When I did my photography with film I used to sweat when the film speed (ISO) got to 400. If I was lucky and everyone stood real still I might get a good shot off. When I got my Nikon D70 that number got bumped up to maybe 800 in really good conditions.
I took the following images off the web site
http://www.dpreview.com/ they were taken with a Nikon D700 that was introduced back in '08.
The relief was taken at ISO 6400, the fruit at ISO 25600.
How much easier would natural light photography be with this kind of equipment?
Today this camera cost $2,398.99 (body only) at B&H photo on the web. Not a cheap camera. However, there are some recently released cameras that can be had for under $1000, and these cameras will take really good quality photos at very high ISO's, relatively speaking. Like maybe the Canon EOS 550D, or the Nikon D5000.
But ISO 25600? This is like midnight in the garden.