My wife got herself a Nikon D700 and a 135mm F/2 VC lens on Monday. It’s a significant upgrade compared to my D200, because of the FX sensor, but I was mostly interested by the 135mm lens that she got. It’s a lens that enables you to control the focus and defocus, as Nikon puts it.
Basically, it lets you control the amount of bokeh in your photos. Anyway, it’s supposed to be a great portrait lens. I found it really nice to take photos of bikes.
I spent most of the day reading up on differentiable manifolds, Riemann surfaces, germs, and sheaves. Some of the concepts are extremely interesting since they tie into category theory. This led me to differential geometry. I supposed that differential geometry had more to do with Euclidean geometry, an undergrad class that I didn’t enjoy all that much³, but it’s got a lot more to do with the geometry and structure of differentiable manifolds, which interest me¹.
Since the late nineteenth century, differential geometry has grown into a field concerned more generally with geometric structures on differentiable manifolds.