Optics: f=R/2 for Mirrors AND Lens?

[rocketbooster]

I always thought you could only find the focal length of mirrors using f=R/2. I'm almost positive that's what EK and BR teach.

I just did a GS CBT and they used that equation to find the focal length of a converging lens. So, um, what's going on? f=R/2 applies for mirrors and lens?

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[BerkReviewTeach]

I always thought you could only find the focal length of mirrors using f=R/2. I'm almost positive that's what EK and BR teach.

I just did a GS CBT and they used that equation to find the focal length of a converging lens. So, um, what's going on? f=R/2 applies for mirrors and lens?

I'm not 100% sure what's in the book (and I'm way too lazy to look it up), but for a symmetric lens of big enough R, f = R/2. That works for solving most MCAT questions. Anything requiring more might prove well beyond the level of the MCAT.

 

[Aggro]

Yea, in every case I've seen so far, the MCAT uses f = R/2 for lenses and mirrors. Yay for simplifying optics.