Zooming your camera's lens for telephoto shots increases the focal length. With no change in the lens area, this will a. increase the \(\mathrm{f}\) -ratio and increase the lens speed. b. decrease the f-ratio and decrease the lens speed. c. increase the f-ratio and decrease the lens speed. d. not change the f-ratio or the lens speed.

The f-ratio, often denoted as f-number or f-stop, is a crucial concept in photography that impacts exposure and depth of field. It is expressed as a ratio of the lens's focal length to the diameter of its entrance pupil, which is essentially the lens aperture.

In simpler terms, the f-ratio determines how much light is allowed to pass through the lens and reach the camera's sensor. It's calculated using the formula \( f\text{-}ratio = \frac{\text{focal length}}{\text{diameter of entrance pupil}} \). When you adjust your lens to zoom in for a telephoto shot, you are increasing the focal length. Assuming that the diameter of the lens opening (aperture) remains unchanged, this results in a larger f-ratio number, indicating a proportionally smaller aperture.

It's worth noting that the f-ratio is inversely related to the amount of light that enters the lens: a higher f-ratio means a smaller aperture and less light, while a lower f-ratio means a larger aperture and more light. Photographers manipulate the f-ratio to achieve desired lighting effects and control depth of field in their images.

Lens speed is an essential factor in photography that refers to the ability of a lens to capture light. The term 'fast' or 'slow' when relating to lens speed is indicative of the amount of light a lens can gather and transmit to the sensor. Faster lenses have larger maximum apertures, denoted by smaller f-ratio numbers, which allow more light to pass through them enabling quicker shutter speeds to freeze motion or shoot in low-light conditions without a flash.

A fast lens is highly advantageous for photographers who shoot in varying lighting situations, particularly those requiring natural light. Conversely, a slow lens, with a larger f-ratio, admits less light and may necessitate the use of longer shutter speeds or higher ISO settings, increasing the potential for image blur or noise. Therefore, understanding the relationship between the f-ratio and lens speed is key to selecting the right lens for the photographic conditions and subjects at hand.

It is a common misunderstanding that the physical speed of the lens elements themselves changes. However, the term 'speed' is metaphorical and concerns the exposure time, related to how quickly the camera can achieve correct exposure given the amount of light the lens lets in.

Telephoto lenses are a type of camera lens designed for photographing distant subjects. They have a long focal length, typically above 70mm, which enables them to magnify the subject and make it appear closer to the camera than it actually is. This feature is essential for sports, wildlife photography, and any situation where the photographer cannot get close to the subject.

One distinctive trait of telephoto lenses is their ability to compress the scene, making objects appear closer together than they do with a standard lens. This effect can be creatively used to achieve a shallower depth of field, isolating the subject from the background and creating a strong sense of presence.

However, telephoto lenses often come with larger f-ratio numbers, meaning they can be slower and require more light to achieve the same exposure as lenses with wider apertures. When zooming in, the f-ratio increases, making the lens slower, which relates back to the initial exercise that states zooming the lens increases the focal length, thereby increasing the f-ratio and reducing the lens speed. This is crucial to remember when managing shutter speed and ISO to maintain image sharpness in various lighting conditions.