Join Date: Aug 2006
For your needs, I think you might be happiest with the SD700 IS. The drawback there is lack of a true manual mode, or even aperture or shutter priority modes. But from what I've read/seen it does such a good job of handling these automatically that you might not miss them. And it does have a long shutter mode that will let you get those night shots you are talking about. Also, while it's high ISO performance isn't in the same league as the F30, it's gernerally good compared to anything else in that range. And the IS will often let you use a lower shutter speed and lower ISO, so the combination in practice will be near as good as the F30 even in most low light shots. And the Cannon will be better in outdoor shots with strong sunlight. It also has the advantage in a number of design/convenience areas, from better battery and storage formats, to a bit better menus, the optical viewfinder, a few more features.
Next is the camera I just ordered for myself, the F30. This has the advantage of great high ISO performance (relative to other compact digitals), as well as a pocketable size, and good aperture priority and shutter priority modes. The lack of a optical viewfinder may be a drawback, but from the reviews I've seen it also seems to have one of the best LCD screens available, and in addition has a button that can be pressed to brighten the screen when needed, which most are saying works well even in bright sunlight. One issue might be that, while the autoffocus generally gets good reviews (aside from being noisy), it apparently struggles at night with long distances. Which would be a problem on those cityscapes and celestial shots you are talking about. On the whole though, this camera seems to be capable of good shots in most any condition, but with some knowledge and work required in some situations. Thus, it seems to appeal more to enthusiasts.
I'll add that while alot of people talk about its low light capabilities, some of the truly "low light" shots (at least those that don't allow for long exposures) will be impressive only in that it was capable of getting a picture at all. Shots at ISO 3200 aren't going to look good, and ISO 1600 isn't that much better (though it's comparable to ISO 400 on most of these others). On the other hand some underestimate how often good ISO performance is useful. One area where this camera truly seems to excel, from some of the user galleries I've seen, is in spacious, well lit interiors, like shopping malls, auto shows, and churches; shots where the outstanding ISO 200-800 performance makes the difference. As for outdoor shots in bright sunlight, it appears that EV compensation can be used to reduce a tendency to overexpose a bit, which also reduces or avoids the purple fringing which is common in some of the high contrast photos in bright light.
As for the Z850, my concern there would be noise. One review pointed out that one reason for poor ISO 400 performance was that it was really operating at closer to a ISO 600 equivalent at that setting. Still, even accounting for that it was still subpar when compared to any recent 6MP or 7MP camera; but that seems to be the tradeoff right now for going to 8MP. It does seem to shine at lower ISO levels, such as outdoors in bright light. Like the F30, it has an outstanding screen, battery life, and good manual controls. Like the Cannon it has an optical viewfinder, very slim compact body, and outstanding menus & features. Like both it is a quick performer. So the only real drawback is the lack of either IS or good ISO performance. Since you aren't printing photos, you might find you get good enough results on indoor shots at ISO 400 to make this a reasonable choice with shots redued to a computer monitor size. But you probably don't really need the 8MP either much, and might be better off with a 6-7MP with less noise.
Looking at a couple of recent reviews, you should really also look at the Sony W100. It's a good pocket sized 8MP point and shoot, with good manual, aperture priority, and shutter priority modes (though no manual white balance), an optical viewfinder, good low light performance, and a high sensitivity mode (and a useful one becuase of relatively low noise at high ISO settings). It uses "MemoryStick" memory, but also comes with a reasonable 64MB internal memory. And it's been getting some good reviews for image quality, including one Steve just posted here yesterday.