Hey, all, thanks for chiming in!
Anyone with an ZS40, would you double-check its behavior, please?
Mine definitely does NOT save the shutter speed or aperture.
I just tested this again to confirm. I put mine into the M mode, set the shutter speed for 4 seconds and the aperture for 3.3. I went to Menu, then Set Up, and tried saving it under Custom Set Mode, C1.
Fine. I can now turn to C1 and it shows up. However, it didn't really save shutter speed and aperture at all.
Test 1. Go to any other mode (e.g., back to M) and change the shutter speed, then go back to C1 and the shutter is the new speed you just set, not the supposedly saved one!
In addition, whatever shutter speed you just set overrides whatever you previously saved to C2-1 or C2-2, etc. Kind of defeats the purpose of the custom modes, eh?
Test 2. Next, turn off the camera. Turn it back on. Each custom mode remains at the last shutter speed and aperture you used, not whatever was originally saved with that particular mode!
Test 3. Try setting a different shutter speed for C1 and C2-1. It cannot be done. Whatever the last speed was is what will show when switching to the other mode.
Test 4. Repeated the above, but used the S mode. Same results. Phil seems to be right: "the camera [is] just recalling the last used manually set value".
Why does this matter? See the original post. But here's a richer explanation.
One would like to have a setting for, say, sports; another for, say, starry nightscapes (long shutter, high ISO, wide aperture, Tungsten white balance, & whole-field metering); and yet another for, say, the Moon (fast shutter speed, narrow aperture, daytime white balance, and spot metering).
I'd like to be able to switch easily among them, without having to putter to set each individual parameter. Note: It's not that you're stuck with that; you can always tweak each setting on the fly. But, whenever you want to get back to the original, a simple twist of the dial, or selection of a single menu item gets you there.
Other cameras. I've tested this on a Canon SX700 and A650 and they definitely save shutter speed and aperture, no matter what else you do in the other modes and they save the Custom setting between power off and on.
The ZS40 is so tantalizing with its 4 custom modes, but it doesn't seem to do this... unless there's some step or setting I've missed here!