Questions Techniques Fréquemment Posées

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.

Substrate Comparison Chart

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.

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.

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.

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.

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.

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.

Laser Diode Modules 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.

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.

For low-end laser devices where the beam quality and divergence angle are not as important, you can often get away with a single aspherical lens. But whenever circularization, divergence, and confocality are essential, cross cylinders are generally the most cost-effective option.

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.

Strictly speaking, there are optical designs which enable fiber coupling without first collimating the output of the diode laser, but all of these designs suffer from massive astigmatism which can significantly reduce the efficacy of the fiber coupling. Having a collimated beam inside of the laser package allows for the addition of optical elements such as micro-optical isolators and bandpass filters.

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.

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

Use of compressed air, reagent-grade alcohol, or de-ionized water and standard lens cleaning methods are recommended. Do not use acetone as it will damage the lens and epoxy.

The low AOI of ultrafast highly-dispersive mirrors allow for reflections between multiple mirrors, so several mirrors will be used at once for maximum dispersion compensation and pulse compression.

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.

Some of the most common materials for use in the 2µm spectral region are fused silica, zinc selenide, calcium fluoride (CaF₂), germanium, and sapphire. More information about compatible optical materials and their properties can be found at our Characteristics of 2µm Lasers application note.

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:

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.

We offer a C-Mount Light Guide Adapter that will hold a fiber optic light guide on one side by using its corresponding light guide adapter (this stainless steel bushing is not included and is selected based on the light guide's ferrule diameter). The other side has a standard C-Thread for integration with our extensive line of C-Mount components. By using one of our C-mounted Cube Beamsplitters, an in-line system can be assembled. Additional optics can also be inserted prior to the beamsplitter in order to create a collimated light beam from the light guide.

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'.

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.

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.

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.

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.

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.

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.

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.

Strictly speaking, there are optical designs which enable fiber coupling without first collimating the output of the diode laser, but all of these designs suffer from massive astigmatism which can significantly reduce the efficacy of the fiber coupling. Having a collimated beam inside of the laser package allows for the addition of optical elements such as micro-optical isolators and bandpass filters.

Yes, short ultrafast pulses interact with optical coatings and substrates in a way that is different from other laser pulses, leading to different damage mechanisms. For more information, please read our LIDT for Ultrafast Lasers application note.

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.

Some of the most common materials for use in the 2µm spectral region are fused silica, zinc selenide, calcium fluoride (CaF₂), germanium, and sapphire. More information about compatible optical materials and their properties can be found at our Characteristics of 2µm Lasers application note.

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.

Both DIN (Deutsches Institut für Normung) and JIS (Japanese Industrial Standards) are industry standards for microscope objectives and eyepieces.

When referring to microscopes, a DIN standard eyepiece or objective uses a basic 160mm tube length. DIN microscopes begin with an object-to-image distance of 195mm, then fix the object distance at 45mm. The remaining 150mm distance to the eyepiece field lens sets the internal real image position, which is defined as 10mm from the end of the mechanical tube (which gives the 160mm tube length). DIN standard eyepieces have an international standard 23mm diameter. DIN standard objectives often times have "DIN" etched on the side and have a standard 0.7965" diameter thread, 36 TPI, 55° Whitworth threading.

A JIS standard system has a 170mm tube length. JIS standard eyepieces also have an international standard 23mm diameter, however JIS standard fixed the object distance at 30mm. JIS standard objectives also have a standard 0.7965" diameter thread, 36 TPI, 55° Whitworth threading.

Most microscopes are DIN standard. DIN and JIS standards are interchangeable from a mechanical point-of-view. Please note, however, that the magnification of a microscope is calculated by multiplying the objective and eyepiece power together. This is assuming you have the same standard microscope, eyepiece and objective. If your eyepiece, objective, or tube length does not conform to the same standard, then recalculation of the total magnification is necessary. Also note that non-standardized microscopes exist, so be careful when choosing an eyepiece or objective.

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.

