Do you have a bird-watching mirror with an equivalent focal length of 75 times? Is the equivalent focal length of 50x75 of 3750mm camera equal to 3750mm?

No, the equivalent focal length of 75 times bird-watching mirror is not equal to 3750 mm, and the focal length is calculated according to the actual lens focal length and the sensor size of the camera.

In photography, focal length refers to the distance between lens and imaging plane (sensor or film). The longer the focal length, the more obvious the magnification effect of the lens and the narrower the field of view.

The focal length of a bird-watching mirror is usually expressed in multiples, such as 75 times that of a bird-watching mirror. This multiple refers to the magnification of the viewing angle of the bird-watching mirror relative to the visual angle of the naked eye. It does not directly correspond to the actual focal length of the lens.

For example, if the actual focal length of a 75x bird-watching mirror is 50mm, its equivalent focal length will depend on the sensor size of the camera using it. If the sensor of the camera is Quan Huafu (35mm), the equivalent focal length is 50mm. But if the sensor of the camera is APS-C size, the equivalent focal length will be larger, because the sensor of APS-C size is smaller than Quan Huafu.

Therefore, it is necessary to consider the actual focal length and the sensor size of the camera to determine the equivalent focal length of the bird-watching mirror. Simply multiplying the multiple by the actual focal length is inaccurate.