AOV (angle of view) vs FOV (field of view) explained

[Dashmellow]

FOV vs AOV
​

For some reason, the term FOV (Field of View) has become the default term everyone uses to describe how wide or narrow a view is provided by the lenses that come installed on our dash cams, even though this is technically incorrect terminology for describing this. We all do it, even me at times. The correct term is AOV (Angle of View). AOV is an optical lens specification that characterizes each and every lens whereas FOV is not as it is a relative term.

We can mostly thank dash camera manufacturers and retailers for this, along with other misinformation that is regularly spread by the industry for marketing and sales promotional purposes. (more on this at a later date). Somehow FOV has become embedded in everyone's brain as the default term because it kind of sounds about right and partly thanks to widespread use on the internet it is the term everyone uses even though it is inaccurate.

Typically, you'll see the term FOV used incorrectly in marketing, like this promotion for a video doorbell camera.



So, this thread is an attempt to clarify the definitions of AOV & FOV in the service of educating our membership in the hope that it moves the knowledge needle forward a little.

Field of View (FOV) is the extent of the observable world that is seen by a lens at any given moment.

Angle of View is the decisive variable for the visual perception of the world seen by a given lens.

In other words, every lens of a given focal length will have only one angle of view but the same lens can have many fields of view according to what it is pointed at.

Angle of View (AOV) has to do with the focal length of the lens and is a measurement in degrees of how wide the frame will be from the front of the camera lens. This is why a “wide angle lens” covers a wide area with “angle being the operative word. AOV will always be fixed with each primary lens and never changes. It is strictly a function of the focal length of the lens expressed in degrees to describe the coverage the lens can observe.

You will never see a standard wide angle lens described as a “wide field of view lens”, hence this post.

Field of View (FOV) is variable. In photography, the field of view is that part of the world that is visible through the camera at a particular position and orientation in space. This means it is simply a measurement of how much a lens can frame depending on how far away the camera is from the subject and this is why using the term FOV to describe the overall frame coverage of a lens in degrees is wrong, especially with dash cams as the FOV is constantly changing as we drive and because of this we see many fields of view as we travel around in our vehicles. As such, the FOV when you are right behind another car in bumper to bumper traffic will be different than the FOV when you are driving on an open highway with the horizon way out in front of you.

FOV is often referred to as the "solid angle of scene opposite the camera lens".

If you park your car facing a brick wall only 20 feet away with a typical dash camera, the frame captured by your camera is your FOV (solid angle of scene opposite the camera lens).

If you park the same car with the same dash camera facing a football field or an ocean, the frame captured by your camera will also be your FOV (solid angle of scene opposite the camera lens).

So again, Angle of View is an optical lens specification and it is fixed and finite and is entirely a function of the focal length of a specific lens which is what determines the overall angle of coverage in degrees that can be captured any given lens.

Field of View is variable and is determined entirely by the distance to the subject within the angle of view. So unlike AOV it is not a specification describing a specific brand, coverage and design of lens, it is merely a situational measurement describing what that lens can see at that moment at that particular distance.

AOV - Angle of View - measured in degrees.

FOV - Field of View - measured in linear units and also often expressed in degrees.

Field of View is a term commonly and correctly used with binoculars. You might see a binocular’s FOV (or AFOV angular field of view or LFOV linear field of view) specifications described as - something like, Linear Field of View “330 feet/1000 yards - AFOV - 6.3 degrees” (AFOV refers to what can be seen at a given distance). This means that looking through binoculars at a scene 1000 yards away you will see a FOV 330 feet wide (horizontal). Looking through the same pair of binoculars at a subject at a closer distance of 500 yards you would see a much smaller area at greater magnification and therefore a smaller AFOV. Unlike the dash cam industry, binocular manufacturers have this terminology correct, in part because the nature of how binoculars are used requires it. Field of view will decrease with higher magnification in the same way you see less through a telescope or telephoto lens (which have a very narrow AOV - Angle of View) but the FOV increases and widens when you're looking at something much farther away.

Field of View can be measured horizontally, vertically and diagonally. This usually refers to how images are captured but sometimes refers to how images are displayed.

You will sometimes see the following acronyms used.

