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# Factors affecting the focal length of a lens watch

1. I've a couple of which I'm certain such as the thickness of the lens, the curvature of the lens (related to thickness), but I'm not sure about why the diameter affects the focal length. I understand that the thicker the lens, the more curvature present which results in a shorter focal length as the 'rays' converge earlier.

I need approximately 6-7 to talk about in depth. I know there's tons of the internet, but I'm finding it difficult to separate the reputable sources from the 'not so reputable'.

Any help would be appreciated, preferable within the next hour or so, if not later.

Also if you had any suggestions for other methods used to calculate the focal length, that would be much appreciated - currently the ones I can remember from the top of my head - something using a lamp and focusing the image - holing the lens above the table until the light is in focus - something to do with a screen?
2. Look up the lensmaker's equation for the factors that determine the focal length.
3. These are the factors I've currently got:

*Thickness
*Curvature – measure radius of curv
* material of lens
*refractive index of the surrounding medium
*colour of light –
* angle of the lens –
*diameter of lens

I haven't explained how each of them work in case someone else is doing the same controlled assessment and steals all my 200+ hours of research...

I'm using the lensmakers equation in my main investigation - but I have to talk about ALL the possible factors I could study.

Are the factors above right? And are the any others I could mention?

For the radius of the curv of the lens - I found an equation to use but I'm not sure whether you receive the same focal length from using the lensmakers equation? :

1/f = (n-1) (1/R1 - 1/R2 + .......

I can't be bothered typing it all out.

Any help would be appreciated!

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Updated: March 10, 2013
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