In the past I have used
xfig for such projects. Dispite the interface being very outdated (and the requirement for a three button mouse), the figures it generates are of high quality. You can install it using
sudo apt-get install xfig
Recently I have started to use
Inkscape for figure generation. The program can import/export from/to eps, pdf, svg, and even Latex (through PSTricks).
For drawing circuit diagrams you could import existing SVG graphics of the various components as there are plenty out there on the internet (i.e. see this). Drawing a converging lens diagram like you have above should be fairly easy.
sudo apt-get install inkscape
Please beware that the learning curve for
inkscape is steep. The documentation on how to use the program is good and there are several video tutorials on how to do complex tasks already on YouTube (although frequently for graphical design, rather than technical figures) to help you learn.
I just read a post on superuser that suggests Inkscape isn't the best for such drawings. Instead they suggest Google SketchUp for the technical portion and Inkscape to add extra features to your graphics.