|If you’ve ever photographed a building from street level looking upwards with a wide angle lens, then you have no doubt seen the effect. The wide angle distorts the building and bends the vertical lines. This is called barrel distortion.
Optical zooms and Focal length
50mm – standard field of view equal to what we see with our eyes
This is based on using film or a full frame sensor. The point at which the lens becomes wide angle will vary if using a cropped sensor.
A cropped sensor will be different and the effective wide angle threshold will depend on the crop factor. For example, with an APS sensor that has a crop factor of 1.3x, the wide angle threshold is 38mm
How to work it out: (50 /1.3 = 38) so anything below 38mm is wide angle, and anything above is telephoto.
For long focal lengths, the longer the focal length, the narrower the angle of light, and thus the narrower the field of view.
If you look at the diagram above you can see how the narrower angle of view has essentially cropped away a part of the scene you are seeing through the lens. Think of it as cropping part of the photo away.
Conversely, a wide angle effectively stretches the angle of light, and thus the image, and allows a wider view than the normal 50mm will allow. Just like a zoom or telephoto allows you get closer without actually moving further forward, a wide angle allows you get further away without actually moving further back. This can be useful when you don’t have room to move back. But again, this comes at a price: distortion
How much distortion you get will depend on the angle at which you shoot:
Shoot level and straight: When you do this you will minimise the warping effect on objects in your image with straight lines.
How to correct lens distortion when using a wide angle – A video tutorial