An action camera head mount is a mount or a strap that allows you to attach an action camera onto the top of your head so that you don’t need to hold it while carrying out your sporting activities. A head mount is one of the most common and best ways to attach an action camera to yourself and it is suitable for multiple different scenarios. During this article we will be looking at some of the best things about an action camera head mount, but also some of its drawbacks.

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Good Field of View: Since a head mount attaches the action camera to your head, your camera will basically capture whatever it is that you see in front of you, providing some extremely nice POV footage for whatever sport you are carrying out. By having the camera mounted to your head instead of your chest or shoulders, you ensure that the camera won’t be blocked by your hands, or any equipment you may be carrying that needs to be placed in front of you.

Modulation transfer function

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The first basic principle of through-focus MTF is the geometrical limitation. Any lens that focuses light produces an “illumination cone.” See below for an example:

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MTF

f/# (pronounced “EFF number”) is the focal length of a lens divided by the diameter of the beam of light that enters it. If you’d like to learn more about that concept, head to this page. For a simple lens, such as the one pictured above, the diameter of the beam is the diameter of the lens. More complicated lenses, like those on digital cameras, often have an entering beam diameter that differs from the lens diameter. The lens above has a focal length that’s twice the diameter of the entering beam, so the f/# is 2. This is written as f/2 (pronounced EFF two).

The light from the lens comes to a focus and then expands again, as it should. The diameter of the illumination cone (called the spot size) is very small at the focus but it is larger at either side. The following figure, called a “through focus spot diagram”, shows its variation on either side of focus.

According to the Petzval field curvature plot, the total field curvature from the center of the image (0 degrees) to the edge (9.4 degrees) is about 0.23 mm. We can measure the Petzval curvature on the corresponding through focus MTF chart by measuring the distance from the peak of the 0 degree line to the peak of the 9.4 degree line. These peaks as seen on the plot are about 0.15mm apart. The field curvature plot exaggerates the real field curvature by 150%! This is because Petzval field curvature plots rely on approximations.

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Unfortunately, the best focus for the light at the edge of the image (red) and even part way out (green) does not lie at the same place as it does for the center of the image. This condition, known as “field curvature”, is caused by one of two aberrations: Petzval curvature or astigmatism. See our Aberrations page to learn about these. Also, the sagittal and tangential curves do not peak at the same focal position. This is typical of astigmatism. However, the difference between the sagittal and tangential curves is much less than the difference between the center and edge of the image. This means your optical engineer would tell you that the Petzval curvature is more of a problem than the astigmatism. If you can’t get the entire image in focus at the same time, this is likely the problem. If you focus on the edge of the image, the center looks fuzzy (and vice versa) as seen here.

Action cameras are the filming device you should use when it comes to recording fast paced and action-packed events. Since action cameras are usually small and designed to withstand extreme conditions and heaps of punishments, they are perfect for sport enthusiasts and athletes who want to capture their sporting moments or highlights. However, taking stable and clear footage while avoiding injuries during the sport can extremely challenging to do. This is when an action camera head mount comes into the rescue. As many would there are numerous of different kinds of body mounts on the market, so what are the pros and cons of a head mount? We will be exploring in this as well as numerous other questions throughout this article.

MTFtest

Can be Extra Weight: For individuals that are not accustomed to head mounts, having an extra piece of weight (no matter how light) attached to your head, can be uncomfortable. You may need to constantly move or look around during your sports which having a head mount can slightly have an effect on your performance.

There are multiple types of different mounts and ways you can attach an action camera onto your body or equipment. Each of these methods come with their own pros and cons. An action camera head mount is by far one of the best mounts out of the plethora of choices there are for body mounts. That being said, action camera head mounts do also have their cons, they aren’t perfect. Let’s take a look at some of the pros and cons of a head mount for action cameras.

We can measure Petzval field curvature several different ways, but we prefer to rely on the through focus MTF plot. It generally gives the most accurate representation of the real field curvature. See the two plots below as an example. One is a plot of the through focus MTF and the other is a simple field curvature plot of the same lens. Both of these plots are for monochromatic light at 550nm.

Only good for POV Footage: If you are looking to specifically film something or work film someone else, an action camera head mount may not be the best choice. This is because since it is mounted onto your head, it records whatever you look at or see, and you are restricted to capturing things by the movement of your head. If you are looking to film things not in a POV perspective, then a head mount is probably not the choice for you.

Now that you understand the theoretical limit of through focus MTF, it’s time to get practical. A picture of the through-focus MTF of a real lens is displayed below.

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As before, the blue curve represents data from the image’s center, red from the edge, and green from in between. To get these curves, the user specifies a certain spatial frequency that’s commonly half to three fourths of the maximum. Then the user has the lens design software plot the variation of the MTF at this spatial frequency versus focus. The zero point is typically the “best focus” for the lens. The plot shows how fast the MTF falls off as the image plane moves from its optimal location.

