Surface roughness has significant implications in various applications. For instance, in mechanical engineering, the surface roughness of a component can affect its friction characteristics, wear resistance, and ability to retain lubricants. In the electronics industry, the surface roughness of semiconductor materials can influence the performance of electronic devices. In the biomedical field, the surface roughness of implants can affect cell adhesion and tissue growth. Therefore, understanding and controlling surface roughness is crucial in many areas of science and technology.

You will notice that the circles in the pattern will move a certain direction when a specific screw is loosened or tightened. The more you do it, the more it makes sense. Just remember the “push/pull” effect the collimation screws have on the mirror. If the diffraction pattern needs to move from a different side than what you adjusted, pick a different screw to adjust, and see which way the circles move. It take a bit to get the hang of it, but if you do it right, it’ll work!

Stars are the best way to really check your telescope’s collimation, because, well…that’s what we need to have in perfect focus for those perfect photos. Or even half-decent photos. No focus, no photo, big problem.

Challenges in measuring surface roughness include the inherent variability of surfaces, limitations of the measurement methods, complexity in interpreting the measurement results, and managing the large volumes of data generated by the measurements.

Areal parameters (indicated by the letter S followed by another character) relate to measurements across a surface and are standardized using ISO 25178-2:2021, a “document [that] specifies parameters for the determination of surface texture by areal methods.” Optical non-contact techniques can be used for areal measurements. A 2021 study suggests that “areal measurement achieves better results, since a higher number of measuring points are included and the measuring field is independent of direction.”[3]

Without getting into the crazy but cool scientifical physics and math of it, collimation is, simply put, the physical alignment of your telescope’s optics. If your telescope is not properly collimated, it will be impossible to properly focus, no matter the sky conditions. Period. That’s all folks.

Surface roughness is a critical aspect of many industrial processes, as it can significantly impact the performance, quality, and functionality of manufactured products. In this article, we will explore the concept of measuring surface roughness, its importance in various industries, and the methods used for measurement. We will also discuss the challenges associated with measuring surface roughness and how to interpret the results of these measurements. By understanding the principles and techniques involved in measuring surface roughness, professionals can make informed decisions to optimize their manufacturing processes and improve product quality.

[…] a few different ways to determine whether or not you can see your binoculars in collimation. Some collimation issues may not be visible with the naked eye, but they may be visible at night. Collimation problems may […]

[…] if you make the binoculars wider or narrower to fit another person’s eyes. One of the most difficult collimation issues to detect is involuntarily, but it is more easily detected at night. When you see two images with […]

Surface roughness, in a technical context, refers to the fine irregularities on the surface of a material. These irregularities can be a result of the manufacturing process, wear, or even the nature of the material itself. For example, a machined surface may be very different to an extruded surface, even if the material is the same. The scale of these surface irregularities can range from the microscopic level, such as the grain structure of the material, to the macroscopic level, like visible scratches or pits.

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One of the first steps in interpreting surface roughness measurements is to compare the measured parameters to the specified tolerances for the part. This involves checking whether the measured values fall within the acceptable range defined by the design specifications. If the measured values are outside the specified tolerances, it may indicate a problem with the manufacturing process or the material itself.

Note: If one of the adjustment screws starts to feel tighter than you think it should, rather loosen the screws on the opposite side instead.

In some cases, the interpretation of surface roughness measurements may require the use of advanced statistical analysis techniques, such as regression analysis or machine learning algorithms. These techniques can help identify patterns and relationships between the measured parameters and the part's performance, allowing for more accurate predictions and optimization of the manufacturing process.

Is your telescope not performing? Keep reading. Want a quick and dirty way to check and tune your telescope’s collimation? Keep reading. Do you only have a refractor telescope? You can keep reading for fun, but there’s not much you can do about collimation. Don’t blame me for that…

What is collimationof a telescope

There are several methods used to measure surface roughness, each with its own set of principles, advantages, and disadvantages. These methods can be broadly categorized into contact and non-contact methods.

There are a few different collimation tools available. Lasers, cheshire eyepieces, etc. I’ve used two different laser collimators, I’ve done some modifications using paper and special caps, and even used my eyes to try and get it right. It’s difficult, it can take a LONG time until you get the hang of it. While the tools will usually get you pretty close, and sometimes, if you’re lucky and good, nearly dead-on, that’s usually where it ends.

Repeat the steps above for until you are able to move the diffraction pattern in a predicted way and you are able to get the circles as concentric as possible. You want even gaps all the way around, as perfect as you can get.

