Jills camera can photograph objects sharply 30 cm away but n

Jill\'s camera can photograph objects sharply 30 cm away but not closer. Find the focal length of the Jill\'s lens if the maximum distance allowed between the lens and the film plane is 130 mm?
________________ mm
How far in front of the film should the lens be if the object to be photographed is at the following distances from the lens?

(a) 12.8 m away
__________ mm
(b) 4.6 m away
__________ mm
(c) 1.1 m away
__________ mm

Solution

1.

From Thin lens formula

1/f =1/d_i+1/d_o

1/f = 1/130 +1/300

f=90.7 mm

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a)

For d_o=12.8 m =12800 mm

=>1/90.7 =1/d_i + 1/12800

d_i=91.35 mm

b)

For d_o=4.6 m =4600 mm

=>1/90.7 =1/d_i  + 1/4600

d_i=92.52 mm

c)

For d_o=1.1 m=1100 mm

=>1/90.7 =1/d_i + 1/1100

d_i=98.85 mm