Chapter 35: Q. 8 (page 1016)
To focus parallel light rays to the smallest possible spot, should you use a lens with a small f-number or a large f-number? Explain.
smaller f-numbered lens
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Modern microscopes are more likely to use a camera than human viewing. This is accomplished by replacing the eyepiece in Figure 35.14 with a photo-ocular that focuses the image of the objective to a real image on the sensor of a digital camera. A typical sensor is 22.5 mm wide and consists of 5625 4.0@mm@ wide pixels. Suppose a microscopist pairs a 40* objective with a 2.5* photo-ocular.
a. What is the field of view? That is, what width on the microscope stage, in mm, fills the sensor?
b. The photo of a cell is 120 pixels in diameter. What is the cellโs actual diameter, in mm?
A -diameter microscope objective has a focal length of . What object distance gives a lateral magnification of ?
A camera has a circular aperture immediately behind the lens. Reducing the aperture diameter to half its initial value will
A. Make the image blurry.
B. Cut off the outer half of the image and leave the inner half unchanged.
C. Make the image less bright.
D. All the above.
Explain your choice.
Youโve been asked to build a telescope from a magnifying lens and a magnifying lens.
a. What is the maximum magnification you can achieve?
b. Which lens should be used as the objective? Explain.
c. What will be the length of your telescope?
The resolution of a digital cameras is limited by two factors diffraction by the lens, a limit of any optical system, and the fact that the sensor is divided into discrete pixels. consirer a typical point-and--shoot camera that has a lens and a sensor with pixels.
(a) . First, assume an ideal, diffractionless lens, at a distance of what is the smallest distance, in between two point sources of light that the camera can barely resolve? in answering this question, consider what has to happen on the sensor to show two image points rather than one you can use
(b) . You can achieve the pixel-limied resolution of part a only if the diffraction which of each image point no greater than the diffraction width of image point is no greater than pixel in diameter. for what lens diameter is the minimum spot size equal to the width of a pixel ? use for the wavelength of light.
(c). what is the of the lens for the diameter you found in part b? your answer is a quite realistic value of the at which a camera transitions from being pixel limited to being diffraction limited for smaller than this (larger-diameter apertures), the resolution is limited by the pixel size and does not change as you change the apertures. for larger than this (smaller-diameter apertures). the resolution is limited by diffraction and it gets worse as you "stop down" to smaller apertures.
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