n is the refractive index of the media in the object space (between the cover glass and the objective’s front lens) and θ is half the full angular aperture. The value of n varies between 1.0 for air and 1.58 for most immersion media used in optical microscopy. The angular aperture, which varies with the objective focal length, is the maximum angle of image-forming light rays diffracted by the specimen that the front lens of the objective can capture when the specimen is in focus. As the objective focal length decreases, the maximum angle between the specimen and the outer diameter of the objective front lens increases, causing a proportional increase in the angular aperture. From the above equation, it is obvious that the NA increases with both the angular aperture and the refractive index of the imaging medium.

Numerical apertureof lens

A telephoto field of view is great for zooming in on a particular subject and capturing crisp details, but it’s nearly worthless for monitoring a room or outdoor space.

Numerical Aperturecalculator

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A security camera viewing angle is how much a camera can “see” of the 180 degrees in front of it. It’s closely connected to the size of the lens. The bigger the lens, the smaller the field of view, but the more detail you’ll be able to capture.

A superwide-angle (aka ultra-wide) FOV captures the full 180 degrees in front of it. Some of them can even see the entire 360 degrees around them.

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Deep Sentinel offers wireless security cameras with a resolution of up to 1080p and a 130-degree field of view, PoE 4K ultra-HD dome cameras with an 89-degree viewing angle, PoE 2K ultra-HD dome cameras with a FOV of 112 degrees, and PoE 2K ultra-HD bullet cameras with a 114-degree viewing angle. No matter your particular needs, Deep Sentinel has you covered.

If you’re looking for coverage of a large area like your backyard or parking lot but aren’t overly concerned with the crispness of the image, you can stop here. Just be aware that superwide-angles don’t usually capture enough detail to identify individuals.

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A wide-angle camera checks the most boxes: field of view up to 110 degrees—sometimes even more—without the distortion that comes with a superwide-angle. And while it shows less detail than a standard or telephoto viewing angle, you can make up for some of that with a higher resolution—the number of pixels per inch—and quality components. A high-definition camera with a resolution of 1080p, 2K, or 4K can boost image clarity without having to sacrifice too much from the field of view.

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A super-telephoto FOV is used primarily by journalists and photographers that want stunning detail captured from a great distance. Think wildlife photographer shooting a pride of lions on the savannah or the paparazzi trying to sneak a picture of a celebrity vacationing on a private island.

Numerical apertureof objective lens

Notice how objects appear sharper and closer to the camera than in the 90-degree photo above, but some items like the garbage cans and cars in the foreground are no longer visible.

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With a range typically between 60 and 110 degrees (or more), a wide-angle FOV sacrifices some coverage for better detail. It’s ideal for security cameras in that sense.

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Are you willing to sacrifice coverage for clarity? Are you willing to sacrifice clarity for coverage? What are your needs?

The brightness and resolution of an image formed by an objective at a given magnification increases with its NA value, respectively the diameter of the angular aperture (the angle of the light cone collected by the objective). Light rays emanating from the specimen pass through air (or a liquid-based immersion medium) located between the cover glass and the objective’s front lens. The angular aperture is expressed as the angle between the microscope’s optical axis and the direction of the most oblique light rays captured by the objective (see the tutorial figure). Mathematically, the NA is expressed as:

Numerical apertureunit

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Sometimes you’ll want a wide field of view, and sometimes you’ll want a narrow one. But it’s vital that you pick the correct one for the job.

A camera is a camera is a camera, right? Yes. And no. While they all basically function in the same manner, cameras can differ in important but often forgotten ways. Camera A might be perfect for a task that Camera B can’t or shouldn’t do. For example, take the camera field of view (FOV), also known as the viewing angle. You’ve likely seen it listed in degrees as part of a camera’s specs. But what exactly is it?

