Computes Field of View seen by camera and lens, both the dimensional size of the Field Of View seen at a specified distance, and also Angle Of View, for any sensor size (film or digital). Uses of course include computing dimensional field of view size at the subject distance. It can also compute the background size at the background distance (computed at the specified distance from camera). The Angle of View is independent of distance, and applies to this focal length on this size sensor, at any distance.
There is also a large table of angular Field of View (degrees) for many lens focal lengths and a few popular sensors lower on this page (or Option 1 or 3 shows more specific cases).
This calculation works when sensor size and focal length are known. These values may be difficult to determine for compact cameras and phones and camcorders, but DSLR values should be easily known. Some Field of View calculators assume only one default sensor size or ratio, but this one is general purpose, offering 3:2, 4:3, and 16:9 too. Or entering the sensor or film size can be any ratio.
The calculator is NOT for fisheye lenses (their view will be wider), and it is not for macro distances (at end below). Field accuracy will be better at a distance of at least several feet (say past 6 feet or 2 meters), because the lens focal length number changes with closer distance. The stated value of focal length applies to Infinity focus.
Enter Focal Length and Distance, select a sensor size in Option 1-4, then click Compute. Options 1-4 are four ways to specify sensor size. Then FOV is computed from focal length, distance, and sensor size. Or Options 5-8 are more special purpose.
Do NOT specify equivalent or effective focal length. Use the actual lens focal length with the actual sensor size. (You can specify crop factor as a way to compute actual sensor size, but that's a different subject.) The Exif reports actual real focal length.
Numbers only (a NaN result means input is Not A Number). Periods as decimal points are OK.
Please report ( Here ) any problems with the calculator, or with any aspect of this or any page. It will be appreciated, thank you.
Focal length is entered as millimeters, but distance units can be feet or meters, miles or cubits, your choice. Dimension results will be those same units. If the units are to be feet, then clicking the little Green button (by Distance, marked I for Inch) will assume feet, and will repeat Dimensions in feet ' and inches " format. You can click the Green button again to toggle this option off.
Angle of View (degrees) for a lens focal length and sensor is independent of subject distance, so if only that Angle goal, you can simply ignore the Distance and field dimension parts. Dimensions are calculated for the Distance, for that Angle.
Sensor size and focal length are all important to know. If unknown, sensor size can be computed from Crop Factor if known (see below). Exif should show focal lengths.
Select an Option, and click the Compute button (for all Option numbers).
Options 1-4 are four ways to specify sensor size.
Special Feature: In Option 3, the All Focal button will instead show Angular field of view of many focal lengths, used with this sensor size and aspect ratio. The crop factor (1, 1.5, 1.6, 2.7, etc) selected in Option 3 computes the sensor size. Or you can just use Option 1 directly.
Special Feature: In Option 4, the All Sensors button will instead show a summary of all sensors in the Option 4 list.
The biggest risk to accuracy is not actually knowing the specific sensor size, and not actually knowing the specific accurate focal length. DSLR cameras do better describing those specifications. Compacts and phones may be difficult to know (and Crop Factor might be your best tool).
Possibly the most usable general understanding to compare focal lengths (for a given sensor, and a medium or longer lens focal length, but not wide angles) is that the resulting image size is the simple ratio of the two focal lengths. A 400 mm lens will show an enlarged view 4x the subject size and 1/4 the field of view of a 100 mm lens (100/400 = 1/4). This is valid for "normal lenses" and longer focal lengths, but becomes not so true for wide angle lenses.
One example: Suppose you want a portrait to include a 2x3 foot subject area. You know you need to stand back six or eight feet for proper portrait perspective. What focal length is that field size going to require? And the background may be five feet farther back, how large does it have to be? This calculator can plan or verify your choice. If you want to see fractions of inches better, you can enter distance as inches (ten feet = 120 inches), but realistically, the accuracy (of the focal length) may not be up to fractions of an inch.
Determine Crop Factor: Field of View requires knowing focal length and sensor size. In some cases, focal length is in the Exif data. Sensor size might be found in the camera specs, but it can sometimes be difficult to know. Sensor size can be computed from Crop factor.