There are multiple ways to achieve the effect you require; however, the most straightforward is utilizing Darkfield Illumination. Darkfield Illumination is ideal for imaging transparent or translucent objects. Light from the Darkfield illuminator, usually a special type of ring light guide, enters the object through the edge, rather than from above, enabling one to see the object’s profile. View Choosing the Correct Illumination for additional information on pros and cons of various illumination setups.

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.

A telecentric lens is a video imaging lens that optically corrects for perspective errors due to parallax. Telecentric lenses yield constant magnification over a range of working distances, virtually eliminating viewing angle error. Objects in the field of view of a telecentric lens maintain their perceived size no matter where they are located. These lenses are widely used in machine vision systems that require accurate measurements of three-dimensional objects with slight height variations. By eliminating the perspective errors and magnification errors inherent in conventional lenses, telecentric lenses yield dimensionally accurate images that are easily interpreted by software. For a more detailed look at telecentric lenses, view The Advantages of Telecentricity.

Since we have not tested the other two lubricants that you mentioned (mineral oil and lithium grease) on our VZM™ Imaging Lenses we cannot say what they will do. We use a combination of brass and metal material to hold the optics, so there should not be a major problem with using either of those two lubricants. However, there is still the possibility of corrosion or deposition.

To be safe, using the lubricant originally used on the VZM™ lenses - NYE NYOGEL 779 - would be the best option. We recently looked inside the lens tube of one of our VZM™ lenses and could not see any issues with corrosion on the internal workings.

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.

"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.

Edmund Optics offers a series of TECHSPEC® Double Gauss Imaging Lenses optimized for electronic imaging applications that use high-resolution cameras. They use a modified basic double gauss lens design in order to create a high-performance multi-element lens that will exceed the performance of typically available fixed focal length lenses. The symmetrical design corrects for many optical aberrations, including a distortion that is kept below 0.3%. Conventional lenses often use the same designs that were originally used for photographic objectives. A typical ½" CCD high-resolution monochrome camera (like the Sony XC-75) has a cut-off resolution of 55 lp/mm. Even when focused at infinity, our Double Gauss lenses will have a better resolution than the camera. Their expanded performance yields image resolution greater than 100 lp/mm. After inspecting the MTF curves for 50mm lenses at f/4 and a 400mm working distance, our Double Gauss lens has a much higher contrast (70%) than a typical fixed focal length lens (35%) at 55 lp/mm.

Our TECHSPEC® Double Gauss Imaging Lenses provide high-performance, support large sensor formats, have low-profile compact housings, and an exceptional value. We offer two series of these lenses, Fixed Focus and Focusable. Focusable versions have set screws to lock both manual iris and focus rings in place. Lens Prescription Data is available for qualified optical designers.

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.

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.

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.

When exposure time and frame rate are set, and you decrease the AOI (Area of Interest), our EO USB2.0 cameras try to maintain the same bandwidth that was originally preset. This results in frame rate increasing, or if it is already at its maximum, exposure time decreasing. However, you can easily reset any of these settings. Also, you can use the included software to fix two of the three settings if you do not want them to change.

The power requirements that you outlined tip the scales in favor of FireWire. USB can only deliver 2W of power but Firewire Cameras, specifically FireWire.b cameras, can deliver a maximum of 25W. Though FireWire.b cables are actually rated to withstand 45W, using the lower value is recommended for safety reasons.

There are probably two issues at play that are cause the problem. First, make sure there is enough bandwidth for the amount of data to transfer. If this is insufficient, then the cameras won’t be able to acquire and transfer their data over the network. Second, it is known that GigE Cameras do not work the same with all network cards; it is best to use the recommended one though the manual does not require it.

Yes, you do need a frame grabber that is compatible with both your computer and digital camera. Even though the camera outputs digital data, the available computer ports (RS-232 for example) do not have the bandwidth or even the right connectors to be able to be used with a digital camera.

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.

"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.

"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.

