What level of class is this? There are plenty of topics that are interesting.
I think many photographers could benefit from understanding the actual physics behind light polarization. I think there's a fair amount of misunderstanding about what polarizers actually do, and also about what circular polarizers do and why they're needed. But I guess thats technically not the lens.
Chromatic aberration is also pretty interesting. Do many photographers actualy know what it is? You could look into the frequency dependence of the index of refraction of different types of glass, and talk about low dispersion glass.
There's also a lot of interesting developments happening in dielectric coatings these days, which is why they are showing up more and more on photography optics for cheaper and cheaper. They are mainly used for antireflective coatings on filters and on lenses I think. But you could look into how dielectric stacks of thin films can have broadband antireflective behavior.
I think if you're going to do something regarding the bokeh and depth of field I think its probably not the best physics project to look up DOF equations online (which there are plenty) but rather look into the equations that lead to bokeh effects. Such as the deviation of a lens from the 'ideal' shape as you move off of the center of the lens.
There's also a fair amount of interesting topics in terms of defects. How large would a grain of dust have to be on your lens before you can resolve it in the photo?
anyway, sorry, grad student in an optics lab, you tickled my funny bone...