The most common parameter used to describe surface roughness is Ra (arithmetic average roughness), which is the average of profile height deviations from the “mean line” — the reference line that deviations are measured from. This is a useful measurement when using a 2D measurement system like stylus profilometry, though it is arguably less useful than areal parameters like the equivalent Sa. Other parameters indicate values such as the maximum height of peaks and valleys, measured in micrometers or microinches.

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Co-founder of PhotographingSpace.com, co-owner of several telescopes and mounts, too many cameras, and not enough hard drives, Cory is an American expat living in South Africa with his wife, Tanja Schmitz.

Mirrored optical telescopes like the Newtonian, SCT, RC, etc., will have a secondary mirror mounted on the business-end of the telescope tube (the front), held in place by either a “spider”, a glass pane, or some other method. On this, there will be adjustment screws, usually three of them, evenly spaced. Find those, carefully.

What is collimationin surveying

Stylus profilometry is known for its high accuracy and repeatability, making it suitable for a wide range of applications. However, it has some limitations, such as the potential for the stylus to damage delicate surfaces. Additionally, the method is inherently slow due to the need for physical contact and movement across the surface, which can be a disadvantage in high-volume manufacturing environments.

NOTE: This quick tutorial is geared toward telescopes with mirrored optics, specifically those with a secondary mirror that allows for adjustment. Like a Newtonian, Ritchey Chretien, SCT, etc. While all optical instruments need collimation, refractors are typically not able to be adjusted outside the factory. This is NOT a full collimation tutorial, because you may also need to adjust the primary mirror, if things are really bad, but I’m not covering that here.

An avid astrophotographer for timelapse, deep-space imaging, lunar, planetary, and star trail imagery, he is an all-around jack-of-most-trades for night-sky photography.

[…] methods can be used to determine whether or not your binoculars are out of alignment. In general, collimation issues can be identified more easily at night by looking in the naked eye, but some can also be identified […]

[3] Schmidt J, Thorenz B, Schreiner F, Döpper F. Comparison of areal and profile surface measurement methods for evaluating surface properties of machined components. Procedia CIRP. 2021 Jan 1;102:459-64.

Collimating lens

Profile parameters (indicated by the letter R followed by another character) relate to measurements of roughness along a line, calculated using a roughness profile obtained from a 2D measurement process such as stylus profilometry. They are standardized using ISO 21920-2:2021, a “document [that] specifies terms, definitions and parameters for the determination of surface texture by profile methods.”

Contact methods involve the use of a probe or stylus that physically interacts with the surface being measured. The probe moves across the surface, and the vertical displacement of the probe is recorded as it encounters the surface irregularities. This data is then used to calculate surface roughness parameters. One of the most common contact methods is stylus profilometry.

Collimated beam

The theory behind this is simple: those three screws will allow for a push/pull effect on the secondary mirror, allowing you to aim the light properly as it is reflected from the secondary mirror onto the camera sensor. Tightening (pulling) or loosening (pushing) will move the secondary mirror on the side where the screw is, which allows you to push or pull the circles in the diffraction pattern from that particular direction.

The measurement of surface roughness is a key quality control process that can significantly impact the performance and lifespan of a product. For instance, in mechanical components, a high level of surface roughness can lead to increased friction, rapid wear, and premature failure. Conversely, a surface that is too smooth may not retain sufficient lubrication, leading to increased friction and wear. Researchers have shown that “lubricant load carrying capacity is largely affected by surface texture, roughness, and their interactions.”[1]

Measuring surface roughness presents several challenges, which can be attributed to the nature of the surfaces being measured, the measurement methods used, and the interpretation of the measurement results.

Another important aspect of interpreting surface roughness measurements is understanding the impact of the measured parameters on the part's performance. For example, in mechanical components, if the highest peak is well above the mean line, the surface may suffer increased friction and wear that leads to issues like galling, while a surface that is too smooth — or one whose lowest valleys are not especially deep — may not retain sufficient lubrication. In such cases, it is essential to understand the relationship between the surface roughness parameters and the performance characteristics of the part, such as friction, wear, and lubrication retention.

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Interpreting surface roughness measurements involves understanding the relationship between the measured parameters and the performance of the part in its intended application. This requires a thorough understanding of the surface roughness parameters, as well as the specific requirements of the application.

The interpretation of surface roughness measurements also presents challenges. The surface roughness parameters provide a mathematical description of the surface, but relating these parameters to the part's performance in its intended application can be complex. This requires a deep understanding of the relationship between surface roughness and functional properties such as friction, wear, and sealing ability, which can be influenced by a multitude of factors beyond the surface roughness itself.

