Stan,
You stated...
I am trying to find a digital camera with a fairly high zoom that
works well in low light conditions outdoors at the upper reaches of
its high zoom, without flash (specifically, wildlife shots at or
after sundown but before complete darkness, or early morning shots
at or before sunrise).
Your questions with my opinions:
(1.) will the A1 outperform the FZ10 under these conditions?
I have not used the A1 in low light outdoors yet. However, I have used it indoors, low light. It's focusing system was far superior to the FZ10. It focuses slower in dim light but is very fast in normal lighting.
For moving subjects, it is also no comparison, the A1 seems to be designed with action in mind. Besides the fast focus, the continuous focus has a feature that tracks your subject. Have not put it to the test in real life, but it was fun tracking un-suspecting people in the store. I guess that's kind of low light.
The A1 has a bigger sensor that should be better with high ISO noise. It has the option of going to 800 ISO where I think the FZ10 stops at 400.
(2.) if one had to make do with a $1,000 or less I/S zoom lens, would a DSLR - like the Digital Rebel - perform "significantly better" than either of the these two cameras, or just "somewhat better?"
In my opinion, there is no gray area, the D-Rebel with almost any telephoto lens would be better for this challenging situation.
For low light- It seems to me that even an entry level lens with a smaller maximum f/stop would do better on a D-SLR. It's still a bigger lens, collecting more light, and supplying the image to a much bigger sensor. The Sony 828 with its f/2.0-2.8 lens might give a cheep SLR lens a run. Remember, the FZ10 has a smaller sensor than the Sony, so even when they are both at 2.8, the Sony is collecting more light. If the subject is moving, the FZ10's IS is rendered useless.
I can go to ISO800 with very little noise, compared to any of the 2/3" or smaller sensors. This makes even a relatively slow lens useful. Also, if your subject is moving, image stabilization is rendered virtually useless. The FZ10 has a mode that only stabilizes vertically when horizontally panning. The A1 specs say that it automatically detects panning. The high-end canon IS lenses can be placed in a mode like the FZ10's. But when it comes down to it, high ISO and fast shutter speed is the best remedy and I think that is one of the major advantages of the D-Rebel or other DSLR.
The biggest drawback to the D-Rebel is the cost of camera, cost of lenses, and having to carry it all around. Also, it can be more difficult to take a good picture because the depth of field is much small at any given aperture, compared to a smaller sensor camera. However, that small DOF is what makes a good picture of a single subject so compelling.
I guess that what I think you should most note about the SLR lenses compared to the lenses on the FZ10 and A1 is: You don't have to get an f/2.8 lens to reap the same results. This is because the sensors are not the same size and significantly changes things in the DSLR's advantage.
One more point of commentary: I took the A1 and the 10D to a little New Year's Party. After a few shots on both, I put the 10D away and finished with the A1. I learned some things:
1) The A1 is much smaller and easier to handle
2) The A1 is not as intimidating as having this big SLR pointed at you
3) The pictures from the A1 in auto ISO showed noticeable noise in black areas even when only printed at 4x6 size. I think it chose ISO 200 even with flash to increase the flash range in the dark environment. None of that with the 10D until you get into 800 or 1600 ISO.
If you know exactly what you want to take photos of, and it's challenging like your situation, it's hard to go wrong with the D-Rebel. For $1000 you could choose between many good lenses. If you know that you are going to be taking shots of moving objects, I'd say don't worry about IS. It cost about $500 more on the fast lenses. I have the 28-135mm (Equiv. 45-216) IS and I like it allot for everyday. It was about $450. If you want more zoom and want low light action, there are better choices. Sigma makes some good lenses. At
I probably should have put my pluses and minuses together, but here is another, possible, negative for DSLR. Most DSLR's, by design, under process the pictures. The photos that come out are still nice but post-processing is usually necessary to get the most from them. This is less true with the one piece cameras that tend to apply more in camera processing and provide an image that is closer to being ready to print.
Well, I have made this post to wordy. I'd take the A1 over the FZ10 (I returned the FZ10). The D-Rebel would be best in the situation you described, if you don't mind the added cost and larger size and weight. If you want to have a camera that can be used easily and be less intimidating, the A1 might be better. If you can deal with the design and memory sticks, the Sony's have a nice lens and, from the 717-on, are fast focusers.
Mark