I think the most common approach with automotive system power supplies is to use a voltage regulator circuit. Voltage regulators will smooth out the input voltage and drop the value down to the desired voltage. Since automotive systems feed off of the alternator, there is the potential for some pretty nasty voltage spikes (Some have seen up to 60 volt spikes!!!). These voltage spikes will cause problems for circuits which are designed to run from a specific voltage range, such as your camera equipment. Thus, the use of a voltage regulator will smooth these voltage spikes into a very uniform voltage, say 7.5 volts.
There are several different types of voltage regulators. Some will regulate only positive voltage, others will only regulate negative voltage. Some are designed to output a fixed voltage, some will output an adjustable voltage. Some will only handle 500 mA, some will handle up to 5 amps. To see National Semiconductors product line for voltage regulators, check here: You'll be able to see the capabilities of each regulator.
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For your ouput voltage of 7.5 volts, you'll probably have to go with an adjustable regulator that is capable of delivering 2 amps (SEE LM350 part number).
The voltage regulator datasheets (obtainable from the link above) will provide operational circuits for the given regulator, as well as how to calculate the other component value to output a certain voltage.
Be advised that voltage regulators produce heat, for the amount of voltage that they are reducing from the supply. The heat is also proportional to the amount of current that you demand from the regulator. Thus, heat sinking the regulator is almost always necessary, especially if you are drawing 2 amps, and regulating the voltage from 12volts to 7.5 volts. Consult the datasheet for the heat characteristics.
So, I suppose a little studying of the datasheets, and a little design work is in store for your application. I hope that this helps.