In the electronics industry, the surface roughness of semiconductor materials can directly influence the performance of electronic devices. High surface roughness can lead to increased electrical resistance, reduced electron mobility, and increased heat generation, all of which can degrade the performance and reliability of electronic devices.

Despite these limitations, stylus profilometry remains a popular choice for surface roughness measurement due to its proven reliability and the detailed information it provides about the surface profile. It is used in a wide range of industries, including automotive, aerospace, electronics, and biomedical, to ensure product quality and performance.

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Atomic force microscopy (AFM) is another non-contact method used to measure surface roughness at the nanometer scale. AFM works by using a sharp probe, known as a cantilever, that is positioned close to the surface without touching it. As the probe scans the surface, the attractive and repulsive forces between the probe and the surface cause the cantilever to deflect. This deflection is measured using a laser beam that is reflected off the cantilever and onto a photodetector.

In the biomedical field, the surface roughness of implants can significantly affect their interaction with biological tissues. A surface that is too smooth may not promote cell adhesion and tissue growth, leading to poor integration of the implant with the surrounding tissue, while a surface that is too rough may cause excessive tissue reaction and inflammation. On the other hand, some researchers have noted that the “details of the textured surfaces can be more determining on cell adhesion and proliferation, rather than their roughness degree.”[2]

Collimationcap

Optical profilometry is a non-contact method that uses light to measure surface roughness. One type of optical profilometry works by projecting a structured light pattern onto the surface and capturing the reflected light with a camera or detector, though other light sources such as lasers can also be used. The distortion of the reflected light pattern provides information about the surface topography, which can be used to calculate surface roughness parameters.

I’ve been gearing up for this year’s major planetary oppositions, where Jupiter, Saturn, and Mars are the largest apparent size in our sky, so the time of year when they are prime astrophotography targets. Doing this has spurred me on to get out our longest focal length telescope (a GSO 12″ F/8 Ritchey Chretien) and do some testing. At first, I was severely disappointed; focus issues made the the first couple of nights out a nearly soul-destroying experience, but I kept at it. And, I fixed it. Here’s how.

[1] Bachchhav B, Bagchi H. Effect of surface roughness on friction and lubrication regimes. Materials Today: Proceedings. 2021 Jan 1;38:169-73.

One of the primary challenges is the inherent variability of real-world surfaces. Surfaces can exhibit a wide range of features, such as peaks, valleys, and waviness, which can vary significantly over the surface area. This variability can make it difficult to obtain a representative measurement of the surface roughness, especially for surfaces with complex geometries or heterogeneous material properties. This issue can be mitigated somewhat by using areal measurements, where the metrologist does not have to establish a single mean line from which to take measurements.

Houston, we’ve got a problem. Your collimation is out, that’s probably why you can’t focus. Try this quick and dirty method of adjusting the secondary mirror, which is always done first anyway. Note, this is NOT a full tutorial to fully collimate your telescope, because methods of collimation vary by the type of scope you have. However, this will give you an idea of how to get some quick results in the field if you are really annoyed with your focus.

Stylus profilometry is a widely used contact method for measuring surface roughness. It involves the use of a diamond-tipped stylus that is dragged across the surface at a constant speed. The stylus profilometer follows the surface contours along a line, and its vertical displacement is recorded by a high-resolution linear encoder. This displacement data is then processed to generate a surface profile and calculate surface roughness parameters.

Measuring surface roughness is important because it can significantly affect the performance of the part in its intended application. It allows for quality control during the manufacturing process and can help predict how the part will perform in terms of factors such as friction, wear, and sealing ability.

Another challenge is the limitations of the measurement methods themselves. For example, contact methods such as stylus profilometry can potentially damage delicate surfaces, while non-contact methods such as optical profilometry may struggle with surfaces that are highly reflective or have steep slopes. Furthermore, all measurement methods have inherent uncertainties, which can be influenced by factors such as the calibration of the instrument, the environmental conditions during measurement, and the operator's skill and experience.

Surface roughness is quantified using a set of parameters that describe surface characteristics. These parameters are calculated from the surface data obtained from the measurement methods discussed earlier. Roughness parameters used in metrology can be divided into two groups: profile parameters and areal parameters.

