for the rest of the info need to make a remote.
A good point made by jphphotography
is that different cameras may need different voltages.
You may be able to find what voltage your camera needs from http://chdk.wikia.com/wiki/CameraFeatures
Using 3 alkaline button cells (1.5v each) this circuit gives a 4.5V output from the push button and about 3.9V from the IR receiver (the slightly lower voltage from the IR receiver is due to the diode). I think these voltages are likely to be high enough for most cameras, but if the IR receiver voltage output is too low I would suggest using a low voltage drop diode (e.g. a Schottky diode).
Notes on alternative power supplies:
I would not recommend powering this circuit off anything other than small batteries like button and coin cells. The small batteries have high internal resistances which can act as a bit of a safety mechanism if anything goes wrong.
The supply voltage for the IR receiver should not exceed 5v, nor should the signal voltage to the camera.
Notes on the IR receiver:
There are probably a lot of other IR receiver modules that could do this job the SFH 5110-38 was just what I had to hand. You may even be able to salvage a suitable receiver from a broken TV (or anything which had a remote).
Normally when using this type of receiver you would have to use some form of power supply smoothing and use a full 5V power supply. Because this circuit is so simple there is little to interfere with the receiver so it still works very well.
Here is the circuit: