Focal ratio formula

The focal ratio formula is F=f/d, where f stands for focal ratio, f stands for lens focal length and d stands for lens aperture.

1. In optics, the focal length ratio (English F number, or F ratio, relative aperture, aperture value, etc. ) indicates the relationship between the focal length (mm) and the aperture diameter (mm) of the lens. Simply put, the focal ratio refers to the ratio of the focal length of the telescope to the aperture, which is the aperture value on the camera lens.

2. If the focal length is constant, the larger the telescope aperture, the smaller the focal ratio and the brighter the image. The focal length ratio is the ratio of the focal length to the aperture of a telescope. It is a dimensionless quantity to express the relationship between the focal length and aperture of a telescope, and it is also a parameter to measure the power of a telescope. The focal length ratio is determined by the focal length and aperture of the lens. The longer the focal length, the larger the aperture, the smaller the focal ratio and the stronger the optical power.

3. Conversely, the shorter the focal length, the smaller the aperture, the greater the focal ratio and the weaker the optical power. The focal ratio can also be understood as the relative aperture of the telescope. Relative aperture is the ratio of telescope focal length to transparent aperture, and its relationship with focal ratio is reciprocal, that is, relative aperture = 1/ focal ratio. The larger the relative aperture, the smaller the aperture, and vice versa.

The use methods and skills of the formula are as follows:

1. Determine the focal length and aperture of the telescope: Before using the focal ratio formula, it is necessary to determine the focal length and aperture of the telescope. Generally speaking, this information will be listed in the specifications or specifications of the telescope. Calculation of focal ratio: Divide the focal length of the telescope by the aperture to get the focal ratio.

2. Choose the appropriate focal ratio according to the observation requirements: different types of telescopes are required for different observation requirements, so you need to choose the appropriate focal ratio according to your own needs. For example, if you need to observe dark stars, you can choose a telescope with low focal ratio, and if you need to observe bright stars or take celestial photography, you can choose a telescope with high focal ratio.

3. Pay attention to the field of view of the telescope: When using the focal ratio formula, you also need to pay attention to the field of view of the telescope. Generally speaking, the larger the field of view of the telescope, the larger the sky area that can be observed, but it will also lead to poor imaging quality. Therefore, when choosing a telescope, you need to choose the appropriate field of view according to your own needs and budget.