Hi Doug
the Canon will require around a 1.5Amp (peak) psu, maybe even slightly more (depends on if you use a lens on it and auto focus etc etc), so the 7808 will be running very very hot. A few users here have built varying camera PSU's using various methods, see
here,
here and
here.
further to this voltage regulators device mfgrs recommend around 2.5V head room (in-put) voltage above their regulated voltage to regulate efficiently. In experience I found you need around 2V min above regulated voltages. You can get low drop-out regulators (LDO's) that will operate ok from a lower headroom voltage.
A better method is to use a high efficiency switch mode regulator (see links). They operate with far less heat waste and are very stable. I saw a few gents obtained cheapish regulators from fleabay and they said they work ok. You need to look on CN for info on this, I'll see if I can find the posts on this.
Lastly typical voltage regulators like 7808, 7805 require around a .01micro farad ceramic bypass capacitor on input that helps filter high freq noise oscillations and fix what is called Equilivent series resistance (ESR). Linear regulators don't like capacitive loads. This bypass capacitive value is usually listed in the OEM part data sheets. Sometimes a small electrolytic is used as well lets say 1.0 microfarad.
Hope this helps.
edit:
Here is one of the cheap fleabay DC converter modules. 4 to 35VDC in for 1.2 to 30VDC out (adjustable)...2Amps for $2.14.
Another rated to 4A for $3.39. I like this one.
