vision Labs to offer the ATLAS^™ camera family.

There are many factors that contribute to an application setup’s resolution capability. However, in terms of monochrome versus color, because of bayer pattern de-mosaicing, color sensors tend to lose a small amount of resolution compared to their equivalent monochrome counterparts.

What you are describing is a common issue people have when removing IR cut filters from cameras to do IR photography. Mainly, it is assumed that since the filter itself seems to have no optical power then removing it will have no effect on focus. This is not the case because even though the filter is has no optical power, it still changes the optical path length by refracting incident light. This in turn changes the point of focus. The problem can be easily corrected by simply replacing the filter with a clear piece of glass that is transmissive in the NIR such as BK7 or Fused Silica. It is important that this piece of glass be roughly the same thickness and index of refraction as the filter glass to simulate its optical effects without taking away from the IR performance of the camera.

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.

"Progressive scan" means that the charge on the CCD (charge coupled device) accumulates simultaneously and is outputted sequentially (line by line) as opposed to the outputting of every other line (odd field/even field readout) that occurs more commonly in interlaced scanning CCDs. The non-interlaced image of a progressive scan CCD contains the full vertical and horizontal resolution of the object. Progressive scan cameras are used when capturing images of events that happen very quickly, i.e., in high-speed inspection applications. If you are not trying to capture a high-speed event, you do not need a progressive scan camera, although you might want to plan ahead for future applications.

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.

Test targets can be used to evaluate or calibrate an imaging system's performance. The correct assessment of an imaging system is used in certifying proper measurements, establishing a baseline between systems working in parallel, or for troubleshooting. Edmund Industrial Optics offers patterns that can characterize image quality in terms of its components: resolution, contrast, depth of field, and distortion. Each target has its own unique design that defines its application. Several targets can also be applied to test for other image quality characteristics. For a definition of the image quality terms and recommended targets, view Choosing the Correct Test Target.