There is not only Magic Lantern to get the juice out of your Canon DSLR, CHDK is a firmware extension for Canon PowerShot cameras (with many many supported PowerShots):
CHDK is a firmware enhancement that operates on a number of Canon Cameras. CHDK gets loaded into your camera’s memory upon bootup (either manually or automatically). It provides additional functionality beyond that currently provided by the native camera firmware.
To see all features click here, for an overview go here. So, what do you need if you want to send images from the stratosphere to the ground? A lot of stuff I guess, but for the photographic part you’ll not need the high end gear you may think. Chris Stubbs is an apprentice electronic engineer who started a pretty cool project concerning high altitude balloon flights. To shot images he uses a Canon PowerShot A530 (here on eBay) with CHDK installed, and a cheap Radiometrix NTX2 FSK radio module that is so small it fits into the battery compartment.
There are a lot of technical details in Chris’ post, the project is described in every detail. Not a DIY weekend project but something you could replicate with a bit of patience and some technical skills.
Ready to go high (image credit: Chris Stubbs)