Since infinity corrected objectives, like the Mitutoyo objectives, are designed to form images at infinity - when using them with a camera, a tube lens is needed to form the image onto a sensor. Most Mitutoyo products have M26 threads or no threads at all, unfortunately, making them difficult to use with most C-mount (1"" x 32TIP) cameras. On the bright side, Edmund Optics® has Accessory Spacer Tubes and Adapters and C-Mount Extension Tubes to make this process as simple as possible.

#54-428 MT-4 Accessory Tube Lens:

Use #56-992 Mitutoyo to C-mount Camera 152.5mm Extension Tube to connect the MT-4 Tube Lens to a C-mount camera. This extension tube is M26 on one side to attach to the tubes lens and C-thread on the other to attach to a C-mount camera. The MT-4 Tube Lens attaches directly to a Mitutoyo objective.

#54-774 MT-1 OR #56-863 MT-2 Accessory Tube Lenses:

This one is a little tricky. #58-329 Mitutoyo MT-1/ MT-2 C-mount Adapter can be opened up and the MT-1 or MT-2 Tube Lenses fit inside. Since the tube lenses themselves have no threads, this adapter provides the necessary C-threads on both sides. Between this adapter and the C-mount camera, you will need an additional 190mm of extension tubes. Since the tube lens does not attach directly to the objective, #55-743 Mitutoyo to C-Mount 10mm Adapter needs to be attached to the Mitutoyo objective (this adapter adds 10mm of length and adapts the M26 thread to a C-thread). An additional 76.5mm of space between the tube lens and the objective is optimal, but really you only have about 56.5mm of space between #55-743 and #58-329 since each adapter adds about 10mm of space. With this 56.5mm of space, you can use extension tubes or add other items such as beamsplitters, filters, polarizers, etc (this is the benefit of using the MT-1 and MT-2 tube lenses.

Please note that 76.5mm is the recommended distance since these objectives are infinity corrected. However if the distance is too short, you risk vignetting, and if the distance is too long, the resultant image will be dim because of insufficient light. So, from the top – it is a C-mount camera, 190mm of extension tube, MT-1 or MT-2 Accessory Tube Lens inside #58-329 Adapter, 56.5mm of extension tubes, #55-743 adapter, and then the Mitutoyo objective.

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.

Fiber optic light guides transmit light based on the principle of total internal reflection. Light incident on cylindrical fibers of either acrylic or glass materials can be transmitted through these fibers with little attenuation.

Useful for applications with very tight space or limited access constraints, Fiber Optic Illumination can provide a wide range of useful illumination geometries from spot lights and ring lights to diffuse sources and line lights. Light guide optics are also able to brave certain environments where using electronics would otherwise be a danger. Fiber optic illumination can also be intensity controlled and very easily aimed towards objects. Broadband illuminator sources provide white light illumination, which is composed of all of the colors of the visible spectrum.

We offer a C-Mount Light Guide Adapter that will hold a fiber optic light guide on one side by using its corresponding light guide adapter (this stainless steel bushing is not included and is selected based on the light guide's ferrule diameter). The other side has a standard C-Thread for integration with our extensive line of C-Mount components. By using one of our C-mounted Cube Beamsplitters, an in-line system can be assembled. Additional optics can also be inserted prior to the beamsplitter in order to create a collimated light beam from the light guide.

Unlike ordinary incandescent bulbs, LEDs do not have a filament that burn out. LEDs emit light when electricity runs through a semiconductor material, which, in turn, excites electrons.

Compact, energy efficient, and economical, LED illumination is a great choice for both industrial and laboratory applications. Available in different configurations, such as ring lights, backlights, domelights, or arranged in custom configurations, LEDs can be easily integrated into virtually any illumination task. A main advantage of LED illumination is the freedom to easily select white, IR, RGB, or specific wavelength outputs in a variety of different geometries. An RGB output is recommended for applications that require user adjusted color balance, while Red and IR LEDs are a great choice for monochromatic applications. LEDs are also able to be strobed and/or overdriven, which can often be an invaluable function for high speed imaging applications on assembly lines. Intensity control is also possible with certain intensity controllers and power supplies. Very long lifetimes with predictable intensity fall-off are further benefits of using LED illumination sources.

