All you need is the 3-pin IC and 2 resistors and a non-critical input capacitor. Do some google-searching on LM317 circuits and you'll find all the info you need.
1.5 amps is barely within the capacity of a 317, but with such a low delta-V across it, the typical part will do it. A minimum spec part might current-limit.
An LM338 is a beefed-up version of the 317, capable of 5 amps.
Both of these parts (and all the LM78xx series as well) require 1.5 to 2.5 volts of "headroom". I.e., the input must be higher than the desired output by this amount, or they'll go out of regulation (the output will start to drop).
So the 78xx and 317/338 might be marginal as the battery voltage drops. There are "LDO" 3-pin regulators as well (Low Dropout Voltage). There are dozens of different part #'s, and they need more care with capacitor selection. Most LDO's in this current range will still need around 1 volt of headroom.
I can't remember the adjustable-version part# off the top of my head, but you might do some searching on LM2930, LM2931, and see what you find. Better yet, hit the National Semiconductor website and search by category. I.e. "voltage regulators", subcategory "low dropout", etc. etc...
4 NiMHd rechargable batteries in series total are about 5.6v (about 1.4v each) and they'll keep on running the camera even when the voltage drops down to 4.5 (maybe even 4.2v when the camera is working)
I can take 4 alkaline AA batteries the multimeter indicates like 4.8 volts...yet when I try to run the camera....Zilch!
Of course you know the reason why...it's open voltage...not voltage under load.
I thought of using a 6v SLA battery(if I could have regulated the voltage to 5-6volts) but since the 5v input doesn't work anymore I've found it's much easier to just keep 2 or 3 sets of NiMh AA batteries charged up.
So are you sure you need exactly 4.2 volts? Mine works just fine on 4 NiMh AAs. 6.8v - 4.5v.(open voltage) ( :>) Norm
You may have to mount the transistor on a heat sink. The heat sink would have to be isolated electrically from ground, unless you can get an insulator for the transistor. It's a mica washer. Radio Shack used to carry them for the 2N3055 and other transistors with the same shape as the 2N3055 (a flat oval called the TO-3), but they discontinued it. Some stores that carry a lot of inventory may still have a few of them left. It's called "transistor mounting hardware". If you use a transistor that has the TO-220 shape which is rectangular with a tab and hole for a screw, Radio Shack still carries mounting insulators for them. So that might be the way to go. The TO-220 transistors are easier to deal with anyway, since you don't need to drill holes for the leads to go through the heat sink, like on a TO-3.
With a pass transistor your regulator chip won't even get warm, at the current level we're talking about.
