Variation occurs in a formula from photography. In the formula L=(25 F^2)/(s t) the luminance, L

step 1 number 46 it's given the relation between l is equal to 25 f squared over f squared over st so i

Variation occurs in a formula from photography. In the...

Variation occurs in a formula from photography. In the formula $$L=\frac{25 F^{2}}{s t}$$ the luminance, $L,$ varies directly as the square of the F-stop, $F,$ and inversely as the product of the film ASA number, $s$, and the shutter speed, $t$ (a) What would an appropriate F-stop be for 200 ASA film and a shutter speed of $\frac{1}{250}$ sec when 500 footcandles of light are available? (b) If 125 footcandles of light are available and an $\mathbf{F}$ -stop of 2 is used with $200 \mathrm{ASA}$ film, what shutter speed should be used? (IMAGE CAN NOT COPY)

Variation occurs in a formula from photography. In the formula
$$L=\frac{25 F^{2}}{s t}$$
the luminance, $L,$ varies directly as the square of the F-stop, $F,$ and inversely as the product of the film ASA number, $s$, and the shutter speed, $t$
(a) What would an appropriate F-stop be for 200 ASA film and a shutter speed of $\frac{1}{250}$ sec when 500 footcandles of light are available?
(b) If 125 footcandles of light are available and an $\mathbf{F}$ -stop of 2 is used with $200 \mathrm{ASA}$ film, what shutter speed should be used?
(IMAGE CAN NOT COPY)

Key Concepts

Direct and Inverse Variation

This concept refers to the relationship between variables where one variable increases or decreases in direct proportion to another, and inversely in relation to a different variable. In mathematical formulas, direct variation means that as one factor increases, the other also increases by a constant multiple, whereas inverse variation means that as one factor increases, the other decreases, also by a constant factor. This is fundamental in understanding how changes to one parameter affect another in proportional relationships.

F-stop (Aperture) in Photography

The F-stop is a measure of the aperture size of a camera lens and plays a crucial role in controlling the amount of light that enters the camera. It is represented as a ratio and its value affects exposure; a smaller F-stop number corresponds to a wider aperture and more light, while a larger F-stop indicates a smaller aperture and less light. Understanding the F-stop is essential because its influence on exposure is quadratic, meaning changes in F-stop disproportionately affect the amount of light entering the camera.

Film Speed (ASA/ISO)

Film speed, indicated by ASA or ISO ratings, represents the sensitivity of the film or sensor to light. A higher film speed means greater sensitivity, enabling photography in lower light conditions but often at the expense of increased grain or noise. Knowing the film speed is important in calculating exposure, as it inversely affects the amount of light required for proper exposure.

Shutter Speed

Shutter speed is the length of time the camera's shutter remains open to expose the film or sensor to light. It is a critical component of the exposure triangle and directly affects the exposure of an image. Faster shutter speeds reduce the exposure time, capturing less light and often freezing motion, whereas slower speeds allow more light in but can result in motion blur. Its role is inversely proportional to the total light captured under constant lighting conditions.

Photographic Exposure

Photographic exposure is the overall amount of light that reaches the film or sensor, and it is determined by the interplay of the aperture (F-stop), shutter speed, and film speed (ASA/ISO). This concept is central to capturing the desired brightness and contrast in an image. Understanding how these three variables interact, as well as the principles of direct and inverse variation, is key to mastering exposure in photography.

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