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\(\cdot\) Camera \(A\) has a lens with an aperture diameter of 8.00 \(\mathrm{mm}\) . It photographs an object, using the correct exposure time of \(\frac{1}{30}\) s. What exposure time should be used with camera \(\mathrm{B}\) in photographing the same object with the same film if camera \(B\) has a lens with an aperture diameter of 23.1 \(\mathrm{mm}\) ?

Short Answer

Expert verified
Camera B should use an exposure time of approximately 1/250 seconds.

Step by step solution

01

Understand the Problem

We need to determine the correct exposure time for Camera B, given the exposure time for Camera A and the apertures of both cameras. The exposure time is influenced by the amount of light entering through the aperture.
02

Use the Aperture Formula

The aperture affects the exposure time according to the formula \( t_2 = t_1 \left( \frac{d_1}{d_2} \right)^2 \), where \( t_1 \) and \( t_2 \) are the exposure times for cameras A and B, respectively, and \( d_1 \) and \( d_2 \) are the aperture diameters.
03

Plug in Known Values

We know \( t_1 = \frac{1}{30} \) s, \( d_1 = 8.00 \) mm, \( d_2 = 23.1 \) mm. Substituting these into the formula, we get: \[ t_2 = \frac{1}{30} \left( \frac{8.00}{23.1} \right)^2 \]
04

Calculate the Ratio

First, calculate the ratio \( \frac{8.00}{23.1} \). This gives: \( 0.346 \). Now square the ratio: \( 0.346^2 = 0.1197 \).
05

Calculate the Exposure Time for Camera B

Now multiply the squared ratio by the exposure time of Camera A: \( t_2 = \frac{1}{30} \times 0.1197 \approx 0.004 \) seconds. Thus, the exposure time for Camera B should be approximately \( 1/250 \) seconds.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Camera Exposure Calculation
Calculating the correct exposure for a photograph is key to getting a well-exposed image. Exposure is the amount of light that reaches the camera's sensor, which is influenced by three factors: aperture, shutter speed, and ISO. In this context, we focus on the first two—aperture and shutter speed.
The formula used to calculate the required exposure time for different apertures is:
  • \( t_2 = t_1 \left( \frac{d_1}{d_2} \right)^2 \)
Here, \( t_1 \) and \( t_2 \) represent the exposure times for two different scenarios, typically involving two lenses with different aperture diameters, \( d_1 \) and \( d_2 \). The exposure time is shortened or lengthened based on how much the aperture diameter changes.
Hence, understanding and applying the formula is crucial when switching lenses or cameras with different apertures. It ensures that the photographed object remains properly exposed, preventing it from being too bright or too dark.
Aperture Diameter
Aperture diameter is one of the most critical components in photography, especially concerning exposure. It affects how much light enters the lens, which directly influences the detail and brightness of a photograph.
In this problem, Camera A and Camera B have different aperture diameters, 8.00 mm and 23.1 mm, respectively. The larger the aperture diameter, the more light hits the sensor. This might be likened to opening a larger window in a dark room, allowing more sunlight to fill the room.
Since Camera B has a larger aperture, it gathers more light than Camera A for the same amount of time. Consequently, its exposure time needs to be adjusted to compensate for this increased light intake. This adjustment helps in achieving the perfect balance between light and the photograph's final look.
  • Smaller apertures require longer exposure times
  • Larger apertures can work with shorter exposure times
Being aware of these aspects allows photographers to make informed decisions and achieve desired photographic effects irrespective of changing lighting conditions.
Photography in Physics
Photography beautifully intersects with physics when capturing light and creating images. Understanding these principles allows photographers to manipulate elements like light and time effectively.
Physics demonstrates how the interaction between camera settings such as aperture and exposure time can affect a photograph's outcome. The aperture operates much like a pupil in the human eye, expanding and contracting to regulate light intake.
An understanding of exposure and aperture in a physical context translates into practical know-how in photography. Utilizing concepts like the inverse square law, physics explains why doubling the distance of a light source decreases its intensity to a quarter, which parallels the idea of aperture and exposure manipulation in photography.
Emphasizing these scientific principles bridges the gap between formulating the exposure calculation and its practical application, ensuring photographers of all experience levels can produce well-balanced images.

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Most popular questions from this chapter

\(\bullet\) Galileo's telescopes, I. While Galileo did not invent the telescope, he was the first known person to use it astronomically, beginning around \(1609 .\) Five of his original lenses have survived (although he did work with others). Two of these have focal lengths of 1710 \(\mathrm{mm}\) and 980 \(\mathrm{mm}\) . (a) For greatest magnification, which of these two lenses should be the eye- piece and which the objective? How long would this telescope be between the two lenses? (b) What is the greatest angular magnification that Galileo could have obtained with these lenses? (Note: Galileo actually obtained magnifications up to about \(30 \times\) but by using a diverging lens as the eye- piece.) (c) The Moon subtends an angle of \(\frac{10}{2}\) when viewed with the naked eye. What angle would it subtend when viewed through this telescope (assuming that all of it could be seen)?

.. In a museum devoted to the history of photography, you are setting up a projection system to view some historical 4.0 inch \(\times 5.0\) inch color slides. Your screen is 6.0 \(\mathrm{m}\) from the projector lens, and you want the image to be 4.0 ft \(\times 5.0\) ft on the screen. (a) What focal-length lens do you need? (b) How far from the lens should you put the slide?

\(\bullet\) Resolution of a microscope. The image formed by a microscope objective with a focal length of 5.00 \(\mathrm{mm}\) is 160 \(\mathrm{mm}\) from its second focal point. The eyepiece has a focal length of 26.0 \(\mathrm{mm}\) . (a) What is the angular magnification of the microscope? (b) The unaided eye can distinguish two points at its near point as separate if they are about 0.10 \(\mathrm{mm}\) apart. What is the minimum separation that can be resolved with this microscope?

\(\cdot\) The focal length of an \(f / 4\) camera lens is 300 \(\mathrm{mm}\) . (a) What is the aperture diameter of the lens? (b) If the correct exposure of a certain scene is \(\frac{1}{250}\) s at \(f / 4,\) what is the correct exposure at \(f / 8 ?\)

. A 135 mm telephoto lens for a 35 mm camera has \(f\) -stops that range from \(f / 2.8\) to \(f / 22\) . (a) What are the smallest and largest aperture diameters for this lens? What is the diameter at \(f / 11 ?\) (b) If a 50 \(\mathrm{mm}\) lens had the same \(f-\) stops as the telephoto lens, what would be the smallest and largest aperture diameters for that lens? (c) At a given shutter speed, what is the ratio of the greatest to the smallest light intensity of the film image? (d) If the shutter speed for correct exposure at \(f / 22\) is 1\(/ 30\) s, what shutter speed is needed at \(f / 2.8 ?\)

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