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HenryHH
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Homework Statement
In a 35 mm single lens reflex camera (SLR) the distance from the lens to the film is varied in order to focus on objects at varying distances. Over what range must a lens of 45 mm focal length vary if the camera is to be able to focus on objects ranging in distance from infinity down to 1.4 m from the camera?
Homework Equations
1/f = 1/p +1/q
The Attempt at a Solution
First, the thin-lens formula is applied for the case of focusing on objects at a distance of infinity:
1/45 = 1/∞ + 1/q
q = 45 mm
Then, the same formula is applied for the case of focusing on objects at a distance of 1.4 mm:
1/45 = 1/1400 + 1/q
q = 46.49 mm
Therefore, the range of movement is 46.49 - 45 = 1.49 mm.
I actually had help from a tutor with solving this problem. I understand the problem itself, but what I don't understand is how q = 45 was derived from the equation 1/45 = 1/∞ + 1/q since the equation contains ∞ as a variable.
Generally speaking, how do you solve equations with infinity (∞) as one of the variables? I am really stumped...