For example, the specification for a compact camera's zoom lens might say:
This spec says the zoom focal length is 4.5 to 81.0 mm. That is what the lens is. It also says that a 35 mm film camera (on its sensor size) would see the same field view with a 25-450 mm lens. If you are used to using 35 mm film, this is convenient to know. This says this cameras 4.5 mm lens is the equivalent view of a 25 mm lens on a 35mm film camera. That relation is what crop factor is, so it makes crop factor be 25 mm / 4.5 mm or 450 mm / 81 mm, both equal to 5.55 crop factor.
<song and dance> So Equivalent focal length is NOT what this lens does. The focal length of this lens is as specified, it only does what it does. Equivalent focal length only describes the lens that a 35 mm film camera would use to see the same field of view as this lens sees on this camera. If you are used to 35mm film lenses, this will be convenient information, to compare the expected field of view of this lens. But it does not affect what this lens does on this camera. Crop Factor is the degree that the smaller sensors reduce the field of view, as compared to the field of view of 35 mm film cameras used as a comparison standard.
IF you specify equivalent focal length in this calculator, then you also must only specify the 35mm film full frame 36x24 mm sensor size that it applies to. That will use 3:2 aspect ratio, but will otherwise work, but it seems roundabout.
Crop factor is also the ratio of the 35 mm film diagonal divided by this sensors diagonal. We know 35 mm size, so knowing crop factor can tell us sensor size. So computing sensor size will be as accurate as your data numbers. However, the focal length actually used in compacts is probably not known except at the extremes that the zoom spec mentions (and default power up zoom is probably some unknown intermediate point).
Smart phones don't zoom, but official specs are rare. Sensor size can be computed from crop factor, if known. Sources differ, and Apple specs don't say, but one estimate is that an iPhone 5 sensor size is 4.54 mm * 3.42 mm and crop factor 7.93x. If you can determine either sensor size or crop factor, the calculator above will compute the other. iPhone 5 Exif reports focal length of 4.2 mm.
Crop factor is often specified as a slightly rounded number. For example, the 35 mm film frame is 36 mm wide, and if the DX sensor is 23.5 mm width, then it is actually 36 mm/23.5 mm = 1.53 crop, but called 1.5x. But, the focal length number is also approximated anyway.
Entering exact sensor dimensions above would be the most precise. The camera manufacturers specify the equivalent 35 mm crop factor from the diagonal ratio to 35 mm film (because many of us are very familiar with 35 mm film, and crop factor tells us what view to expect now). We may not know sensor size or focal length on compacts, except at either end of the zoom range, but then we can determine crop factor, for example, if they specify their 6.1 mm lens is equivalent of 24 mm lens on a 35 mm camera, then obviously their crop factor is 24/6.1 = 3.93. And after the fact, the Exif (Manufacturers Data section) often shows the zoom focal length used for the picture (see a viewer that will show this).
HDTV 16:9 movies: Special considerations. The differences in the Aspect menu in Option 3 above is that DSLR and compacts take 3:2 or 4:3 photos, and their diagonal fits in the diameter of the lens circular view. Their HDTV movies possibly might be smaller than sensor width, but can't be larger (and are of course resampled to 1920x1080 or 1280x720 pixels). The 16:9 movies in still cameras are constrained within that still camera sensor size, limited to the same width. Whereas camcorders fit the full diagonal, not constrained by any 3:2 or 4:3 sensor width. Generally, if camcorders also take still pictures, those are 16:9 too.
In this image at right, the blue circle represents the diagonal of the image that the lens projects. 16:9 in camcorders is wider, but not if constrained within the more narrow frame sizes. I suppose there could be some exception, but camcorders should have a 16:9 sensor, and DSLR, compacts and phones typically have 4:3 or 2:3 camera sensors. Their 16:9 width will be the same as the 4:3 width, but then the height is less. Another page also describes this effect numerically.
Determine aspect ratio by dividing image width by the height (both in pixels), which is its aspect ratio. 3:2 divides as 1.5, 4:3 divides as 1.33, and 16:9 divides as 1.78. So if your movie mode takes still pictures of aspect 1.78, then it is probably a camcorder with a 16:9 chip.