HFOV: Horizontal Field of View
VFOV: Vertical Field of View
DFOV: Display or Diagonal Field of View
AFOV: Angular Field of View

AOV and FOV are closely related and indeed joined at the hip within the same lens. In fact, there is a direct and vital relationship between AOV and FOV, as one does not exist without the other, thus, you can convert one to another using basic high school trigonometry.

The formula that is most commonly cited for calculating lens angle of view is:

Angle of view (in degrees) = 2 ArcTan( sensor width / (2 X focal length)) * (180/π)​

You would calculate FOV using the equation:

Field of view = 2 (Tan (Angle of view/2) X Distance to Subject)​

These simple formulas are basic high school level trigonometry.


AOV can be measured horizontally, vertically, or diagonally, although for most photographic purposes it is usually measured diagonally.



If you don't want to read the entire explanation above, this graphic will tell you all you really need to know about the difference between AOV and FOV.

 

[Panzer Platform]

This is exactly what I've been saying since day one. lol

 

[Dashmellow]

This is exactly what I've been saying since day one. lol

What you've been saying since day one is that it's not worth trying to feed dash cam users anything but the most simple of concepts or even completely incorrect concepts because it is easier for them to grasp. I really don't know why you keep promoting the idea that people are inherently dumb and have no interest in learning anything new, especially on a forum like this. It's odd Chuck, but the notion of an Idiocracy seems almost aspirational for you which makes me feel sad, especially coming from a guy who spends all his time on the forum doing technical evaluations of dash cams. I've debated about saying what I'm saying here but for two weeks now every time I mention something innovative or interesting you take issue with me and keep pounding the table about it, accusing me of "over-complicating things".? The last time you repeatedly had a problem with my suggestion that dash cams could benefit from having a low, medium and high volume control because to you that would be too much for the average person to handle, even though these are the very same people who can handle all kinds of sophisticated settings on their smartphones. And if this were true, why do you bother spending so much time posting dash cam current and voltage measurements, infra-red photos and all kinds of other arcane technical data and dash cam information on the forum here, as most members you are doing these elaborate and sophisticated camera reviews for are those same people who really just come to this forum for basic, straightforward advice about which camera to purchase? Perhaps you are the one over-complicating things, along with engaging in a double standard?

​

 

[Dashmellow]

Here are a couple of AOV / FOV Visualizers. The are kind of fun to play with and can be helpful in learning these concepts.

Camera - AOV & FOV​

AOV & FOV visualizator​

 

[TonyM]

I was curious about the information provided by dashcam vendors on their websites, so I looked at a few examples from some of the well-known brands:

BlackVue get off to a good start, quoting the diagonal, horizontal and vertical AOV for their DR970X-2CH.



Viofo only state a "viewing angle" for their A139 Pro 3CH. This image on their website suggests these are Horizontal AOV figures. And yes, there's a discrepancy between 165° and 170°.





Vantrue has no spec list for its N4 Pro, but this graphic appears to suggest Horizontal AOV values for all 3 channels.




Nextbase only quote a single angle for their 622GW. This is probably a Horizontal AOV, but it certainly is not clear.


Of course, these quoted values are only useful if they are accurate. From personal experience, and reading numerous review threads here on DCT, it is often the case that two cameras with a "140° viewing angle" do not have the same Angle of View - even when comparing products from the same manufacturer.

 

[Dashmellow]

I'm pleased to hear that some dash cam manufacturers are using the term "viewing angle" as it is more accurate than "field of view". On the other hand, "viewing angle" is really just a vague term the way it is used by manufactureres that doesn't specifically mean anything definitive compared to the actual optical term or specification used by engineers and lens designers, i.e. - Angle of View. AOV is generally measured on the diagonal, although as shown above can also be measured on the horizontal or vertical. Another factor here is how often manufacturers or retailers present a "viewing angle" number that often seems to have nothing to do with how the lens on any given camera actually performs. We see claims made about dash cam lens coverage the doesn't match what we see in the videos produced by these cameras. This is why I consider terms like "viewing angle" to often be more about marketing than actual specification.

