How far from camera person should stand?

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Homework Help Overview

The discussion revolves around a photography problem involving a 35 mm camera with a 50 mm focal length, tasked with determining the appropriate distance a person should stand from the camera to achieve a specific image height of 30 mm for a 175 cm tall object.

Discussion Character

  • Exploratory, Mathematical reasoning, Assumption checking

Approaches and Questions Raised

  • Participants explore the relationship between the height of the object and the distance to the camera, questioning how to connect these variables. There are attempts to apply the lens formula and magnification concepts, with some participants correcting unit usage and discussing the implications of their calculations.

Discussion Status

The discussion is active, with participants providing guidance on the application of relevant equations and correcting each other's misunderstandings regarding units. There is a mix of interpretations regarding the problem setup, and while some participants express confusion, others seem to arrive at a clearer understanding.

Contextual Notes

Participants are working under the constraints of a homework assignment, which may limit the information they can use or the methods they can apply. There is also a mention of the need to consider the viewfinder distance, which adds another layer to the problem context.

agentas
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Homework Statement



A 35 mm camera has a lens with a 50 mm focal length. It is used to
photograph an object 175 cm in height, such that the image is 30 mm high.
(a) How far from the camera should the person stand?
Answer is
The person should stand 297 cm away from the camera.

Homework Equations


1/f=1/o+1/i
m=i/o


The Attempt at a Solution


1/50=1/o+1/i
m=30/175=i/o
I really do not know how to relate height of the person to distance to the camera .please help someone!How to get this answer?297cm?
 
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Hi agentas! :wink:
agentas said:
A 35 mm camera has a lens with a 50 mm focal length. It is used to
photograph an object 175 cm in height, such that the image is 30 mm high.

m=30/175=i/o

nooo :redface: … 3/175 … look at the units!

Try again! :smile:
 
tiny-tim said:
Hi agentas! :wink:


nooo :redface: … 3/175 … look at the units!

Try again! :smile:

you look yourself. Iam using cm instead of meters.What does not change anything.
 
agentas said:
you look yourself. Iam using cm instead of meters.

Yes, 3cm/175cm. :smile:
 
If u is the object distance and v is the image distance, then
m = v/u = i/o.
Now 1/f = 1/u + 1/ v
Multiply by u to both side. you get
u/f = 1 + u/v = 1 + o/i.
Now solve for u.
 
Uh guys? Zero.

The person should stand close enough to the camera to look through the viewfinder!

Of course, that doesn't say anything about how close the object should be...

:wink:
 
rl.bhat said:
If u is the object distance and v is the image distance, then
m = v/u = i/o.
Now 1/f = 1/u + 1/ v
Multiply by u to both side. you get
u/f = 1 + u/v = 1 + o/i.
Now solve for u.

thanks I got the right answer :)
 

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