Many photo cameras will use their full sensor width for their HD movie width (Nikon D7100, D600, D750 specify their movies are full sensor width) and that is assumed here. But for example, the D800/D810 use slightly less width (these D8xx manuals specify the sensor image area for FX HD movies is 32.8 x 18.4 mm FX, and DX HD is 23.4 x 13.2 mm). That is 35.9/32.8 = 91% of full width. An iPhone 5S (on a tripod) measures the movie field of view to be 91% less too. This field of view reduction could be computed by using effective Focal Length = 1/0.91 times longer (10% longer), OR a crop factor 1/0.91 times larger (10% larger).
But actually knowing the actual sensor size is the key.
Here's a chart of Angular Field of View (Width, Height, Diagonal, in degrees) for many lens focal lengths ("Lens mm") on popular sensor sizes and common aspect ratios. One example of the chart use might be to compare the width of view on two cameras.
The calculation is NOT for fisheye lenses (their view will be wider), and it is not for macro distances. Field accuracy will be better at a distance of at least several feet, because the lens focal length number changes with closer distance. The stated value of focal length applies to Infinity focus.
The top row marked WxH shows the sensor dimensions in mm, computed from the crop factor. The APS-C 1.61x and 1.53x crop numbers are realistically closer than the nominal 1.6x and 1.5x approximations we think of. Crop factor can be determined in the first calculator above. Also 16:9 image size can be limited to be no wider than camera 3:2 or 4:3 sensors (or left at full size for camcorders). See HD movies above.
There are many sizes of 4:3 sensors. Tiny sensors require very short focal length to achieve any usual field of view. Phones normally don't zoom, and we probably don't know focal length for compacts except at end extremes.
You can easily add another sensor into the chart (specify crop factor), which will replace the last sensor column (replaces the original default 2.73x crop initially in last column.) See Determine Crop Factor above.
The last sensor is really just a place holder for any other sensor you want to add there instead. (Refresh the page to restore the original sensor).
FWIW, the size of our full Moon appears near 0.5 degrees (its size varies slightly in its elliptical orbit, 0.49 to 0.558 degrees).
We can realize from this chart that generally, a 2x longer focal length often shows a view only half as wide. Or 4x is 1/4 as wide, etc. But due to the angle trig, this is not linear, meaning it is Not true of wide angles. I am arbitrarily suggesting that a horizontal view width of the "normal" lens, or longer, or roughly about 40 degrees horizontal or less, reasonably satisfies this, and then 2x focal length will be near half angle, about 20 degrees. This is true of full frame at about 50 mm, and true of APS-C sensors at about 30 mm. Very close if longer, and really, still "close enough" if a little wider, within a degree or two. It's another detail of crop factor. But it is true of longer lenses, that 2x focal length is about half the view width.
There are approximations in calculations. The math is precise, but the data is less so. Focal length is a little vague, as might be the precise sensor size. However, the results certainly are close enough to be very useful in any practical case. My experience is that the field is fairly accurate (at distances of at least a meter or two), assuming you actually know your parameters. Some problems are:
The Marked focal length of any lens is a rounded nominal number, like 50 or 60 mm. The actual can be a few percent different. Furthermore, the Marked focal length is only applicable to focus at infinity. Focal length necessarily increases when lens is extended forward to focus closer. Also zoom lenses can do other internal tricks with actual focal length (some zooms can be shorter when up close, instead of longer). Focal length will be less accurate at very close distances, and field of view becomes a little smaller. So macro distances are left out, but any error should be small if focused beyond one or two meters. You also have to measure your distance and field dimensions accurately too. And of course, we are only seeking a ballpark number anyway, we adjust small differences with our subject framing.
And a fisheye lens is a different animal, wider view than this formula predicts. A regular lens is rectilinear, meaning it shows straight lines as straight lines, not curved. A fisheye is rather unconcerned about this distortion, and can show a wider view, poorly purists might say, but very wide, and very possibly interesting.
