Update : Saturday, February 18, 2012
Focal length determines the distance between the sensor and the point where the light rays are beginning to converge in the lens, also known as the optical center of the lens. Should know that the focal length on a digital camera is not the same as a film camera.
manufacturers always indicate the focus on objectives, as if you were using a film camera. This does not mean that the figures are wrong, it means that it is the actual focal length of the lens. Devices Digital have what is called a conversion coefficient that is not the same depending on digital devices and manufacturers. should not believe that this is not reality, this is an equivalence which do result in .
| Coefficient of conversion (example) | |||
|---|---|---|---|
| Device | Coefficient | Focal Target | Result Focal digital |
| Olympus E-3 | x2 | 70-200mm | 140-400mm |
| Canon 5D MkII | x1 | 70-200mm | |
| Canon D60 | x1.6 | 112-320mm | |
| Nikon D90 | x1,5 | 105-300mm | |
| Nikon D700 | x1 | 70-200mm | |
The focus will also define the angle of the shot. A Wide will not have the same angle of view than a telephoto lens. Viewing angle not change the perspective you be at an angle of 106 ° or 62 ° angle. only the distance will change your perspective. Do not think, by changing your focus, you'll have better leak points.
The photos you take will be completely different between a wide angle and zoom. With the wide-angle, you'll have a much broader vision of the world, whereas with a zoom, you will restrict vision an object or person away.
| Focal | Angle |
|---|---|
| 8mm | 180° |
| 14mm | 106° |
| 21mm | 92° |
| 24mm | 84° |
| 28mm | 74° |
| 35mm | 62° |
| 50mm | 36° |
| 85mm | 28° |
| 105mm | 23° |
| 135mm | 18° |
| 200mm | 12° |
| 300mm | 8° |
| 400mm | 6° |
| 600mm | 4° |
| 1200mm | 2° |
Taken with a Canon 5D Mk II and a Canon 70-200mm (ISO400 - f/3.2 - 1/2500)