Len's Maker Equation

[Jepstein30]

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Been awhile since I took Physics, so I haven't had to worry about optics until I just finished up my physics review...

I'm confused about the len's maker equation. I thought I would have to consider the sign (+/-) rather than just plug in absolute values.

For instance:

Focal length for a diverging system is always negative, therefore.. I'd plug in a negative value for 1/f when using the lens maker equation...


Also, anyone have any good video supplements for light/optics? Specifically interference/diffraction, since I think I'm better off just memorizing some tips/tricks for mirrors/lens.

Thanks!

 

[MedGrl@2022]

Been awhile since I took Physics, so I haven't had to worry about optics until I just finished up my physics review...

I'm confused about the len's maker equation. I thought I would have to consider the sign (+/-) rather than just plug in absolute values.

For instance:

Focal length for a diverging system is always negative, therefore.. I'd plug in a negative value for 1/f when using the lens maker equation...


Also, anyone have any good video supplements for light/optics? Specifically interference/diffraction, since I think I'm better off just memorizing some tips/tricks for mirrors/lens.

Thanks!

check out physics classroom online... also EK has a pretty decent way to remember about the lens maker equation, etc.

 

[dudewheresmymd]

Been awhile since I took Physics, so I haven't had to worry about optics until I just finished up my physics review...

I'm confused about the len's maker equation. I thought I would have to consider the sign (+/-) rather than just plug in absolute values.

For instance:

Focal length for a diverging system is always negative, therefore.. I'd plug in a negative value for 1/f when using the lens maker equation...


Also, anyone have any good video supplements for light/optics? Specifically interference/diffraction, since I think I'm better off just memorizing some tips/tricks for mirrors/lens.

Thanks!

I'm a bit puzzled as well..trying to relearn optics myself. What's the difference between the lens maker equation and the thin lens equation? TBR says the lens makers equation (p. 246) is 1/f=1/s +1/s' but i thought this was the thin lens equation? Can someone clarify?

 

[milski]

I'm a bit puzzled as well..trying to relearn optics myself. What's the difference between the lens maker equation and the thin lens equation? TBR says the lens makers equation (p. 246) is 1/f=1/s +1/s' but i thought this was the thin lens equation? Can someone clarify?

You are correct, 1/f=1/s+1/s' is the thin lens equation, that's applicable only for lenses which which are of negligible thickness. The lensmaker's equation is:

1/f=(n/n'-1)(1/r1-1/r2) where n and n' are the refraction indexes of the media and the lens material, and r1 and r2 are the radii of the curvature of the both sides of the lens. (the lens is not necessarily symmetrical).

The lensmaker's equation is used in the derivation of the think lens equation but they are two different things, I'm not sure why TBR has them mislabeled.

The LME gives you the radii if you want to make a lens from certain material with certain power. The TLE gives you where the image will be for a thin lens with a given power and an object at a given distance.

Also, all the numbers except the refraction index can be either positive or negative. The sign convention is not brief, so I'll skip it.