optics
Thin Lens Equation
$$\frac{1}{f} = \frac{1}{d_o} + \frac{1}{d_i}$$
Snell's Law
$$n_1 \sin(\theta_1) = n_2 \sin(\theta_2)$$
Fourier + Inverse Fourier Transform
$$X(\omega) = \int_{-\infty}^{\infty}x(t)e^{-j\omega t}\,dt$$
Light Wavelength and Frequency Relationship
$$c = \lambda f$$
Photon Energy
$$E = hf$$