Let’s start by observing the blue line. On it we can see that the MTF peaks at around 0.06 units to the right of the “best focus” and drops off on either side. The dropoff is not symmetric, which is common for systems with spherical aberration. For more information on aberrations, click here. Assuming that an MTF of 0.2 is acceptable, the image plane can be moved about 0.4 units to the left of best focus or 0.16 units to the right before the resolution at the center of the image is no longer acceptable.

The AKASO Brave 7 is a dual color screen, IPX8 waterproof, 4K 30 FPS action camera. With its innovative dual-color screens, bid farewell to the traditional single-screen, blind-shooting of regular action cameras. Easily tell your story and show off your exciting moments. Since its IPX8 waterproof to 5M/16FT with no external case, making riding in the rain, playing in the water, swimming, surfing, snorkeling and other water sports safe and easy. The AKASO Brave 7 can fit all your action-packed filming needs with its six-axis, anti-shake technology（EIS 2.0）can shoot smooth (as well as smooth out) images and hold every moment steadily despite vigorous movement. The AKASO Brave 7 has a 170-degree super wide angle, much larger than that of a mobile phone. It also supports 70/110/140 viewing angles, allowing for the best shooting angle for stories, vlog or a movie. At only the price of $169.99, you are able to take this all-rounded action camera home with you to shoot the best action-packed content.

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Now that we have discussed and looked over the pros and cons of an action camera head mount. Some may ask what is a good action camera to go with a head mount? With multiple different choices and brands out there, it can be a hard choice to make. Today we will be introducing one of the best action cameras out there, the AKASO Brave 7.

The Petzval curvature plot doesn’t always differ significantly from the through focus MTF plot, but it’s always a good idea to specify the maximum allowable focal shift in MTF when designing a custom lens. This is because just specifying the Petzval curvature approximation may differ significantly from the real field curvature.

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Now that you understand MTF, the next important concept is how refocusing a lens affects it. This is called the through focus MTF. It is important that you get this information from your optical engineer, because without it you could end up with an optical system that does not meet your needs.

Safety: Having the action camera mounted to your head is by far one of the safer options as it is close to your body and not dangling around as one would with a shoulder mount or a bite mount. With the action camera on your head, you free up your hands and you can focus on your sport without needing to worry about the camera getting in your way as it is closely mounted on your head. This will largely increase the safety of yourself while wanting to record your sports, as you will essentially be able to do two things at once.

The spot size at a given distance from focus can never be smaller than the diameter calculated from the f/#. Take, for example, the f/2 lens shown above. The spot size 1 mm away from the focus can never be smaller than 1/2 mm. If the lens were f/2.5, the spot could be no smaller than 1/2.5 or 0.4 mm. Applying what we learned about MTF, the MTF at 2 cy/mm would be essentially zero for an f/2 lens 1 mm from focus. An f/2.5 lens would have a nonzero 2 cy/mm MTF at 1 mm from focus, but it would drop to zero at 1.25 mm from focus.

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In this article we discussed and explored the different pros and cons an action camera head mount may have.  Action Cameras are the digital film capture devices currently available for capturing sport scenes or anything that is fast paced. Action camera head mounts or just any body mount as a matter of fact are a must have for attaching the camera onto your body so that you can focus on the sport safely and film good footage at the same time. If you are interested in checking out AKASO’s Brave 7 Action Camera, feel free to check the following link: https://www.akasotech.com/brave-7. Thank you for reading!

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The central spot is at the focus of the lens and the spots to the left and right correspond to the illumination cone before (to the left) and after (to the right) focus. As you can see, the spot size increases dramatically as you move away from focus. This forms an upper limit on the through focus MTF. The F# of the optical system will determine how fast this happens. Any photographers reading this may be familiar with this term, but let me explain it for the others.

Compatible with Most Sports: Something like a chest mount or a shoulder mount may not be suitable for most sports. First, for something like biking, your hands may get in the way and block the footage. In other instances, a chest or shoulder mount can feel constricting, which will affect your movement in some sports. An action camera head mount fixes this issue as having it mounted onto your head will most likely never get into the way with any of your sports, not to mention that they are compatible with almost any sport that needs a helmet, as all you need to do is instead of using a head strap mount, you mount the action camera to your helmet.

Through-focus MTF can be used to determine the depth of focus for a lens. In the above plot, all three fields have an MTF above 0.2 from -0.14 units to +0.07 units. This means that the total depth of focus is 0.21 units. If the units are mm, this would be very easy for a mechanical designer to accommodate, but if the units are microns, it would be exceedingly difficult. That’s why it’s important for your optical engineer to communicate this information to you as you design your optical system.

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