Focal length is something that we talk about constantly as we discuss different lenses and styles of photography in our weekly free podcasts. It can be a bit confusing as a beginner to understand focal length because there are a few twists and complexities, but I'll do my best to explain it in 5 minutes or less. Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. Join them; it only takes a minute. Longer focal length will give a shorter DoF for a given distance. Shorter focal length will give you a wider background. For full body portraits, though, neither a 50mm or 85mm is probably.
The primary measurement of a lens is its focal length. The focal length of a lens, expressed in millimeters, is the distance from the lens’s optical center (or nodal point) to the image plane in the camera (often illustrated by a 'Φ' on the top plate of a camera body) when the lens is focused at. The image plane in the camera is where you will find your digital sensor or film plate. If you are an optical engineer, this is important stuff. For the photographer, however, we do not need to know about nodal points or why the 200mm lens in our closet is only 193mm long, to make great photos. 'A standard lens will provide the most normal perspective'The use of the term perspective here is unfortunate.
The only thing that can alter perspective is moving the position of the camera. A wide angle lens does not distort geometric perspective. That's what people look like up close.
Take that photo of your friend and print it big. Now stand close enough so that it fills the same angle of view as the lens provided to the sensor. Nothing will be distorted. Check out the skull in Holbein's The Ambassadors. It looks undistorted from a certain angle, as would the corners of a wide angle shot when presented to a viewer in such a way as to match the FOV of the original shot.So your use of the term 'distort' is misleading as well. It runs the risk of being conflated with barrel and pincushion distortion - genuine distortions that are indeed a property of the lens.Focal length determines angle of viewDistance of subject from lens determines perspectiveSomeone standing 2 feet from you will be just as distorted at 200mm focal length as at 16mm.
You'll just see a narrower slice of the scene in front of you. Maybe a nostril! Hey Mike,Thanks for your comments!I wrote this article as an introduction for photographers new to the world of photography. Therefore, I chose not to dive too deeply into the technical.When capturing a photograph of an object at very close range with a wide angle lens, you do experience distortion. This distortion is not caused by a rectilinear lens is suddenly distorting the view—recilinear is recilinear— the distortion happens because of the more oblique angles that the light is entering the lens. The closer the subject is to the lens, the more variation there is in the angles of entry of the light rays from an object.
Subject-lens distance is the cause.not really a distorting lens. For the beginner, this is difficult to describe without encouraging the audience to study the inside of their eyelids instead of a lens diagram.Remember, when you are comparing a camera lens/photograph to looking at someone up close with your eyes, you are still viewing them through a wide angle lens.your own wide-angle lens—the eyeball.
Your eye experiences that same larger delta between light rays at the edges and the center of the 'frame.' You would see it more if the eye had a closer minimum focus distance.Check out these two articles on perspective and distortion:Your statements are correct, Mike, however, I chose to stay out of the weeds in this basic article.Thanks for stopping by and commenting! Different digital cameras have different-sized sensors. This causes an effective change in the field of view of the camera, but not in the focal length of a given lens.This is exactly the answer I was looking for. Just to put it another way, this means if I have a shot taken on a 50mm prime, with a 1.6 crop factor sensor, it is still correct to say the lens' focal length for the image was 50mm, rather than 80mm?
It's the field of view that has changed, effectively cropping the image, although it might be convenient to say the produced image 'looks like it's been shot with an 80mm lens and 35mm sensor.' Thanks for the article!