Sometimes, they ask me what distance will be to the subject, if you photograph on a particular lens. In this article, I derived a simple calculation formula.
For calculations, I used a full-format camera with a physical sensor size of 36 X 24 mm.
I recommend reading the text under the images.
The viewing angle can be found in brochures, instructions or on the official websites of the lens manufacturer. But there is one small nuance, which for some reason few people take into account - the angle of view of the lens is indicated for the diagonal of the frame.
I work as a photographer and do not shoot “diagonal shots” at all (to take a shot with a diagonal fill of the frame), and therefore this data gives me only an approximate idea of the angle of view when shooting in normal portrait (vertical camera orientation) or landscape (horizontal camera orientation) mode ...
Output: the physical size of the matrix w * h and the focal length of the lens f.
Search for: formula for calculating the viewing angle diagonally, vertically, horizontally. Check the found Beta angle for f = 50mm.
Thus, the data taken from the official website (47 °) and verification (46,79 °) are the same.
Now let's find the angle of view horizontally (Xi) and vertically (Tau):
It turns out that if we shoot a portrait at a 50 mm focal length (vertical position of the camera), then the viewing angle at which we will need to enter the model will be only 40 degrees.
Now find formula for calculating the distance L, with which we will need to shoot so that an object with the given dimensions fits in the frame H.
Thus, if we shoot a model with a height of 180 cm on a full-frame camera with a lens that has a 50 mm focal length, then in order for the heels and the crown of the head to get into the frame with the vertical orientation of the camera, we will need to move back 2.5 meters, horizontally, to fit the entire model into the frame, you will need to step back 3.75 meters.
To be more precise, 5 cm of the focal length (or any other number of the focal length) from the focus plane to the plane of the matrix should be added to these numbers, because the distance is calculated from the object to the focal plane. And you also need to take into account the effect of changing the viewing angle of the lens at different focusing distances, because the same fifty dollars has the declared 47 ° only when focusing on infinity, more about this here.
If we shoot the same model for the same fifty dollars with the horizontal orientation of the camera, but already on the Nikon DX camera (Kf = 1.5), then we will need to move 5,6 meters. And if you take into account that in addition to the model itself, you still need to capture a bit of space from below and from above, then by fifty dollars it will be necessary to retreat by 7 meters.
To use the count for cropped cameras, use the formulas to specify the width w and height h for your camera. For Nikon DX cameras: w = 23.5 mm, h = 15.6 mm. The focal length f should be taken as indicated on the lens without any conversion. Basic formulas are highlighted. If you cannot find the value of w and h in the instruction, then usually w = 36 / Kf, h = 24 / Kf, where Kf is the value crop factor cameras.
It is very simple to find out the focusing distance to the subject from the already taken photo. To do this, just check EXIF photo using http://regex.info/exif.cgi (The site supports any photo format)
Thank you for attention. Arkady Shapoval.