Homework Help

An 80 mm focal-length lens is used to focus an image for a camera, a) how far is the...

user profile pic

lkehoe | Valedictorian

Posted April 27, 2013 at 8:49 PM via web

dislike 1 like

An 80 mm focal-length lens is used to focus an image for a camera, a) how far is the image from the lens if the object to be photographed is 10 m away? b)  If the object is 3.0 m away? c) If the object is 50 cm away? D)  If the maximum distance from the lens to the image is 120 mm, what is the closest object on which this lens could focus?

2 Answers | Add Yours

user profile pic

pramodpandey | College Teacher | Valedictorian

Posted April 28, 2013 at 4:33 AM (Answer #1)

dislike 2 like

In Camera  we use convex lense.

for convex lense as convention  u is (-),vand f are (+)

and lense formula is

1/v-1/u=1/f

a.   f=80mm=.08m

     u= 10 m

Thus `1/v=1/.08+1/10`

`=1008/80`

`1/v=1008/80`

`v=80/1008`

`=.079m `  behind the lense.

b. same u= 3m

`1/v=1/.08+1/3`

`1/v=308/24`

`v=.078m `  behind the lense

C.u=50cm=.5m

`1/v=1/.08+1/.5`

`1/v=116/8`

`v=8/116x^(m+n)`

D. v=120 mm

v=.12m

1/.12=1/.08+1/u

100/12-100/8=1/u

-400/96=1/u

u=-96/400

=-.24 m

Ans.

 

 

user profile pic

lkehoe | Valedictorian

Posted May 6, 2013 at 7:47 PM (Answer #2)

dislike 0 like

(a) 81 mm

(b) 82mm

(c) 95mm

(d) 240 mm = 24 cm

Join to answer this question

Join a community of thousands of dedicated teachers and students.

Join eNotes