Question regarding Lens Maker's Equation and Thin Lens Equation

[thechairman]

I sometimes have trouble knowing when to use either of these equations in predicting focal length, object length, image length. or is the thin lens equation just a special case of the lens maker's equation?

Is the 1/f term in the lens maker's equation the same as the 1/f term in the thin lens equation (and hence, equal to power)?

also, does anyone know whether compound lens problem likely to show up on the MCAT?



one last thing, i'm having some trouble applying the physics of optics to the structure and function of the eye. Is there a good MCAt book out there that explains this feature?

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[Tan008]

not sure what you mean by compound lens problems, but one of the practice AAMC passages dealt with double lens/mirror systems, but the questions were pretty straightforward.

 

[jochi1543]

I sometimes have trouble knowing when to use either of these equations in predicting focal length, object length, image length. or is the thin lens equation just a special case of the lens maker's equation?

Yes. A "thin lens" is a lens whose radius of curvature is very lage compared to its diameter, but technically, you could still apply Lensmaker's equation. You will need to know the refraction index of the lens and/or radii of curvature to use the Lensmaker equation, so if your problem doesn't mention any of those, it is probably safe to assume that you need to use the thin lens equation. I am currently suffering through optics in my physics class and I have to note that NONE of the problems in the book that concerned the Lensmaker's equation asked for object and image size or distance - they were all about radii of curvature, index of refraction, and focal length.

Is the 1/f term in the lens maker's equation the same as the 1/f term in the thin lens equation (and hence, equal to power)?

Yes.

 

[thechairman]

Yes. A "thin lens" is a lens whose radius of curvature is very lage compared to its diameter, but technically, you could still apply Lensmaker's equation. You will need to know the refraction index of the lens and/or radii of curvature to use the Lensmaker equation, so if your problem doesn't mention any of those, it is probably safe to assume that you need to use the thin lens equation. I am currently suffering through optics in my physics class and I have to note that NONE of the problems in the book that concerned the Lensmaker's equation asked for object and image size or distance - they were all about radii of curvature, index of refraction, and focal length.

thanks, could you answer a quick question for me?

if the thin lens equation is a special case of the lensmaker's equation, why is it that for the lensmakers, there is a negative term (1/r1 - 1/r2), whereas for the thin lens equation the terms are positive (1/p + 1/q)?