thickness of lens and its focal length


by wlkks
Tags: focal, length, lens, thickness
wlkks
wlkks is offline
#1
Mar10-10, 02:12 AM
P: 1
I'd like to ask
does thinner convex lens give a shorter focal length?

If so, why is it?

thanks very much~~
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HEM87
HEM87 is offline
#2
Mar11-10, 10:20 AM
P: 6
Hi there,

The focal length of lens depends on curvature of the lens and the difference between the curved surfaces, as given by the lensmaker equation.

[tex]\frac{1}{f} = (n-1)[\frac{1}{R_{1}} + \frac{1}{R_{2}} + \frac{(n-1)d}{nR_{1}R_{2}}] [/tex]

where

f is the focal length of the lens,
n is the refractive index of the lens material,
R1 is the radius of curvature of the lens surface closest to the light source,
R2 is the radius of curvature of the lens surface farthest from the light source, and
d is the thickness of the lens between the curved surfaces

If you reduce d then the focal length increases. If you mean making the lens less curved and hence thinner, then the curvature of the interfaces (R1 and R2) will increase and hence the focal length will increase.


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