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.

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.

High frequency illumination provides a flicker and ripple free output that assures image quality by maintaining constant frame to frame gray level. Fluorescent lights are the best example of high frequency illumination. When determining the correct illumination for one's camera setup, make sure the frequency of the illumination is higher than the frame rate of the camera. This will help to insure constant illumination and therefore the best image quality from frame to frame. Correspondingly, high frequency illumination helps reduce operator fatigue and eye strain when used over long durations.

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.

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.

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.

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.

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.

It seems like you are experiencing some temporally-localized interference. If you look at a short enough slice of time, the photodiode might pick up the constantly shifting course of constructive and destructive interference that is basically what its called speckle.

Laser Diode Modules have a fair amount of noise if you look on a very short time scale. The total noise is a combination from multiple sources including but not limited to power supply noise, mode hopping, thermal effects, and optical feedback. These noise sources can be severely reduced by using a low-noise power supply and a heat sink or preferably a Thermo-electrically cooled (TEC) laser. In order for a laser to have a perfectly consistent output even on that small of a time scale, the necessary controls need to be designed in from the ground up, which is generally not the case with laser diode modules.

Silicon detectors are typically used for detecting laser signals and converting the signal to a voltage differential. For an in-depth explanation on the use of our silicon detectors, as well as circuit diagram examples, view Basic Principles of Silicon Detectors.

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.

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.

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.

USAF resolution targets consist of bars organized in groups and elements. Each group consists of six elements (i.e. elements 1-6) and each element is composed of 3 horizontal and 3 vertical equally spaced bars. Each element within a group corresponds to an associated resolution, based on the bar width/space. The resolution of an imaging system is defined by the group and element just before the black and white bars start blending together.

Note: Although the test yields precise resolution values, this is a qualitative test which depends on the user's definition of acceptable blur. The vertical bars are used to calculate horizontal resolution and the horizontal bars are used to calculate vertical resolution. One line pair equals one black and one white bar.

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.

The pattern on a positive target is most often made from a reflective material, such as chrome, deposited on a clear background. Positive targets can also be referred to as reflective targets since incident light hitting the chrome pattern will reflect. The pattern on a negative target, on the other hand, is clear and the background is chrome. Negative targets, or “transmission targets”, are most often used with a backlight in order to increase contrast between the target and the background. In terms of a technical difference, both types of targets will have the same maximum resolution regardless of their reflective or transmissive construction.

The choice of adhesive depends upon your application. Adhesives can be classified into two groups: optically opaque adhesives and optically transparent adhesives.

Optically opaque adhesives are used when light is not going to be transmitted through the adhesive, such as when bonding a mirror to an aluminum mount. Milbond and Loctite® are two such adhesives. Milbond adhesive, for example, uses two bonding agents that, when combined, create the adhesive. There is also a decementing agent available for Milbond that allows the adhesive to be removed when necessary. These type of adhesives do not require UV light in order to cure.

Optically transparent adhesives allow light to transmit through and are commonly used to bond lenses together. The Norland and Summers lines are two such adhesives. When cured with a UV light source, the adhesive has a defined index of refraction which we list under the specifications of each adhesive. Please note that UV adhesives such as Summers and Norland do not come with decementing agents and are very difficult to break the adhesion once cured.

Yes. UV adhesives are optimized to cure under UV light. UV adhesives absorb UV light and pass the visible and IR portions of the spectrum. However, since sunlight and most room lights also emit in the UV, the adhesives will cure under these conditions. Please note that initial and full cure times will be considerably longer, because there will be less energy spread over a larger area then when compared to a UV curing light source.

The most common adhesive we use for bonding our prisms is Norland NOA61. It is low-shrink (so the pieces won't move as it cures) and has excellent bonding strength for glass-to-glass. The adhesive is UV cured, so you'll need a UV source to make it stick. Once cured the adhesive is opaque to UV light but still works great if you are going to use the glued prism pair for visible or NIR applications, in other words, you can expect high transmission from 400 - 2000nm.

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.