If you were to take the time to comb thousands upon thousands of posts here on DCT you would universally find members, retailers, manufacturers and professional camera reviewers using only the term FOV. You would find pretty much the same on Amazon and elsewhere on the internet. FOV has become the default even though it is a misnomer. I used to do the same but changed to using the term AOV approximately a year and a half ago when I realized it was a much more accurate and specific definition. @TonyM also started to use the term AOV after I brought this concept to his attention in a small group PM chat we both participated in back in March, 2022. As far as I am aware, we are the only two using the correct term here on the forum.

March 9, 2022


Anyway, as I've been trying to explain, unlike something like FOV which is variable, or "viewing angle" which as presented to us is vague and often ill-defined, the term AOV is a definition and specification used by optical designers and high end lens manufacturers. Whether anyone else here on the forum will eventually start using the correct term, I wouldn't know, but AOV is the correct terminology.

For example, when you shop for a high end lens you will usually see the actual AOV specification and measurement in degrees, often including the angle direction used for the measurement.

 

[Leonauto]

FOV vs AOV
For some reason, the term FOV (Field of View) has become the default term everyone uses to describe how wide or narrow a view is provided by the lenses that come installed on our dash cams, even though this is technically incorrect terminology for describing this. We all do it, even me at times. The correct term is AOV (Angle of View).​

You did an interesting study - an explanation of "who is who" and how to call it correctly.

For my part, I would like to note that in the Russian version the "viewing angle of the dashcam" has always been called the "Angle of View", apparently due to the peculiarities of the translation and the specifics of the language, probably ...

And the measurement of the horizontal viewing angle was earlier in almost every review of the dashcam. There was a special table according to which these measurements were taken.
How to measure the horizontal AOV of the dashcam on your own at home? You can drive up to any flat wall as perpendicular to it as possible and take two measurements - the distance from the dashcam to the wall and the distance in width between the extreme points that are captured by the dashcam (to do this, you need to open a screenshot of the video of the moment the wall was filmed and remember these extreme points on video, so that later on a real wall to measure between them).
Calculator for automatic counting the horizontal Angle of View (in the car) -> AOV Calculator

To simplify the calculations, one of the enthusiasts of the Russian VR-forum created a calculator that allows you to automatically calculate the AOV of the dashcam without any calculations, having only the distance to a flat wall and the width of the captured image.
Calculator here: https://dim565.ru/angle/

Or the capture width can be set in advance - for example, put two columns (or two other landmarks), as in the example on the site with a calculator, and drive up to them at a distance when the landmarks are at the very edges of the frame. You have the distance between the landmarks (size b), all that remains is to measure (size a) from the dashcam to an imaginary line connecting these two landmarks.

However, there is also a laboratory method, which differs from measurements on a flat wall or on two columns, about this - an additional post, later.

 

[Dashmellow]

You did an interesting study - an explanation of "who is who" and how to call it correctly.

For my part, I would like to note that in the Russian version the "viewing angle of the dashcam" has always been called the "Angle of View", apparently due to the peculiarities of the translation and the specifics of the language, probably ...

And the measurement of the horizontal viewing angle was earlier in almost every review of the dashcam. There was a special table according to which these measurements were taken.
How to measure the horizontal AOV of the dashcam on your own at home? You can drive up to any flat wall as perpendicular to it as possible and take two measurements - the distance from the dashcam to the wall and the distance in width between the extreme points that are captured by the dashcam (to do this, you need to open a screenshot of the video of the moment the wall was filmed and remember these extreme points on video, so that later on a real wall to measure between them).
View attachment 65725 Calculator for automatic counting the horizontal Angle of View (in the car) -> AOV Calculator

To simplify the calculations, one of the enthusiasts of the Russian VR-forum created a calculator that allows you to automatically calculate the AOV of the dashcam without any calculations, having only the distance to a flat wall and the width of the captured image.
Calculator here: https://dim565.ru/angle/

Or the capture width can be set in advance - for example, put two columns (or two other landmarks), as in the example on the site with a calculator, and drive up to them at a distance when the landmarks are at the very edges of the frame. You have the distance between the landmarks (size b), all that remains is to measure (size a) from the dashcam to an imaginary line connecting these two landmarks.

However, there is also a laboratory method, which differs from measurements on a flat wall or on two columns, about this - an additional post, later.

Thanks for the encouraging comments.