[2] Rosales-Leal JI, Rodríguez-Valverde MA, Mazzaglia G, Ramón-Torregrosa PJ, Díaz-Rodríguez L, García-Martínez O, Vallecillo-Capilla M, Ruiz C, Cabrerizo-Vílchez MA. Effect of roughness, wettability and morphology of engineered titanium surfaces on osteoblast-like cell adhesion. Colloids and Surfaces A: Physicochemical and Engineering Aspects. 2010 Aug 5;365(1-3):222-9.

What is collimationin radiology

Surface roughness measurement is an important task in many industries, including manufacturing, materials science, and engineering. It involves a variety of methods, each with its own advantages and disadvantages, and requires an understanding of surface roughness parameters and how they relate to the performance of the part in its intended application. Despite the challenges associated with measuring surface roughness, advancements in measurement technology and data analysis techniques continue to improve the accuracy and efficiency of these measurements, enabling better quality control and optimization of manufacturing processes.

So, I don’t want to talk about those other tools right now. I want to talk about using the actual things we are trying to photograph, in the real conditions, in the field (or your backyard): a star.

What is collimationin x ray

He is also an internationally published and commissioned astrophotographer, where his photos have been used in multiple online and print publications.

Therefore, measuring surface roughness is not just about ensuring compliance with technical specifications. It is about understanding the relationship between surface characteristics and product performance, quality, and appeal. By accurately measuring and controlling surface roughness, manufacturers can optimize their processes, improve product quality, and meet the diverse needs of their customers.

Surface roughness can be measured using a variety of methods, which can be broadly categorized into contact and non-contact methods. Contact methods involve a probe that physically interacts with the surface, while non-contact methods use optical or electromagnetic principles to obtain surface information.

In addition to affecting product performance and quality, surface roughness can also influence the aesthetic appeal of a product. In industries such as automotive and consumer goods, where the visual appearance of a product is a key selling point, smooth surfaces are of paramount importance.

WARNING: DO NOT TOUCH the secondary mirror or any glass surface, and be careful to NOT DROP TOOLS into the telescope tube. Damaging either mirror is a risk and extreme care should be taken!

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The factors contributing to surface texture and roughness are numerous and can be broadly categorized into three groups: material factors, process factors, and environmental factors. Material factors include the inherent properties of the material, such as its hardness, ductility, and grain structure. Process factors encompass the methods and conditions of manufacturing, including the type of machining process used, the cutting tool geometry, feed rate, and cutting speed. Environmental factors that contribute to smooth or rough surfaces involve conditions like temperature and humidity during the manufacturing process, which can influence the material's behavior and thus the resulting surface finish.

How to collimate a Dobsonian telescope

Non-contact methods of measuring surface roughness do not require physical interaction between the measuring instrument and the surface. These methods typically rely on optical or electromagnetic principles to obtain surface information. Non-contact methods offer several advantages over contact methods, such as faster measurement times, no risk of damaging delicate surfaces, and the ability to measure a wider range of materials. Two common non-contact methods are optical profilometry and atomic force microscopy.

Surface roughness parameters like Ra are numerical values that describe the characteristics of the surface. They are calculated from the surface profile or areal data obtained from the measurement methods and can provide information about the vertical deviations of the surface, the distribution of the roughness over the surface area, and other characteristics.

Surface roughness refers to the fine irregularities on the surface of a material, which are typically caused by the manufacturing process. It is a key characteristic of the surface that can significantly affect the performance of the part in its intended application.

To check the collimation of your telescope using a star, either a real one or an artificial one, like this. Often, an artificial star is easier to use because it doesn’t suffer from atmospheric effects seen in the example images. However, it usually isn’t handy to use an artificial star in the field.

Optical profilometry offers several advantages over contact methods, such as faster measurement times, no risk of damaging the surface, the ability to scan an entire 3D area rather than a 2D line, and the ability to measure a wide range of materials, including transparent and reflective surfaces. However, it may be less accurate than contact methods for surfaces with complex geometries or steep slopes, as the light may not be able to reach all areas of the surface.

AFM provides extremely high-resolution measurements of surface roughness, making it suitable for applications in nanotechnology, materials science, and semiconductor manufacturing. However, AFM has some limitations, such as a relatively small scanning area and slow measurement times compared to other methods. Additionally, AFM requires a high level of expertise to operate and interpret the results, which can be a barrier to its widespread adoption.

Finally, there is the challenge of managing the large volumes of data generated by surface roughness measurements. Modern measurement instruments, especially optical devices, can generate high-resolution surface profiles consisting of millions of data points, which require sophisticated data analysis techniques to extract meaningful information. This necessitates the use of advanced statistical methods and machine learning algorithms, which can add complexity to the measurement process.