To calculate the focal length, you will need to know the object distance (distance between the object and the lens), the image distance (distance between the lens and the image), and the object size. Once you have this information, you can use the formula: focal length = (object distance * image distance) / object size.
Reducing the viewing distance to 25cm allows for a clearer and more detailed view of the object. It also helps reduce eye strain and fatigue.
No, the focal length of the lens is directly related to the viewing distance. You will need to use a lens with a specific focal length to achieve a viewing distance of 25cm.
Other factors to consider include the type of lens (e.g. convex, concave), the aperture size, and the distance between the lens and the image sensor (for digital cameras).
Yes, this formula can be used to calculate the focal length for any desired viewing distance. Simply replace the 25cm with your desired viewing distance in the formula.