It doesn't surprise me that the Russians would use the correct term of Angle of View regardless of language or the peculiarities of translation. Much of my online interactions with Russians over the years has been around the topic of photography, especially traditional analogue film based photography with view cameras and fine quality vintage lenses. When I sold off my view cameras, lenses and related equipment some years back, the Russians were the most enthusiastic buyers. From this I learned that for many Russians there is an appreciation and reverence for photography in a way that has been lost in many other countries to automated digital cameras where consumers no longer have to think about these principles and concepts.

I had an interesting experience checking out the Angle of View calculator link you posted. Using Google translate I was able to see an English language version of the calculator and play around with it. If I understand correctly, it uses the trigonometric calculations I mentioned earlier to function.

 

[Dashmellow]

The reason the difference between the terms AOV and FOV is meaningful for dash cam users is that AOV is an important lens specification used by optical professionals, photographers, cinematographers and film directors when selecting which lenses they use for their work. FOV on the other hand is basically a vague and inaccurate term that is not quantifiable becasue it is variable, as explained in my OP. Despite this, like many things in marketing it has somehow become the default term everyone uses.

The other day I even came across a video on YouTube where a skilled mathematician carefully explains how to calculate the trigonometric formula to determine "Field of View", except that he is actually explaining the equation for AOV - Angle of View although throughout the entire video he keeps using the term FOV instead of AOV (FOV uses a different equation to calculate). So even a skilled mathematician who clearly understands the concept involved is using the wrong terminology to describe what he is teaching.

There seem to be many incorrect terms and misconceptions in dash cam market that exist primarily due to marketing.

As consumer gadgets we see a lot of marketing hype and misinformation in the dash cam industry like FOV and complete nonsense like “7 glass lens” (a meaningless and intentionally misleading marketing hype term.)
"7 glass lens” and "7 Element All Glass Lens" was a marketing technique that as far as I am aware began with Jokiin from Street Guardian that spread to the rest of the industry. I call it the “More is Better” syndrome, although Jokiin certainly didn't invent this approach as it has been around a long time, he simply deployed it in the service of marketing and selling dash cameras. "It has 'more' lens 'elements' so therefore it must somehow be better".

“7 element lens "refers to the number of glass optical elements used in the M12 lenses used in many dash cams; at least according to Street Guardian. But the number of elements in an given lens has literally NOTHING to do with the quality or sharpness of the image it can create. For example, one of the finest, sharpest, most well corrected commercially successful lenses ever made was the 50mm ƒ/3.5 Leitz Elmar sold between 1925 and 1961 which had only four elements yet it would far exceed the performance of any of today’s so called "6 glass" dash camera lenses. The 50mm Elmar was the primary lens provided with the original Leica 35mm cameras.



But to make the Street Guardian marketing "more is better" hype even more egregious, the so called “7 element lens” being offered really has only 6 elements with the 7th "element" actually being nothing more than the IR-cut filter, falsely being claimed as an extra optical "lens element". But EVERY color digital camera on the market has an IR-cut filter which is merely a piece of specially coat flat glass that in many cameras is often mounted over the sensor, not directly on the lens as in dash cams. Characterizing a glass filter as a lens element for the sake of product marketing is intentionally misleading misinformation and in my view is an unethical practice.

Street Guardian SGCXPRO+




The dash cam industry is rife with this kind of misleading marketing and often the term FOV becomes part of this, again because it is not an actual specification that can be defined.

My hope is that one day we will see more accuracy, honesty and education of the camera buying public regarding how dash cams are marketed so that consumers can make intelligent decisions based on actual specifications like AOV, This way consumers can make informed, intelligent choices based on facts when they select a camera and lens combination similar to the way high end camera professionals do. The dash cam industry would be well served by more accurate information about camera specifications with less misleading sales hype.

As I've been saying in this thread, all of what I've described here contrasts sharply with how high end cameras and lenses are marketed. Professionals require factually accurate specifications when they make purchasing decisions for lenses so they can obtain products that suit their needs and expectations for their work.

Here's a good example from Hasselblad. Not only do they provide the Angle of View of all their lenses but they also provide the AOV specifications in degrees for every axis, diagonal, horizontal and vertical.