Actual focal length can be determined by the magnification (Wikipedia). Or, the focal length (f), the distance from the front nodal point to the object to photograph (s1), and the distance from the rear nodal point to the image plane (s2) are related by this Thin Lens equation:
If OK with a little geometry and algebra, you can see the derivation of this classic Thin Lens Equation at the Khan Academy.
In this equation, we can see that if the subject at s1 is at infinity, then 1/s1 is zero, so then s2 = f. This says that the marked focal length applies when focused at infinity.
Also if at 1:1 magnification, then s1 = s2, saying that the working macro distance in front of the lens is equal to the (extended at 1:1) focal length of the lens.
The field of view math is basic trigonometry. The focal length measures from lens node to sensor. We compute the right triangle on center line, of half the sensor dimension, so the half lens angle = arctan (sensor dimension / (2 * focal length)). The Subject distance is in front of lens node, with same opposite angle. Field dimension = 2 * distance * tan (center line half angle). The problem is that focal length f becomes longer when focused at close distances (but the opposite can be true of a few zoom lenses). That becomes an insignificant field of view difference at normal distances, 1 meter or more.
Multi-element camera lenses are "thick" and more complex. We are not told where the nodes are designed, normally inside the lens somewhere, but some are outside. For telephoto lenses, the rear node (focal length from sensor plane) is in front of the front lens surface. The designer's term telephoto is about the reposition of the nodal point so that the physical lens is NOT longer than its focal length. Yet, this rear node is generally behind the rear lens surface of a wide angle lens (lens moved well forward to provide room to allow the larger SLR mirror to rise... 12 mm lens, 24 mm mirror, etc). This nodal difference is only a few inches, but it affects where the focal length is measured. And it shifts a bit as the lens is focused closer. Repeating, the focal length marked on the lens is specified for focus at infinity.
The Subject distance S is measured to the sensor focal plane (it is the "focus distance"), where we see a symbol like Φ marked on the top of the camera (near rear of top LCD). The line across the circle indicates the location of the sensor plane (for focus measurements). However, the Thin Lens Equation uses the distance d in front of lens. This is why we often see in equations: (S - f) used for d.
For Macro, computing magnification is more convenient than focal length (since we don't really know focal length at macro extension). Focal length and subject distance determine Magnification, which is the ratio of size of image to size of actual subject. Or the ratio of size of sensor to the size of the remote field. We could compute for magnification here, but we likely don't know new focal length at that close magnification. Just using magnification has more significance up closer (easier for macro), which is where our knowledge of the actual focal length is weakest. We could measure the field to compute the actual magnification. However Magnification is simply:
m = s2/s1. Or m = f/d. Or m = f/(S-f).
So from this, we know macro field of view is simply the sensor dimensions, divided by the magnification. Let's say it this way:
1:1 macro, the focal length f is same as the distance d in front of lens (each with its own node).
1:1 macro (magnification 1), the field of view is exactly the same size as the sensor.
1:2 macro (magnification 0.5), the field of view is twice the size of the sensor.
1:4 macro (magnification 0.25), the field of view is four times the size of the sensor.
This is true of any focal length for any lens (or method) that can achieve the magnification. Focal length and subject distance are obviously the factors determining magnification (it is still about them), but magnification ratio is simply easier work for macro.
The easiest method to determine field of view for macro is to simply put a mm ruler in the field. If a 24 mm sensor width sees 32 mm of ruler, then that is the field of view, and the magnification is 24/32 = 0.75 (this scale of magnification is 1 at 1:1, and is 0 at infinity).
The definition of macro 1:1 magnification is that the focal length and subject distance are equal (distances in front of and behind the lens nodes are necessarily equal, creating 1:1 magnification). In this Thin Lens Equation, if s1 and s2 are equal, the formula is then 2/s1 = 1/f, or 2f = s1. So lens extension to 2f gives 1:1. And since f/stop number = f / diameter, then if 2f, then f/stop number is 2x too, which a double f/stop number is 2 stops change, which is the aperture loss at 1:1. We know those things, this is just why.
But the point here, if f is actually 2f at 1:1 macro, the field of view changes with it. None of the FOV calculators are for macro situations (too close, magnification is instead the rule there). Field of View calculators expect subject distance to be at least a meter or two, reducing the focal length error to be insignificant.