Math in the thin lens equation

  • B
  • Thread starter Kuzon
  • Start date
  • #1
42
5

Main Question or Discussion Point

Why isn't 1/f=1/do+1/di just the mathematical equivalent to f=do+di? Can't you raise all terms in the equation to the power of negative 1 to get the latter equation? The maths of reciprocals is confusing me lol.
 

Answers and Replies

  • #2
That is not the lens eqn.
The lens equation is :- 1/f = 1/v - 1/u
Where v:- image distance with sign convention
u:- object distance with sign convention
just take reciprocal of whole eqn

## \frac {1}{\frac{1}{f}} = \frac {1}{\frac{1}{v} - \frac{1}{u}} ##

## f = \frac{1}{\frac{(u-v)}{uv}} ##

## f= \frac{uv}{u-v} ##

Clearly it is self explanatory.
 
  • #3
539
144
That is not the lens eqn.
The lens equation is :- 1/f = 1/v - 1/u
Kuzon has written a perfectly acceptable version of the lens equation, one that is commonly used.

Kuzon: raising to a power does not follow a distributive law as does multiplication. So we have a(b + c) = ab + ac but (b + c)2 ≠ b2 + c2.
 
  • #4
Kuzon has written a perfectly acceptable version of the lens equation, one that is commonly used.

Kuzon: raising to a power does not follow a distributive law as does multiplication. So we have a(b + c) = ab + ac but (b + c)2 ≠ b2 + c2.
Sorry, I did not know that version of lens equation; as in our country the lens equation version used is different.
 
  • #5
240
42
I have acquired the same as @Sahil Kukreja . The relation is about their reciprocals, and cannot directly be changed to what @Kuzon wrote.
 

Related Threads on Math in the thin lens equation

  • Last Post
Replies
2
Views
3K
  • Last Post
Replies
3
Views
836
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
11
Views
5K
Replies
10
Views
2K
  • Last Post
Replies
3
Views
928
Replies
20
Views
2K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
5
Views
3K
Replies
2
Views
598
Top