What's the difference between telephoto and optical zoom?

1, with different concepts. Optical zoom means that the actual focal length of the lens itself can be changed, that is, the focal length of the lens can be changed. Telefocus means that the lens has a long focal length.

2. The specific characteristics are different. The zoom lens can only reach the maximum allowable focal length through optical zoom. Usually a large zoom lens is a telephoto lens.

3. The structure is different. Telefocus is only a long focal length, but the focal length is fixed. Optical zoom can change the focal length and the viewing angle in a certain range.

Extended data:

When using a long focal length lens, the following points should be noted:

1. Use a high-speed shutter. Because the telephoto lens is large and heavy, it is not easy to hold it steady when shooting. In addition, the magnification of telephoto lens is large, the subject moves or the camera shakes slightly, and the image blur degree increases accordingly, so a higher shutter speed must be adopted.

2. Choose high-speed photographic film. Because the maximum aperture of telephoto lens is small, in order to prevent camera instability, it is often necessary to use a higher shutter speed to shoot. ISO 100 medium-speed photographic film is difficult to meet the exposure requirements under high-speed shutter, so it is best to use high-speed film when shooting with telephoto lens.

3. Increase the exposure appropriately. Here mainly refers to the telephoto lens of more than 200mm, because its long focal length, long lens body and multi-lens weaken the intensity of light reaching the negative, so it is necessary to increase exposure to make up for the loss of light. For lenses with a focal length of 200-400mm, half exposure should be increased, and for ultra-telephoto lenses with a focal length greater than 400mm, one exposure should be increased. The camera used for TTL metering is not in this list.

4. Add a filter. When a telephoto lens shoots a distant view, it is easy to produce gray phenomenon and the scenery is not clear and bright. This is due to the interference of ultraviolet rays and the reflection of dust and air medium, which leads to low contrast, blurred boundary and poor definition of the image. Therefore, it is necessary to install polarizers and ultraviolet filters to eliminate the influence of ultraviolet light and reflection and improve the contrast and clarity of photos.

5. Give full play to the stability function of tripod. There are three advantages to using a tripod when shooting with a telephoto lens: first, using a stable tripod and releasing the shutter with the help of a cable releaser can effectively prevent the weak vibration of the camera and ensure the clarity of the negative image; Second, it is beneficial for the camera to use a slower shutter speed and narrow the aperture; Third, you can focus and view more accurately.

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