Numerical apertureof microscope

The tutorial displays a schematic drawing of a microscope objective. The actual angular aperture of the light cone and the corresponding NA value are indicated in the tutorial window. To operate the tutorial, use the Numerical Aperture slider to change the NA value from low (left) to high (right). As you vary the numerical aperture value with the slider, the size and shape of the illumination cone entering the objective’s front lens is altered. The adjustable NA for this tutorial is 0.03 to 0.95. The approximate objective magnification has also been assigned to each NA value.

Too high, and it may be too far away to capture specific details. Too low, and you’ll lose coverage. You’ll have to experiment.

But at only 1 to 10 degrees in coverage, a would-be thief would literally have to stop on a marked spot far away and smile for it to be of any use in security. You’d have to hope burglars happened to walk through the very narrow field of view by sheer luck.

Are you curious about how microscope objectives capture finer object structures to produce higher-resolution images? This foundational knowledge article on Numerical Aperture and Light Cone Geometry will give you a sound understanding of the light gathering ability of microscope objectives and how it is expressed through the numerical aperture (NA). An interactive tutorial allows you to visualize changes in the illumination cone as you vary NA values. You will also learn about the role of the refractive index and the limitations of the maximum achievable NA values.

That may sound ideal for security purposes, but there’s a catch. A superwide-angle camera warps the image and creates a fisheye effect like you see when looking through a peephole. They can be useful when you want to capture as much of the scene as possible, but it comes at the expense of some detail and clarity.

The light gathering ability of a microscope objective is quantitatively expressed in terms of the numerical aperture (NA). The objective’s NA is a measure of its ability to capture image-forming light rays: Higher NA values allow increasingly oblique rays (representing finer object structures) to enter the front lens of the objective, producing a higher-resolution image with greater specimen detail. This interactive tutorial demonstrates the change in numerical aperture light cones displayed by a microscope objective with corresponding changes in numerical aperture. The angular aperture value corresponding to a given NA-value is also depicted here.

Camera height and positioning are crucial, too. Finding the right height for your camera—generally, either tabletop or up high, looking down—will allow you to maximize the FOV that you’re working with.

Numerical aperture nacalculator

Numerical apertureformula

To see that in action, grab your smartphone, open the camera, and point it at whatever is in front of you. The camera “sees” part of the scene, but not the whole thing. Next, zoom in on something. You’ll be able to recognize greater detail, but you’ll have even less of the scene on your screen. The viewing angle has shrunk.

As the name implies, this is the field of view for most cameras. It has a viewing angle of 25 to 60 degrees. You’ll only capture one-third of the scene at most, but with much greater detail and clarity, as objects and people appear closer to the camera. As far as security goes, a standard angle can be quite effective in a small room or if you’re only interested in capturing a specific section of the overall scene.

By experimenting with security camera placement, you can usually reduce or eliminate the blind spots created by the reduced field of view. For example, a camera mounted high in the corner of a room will capture most, if not all, of the scene, but one mounted in the middle of a wall will have blind spots on both sides of it.

Theoretically, the maximum angular aperture achievable with a dry (air) microscope objective would be 180 degrees, resulting in a value of 90 degrees for the half angle used in the NA equation. The sine of 90 degrees is one, indicating that the numerical aperture is limited not only by the angular aperture but also by the refractive index of the imaging medium. Most microscope objectives are designed to operate with air (refractive index= 1.0) as the imaging medium between the cover glass and the front lens of the objective. This yields a theoretical maximum NA of 1.00. For practical reasons (available working distance), the highest desirable value for the NA of a dry objective is 0.95 (the half angle of the aperture is approximately 72 degrees). Immersion objectives achieve much higher NAs at the expense of free working distance and spherical aberration sensitivity.

A camera’s field of view is not an independent variable. The size of the lens, the physical distance between the camera and the subject, mounting height, and placement all affect it. Your job—or the job of the security personnel you hire—is to consider them all.

Experiment with camera placement. Corners in a room and outside edges of a building where two walls come together are usually your best bet, but your unique situation may demand something different.

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At this point, the usefulness for security purposes plummets. With a range between 10 and 25 degrees, the field of view on a telephoto camera is just too small, despite the fact that it captures subjects in much greater detail.

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