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Q & A: Lens diameter and focal length?

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Lenses & Mirrors
Most recent answer: 09/23/2011
Q:
I Want to construct a simple(i.e.not costly)telescope, so,please i want some guidence for that. How to connect the relation between the diameter of lens and its focal lenth? thank you! AVINASH
- Avinash (age 32)
pune,maharastra,INDIA
A:
The diameter of a lens does not affect the focal length, f, which is give by
\frac{1}{f} = (n-1) \left[ \frac{1}{R_1} - \frac{1}{R_2} + \frac{(n-1)d}{n R_1 R_2} \right],
where n is the index of refraction of the glass, R1 and R2 are the radii of curvatures of the front and back surfaces and d is the thickness of the lens.   The diameter does not enter into this equation.   The diameter, D, affects the light gathering power and the resolution.   
LeeH

 

(published on 09/23/2011)

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