At the moment we've got the camera, the stock 18-70 kit lens, and an old Minolta 50mm 1.7 prime. So not a lot of gear really. Neither of us are impressed with the quality of the photos coming from the A200, as you've mentioned in low light it doesn't do a very good job. Blacks are very lacking. It's also annoying that when trying to get photos to do HDR the camera will only shoot one stop up and down automatically.
The 18-70mm kit lens is a bit rubbish (mine sits on the shelf as I replaced it with the Sigma 18-50mm f2.

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Sony ditched the 18-70mm kit lens, so all newer Sonys come with an 18-55mm.
The blacks are easily sorted either with a quick edit in Lightroom/Photoshop, or you can adjust the settings a bit on the camera menu under "Creative Style". You'd also find the colours (and blacks/contrast) will be better with better lenses.
As for bracketing you'll have to change camera for better options there.
I bought the camera a few years ago (before the other half and I got together) without doing any research, just a Sony fanboy and the camera was within my price range. She used to use a Canon 500D, so you can imaging the Sony is a bit step down.
Yup, the Canon 500D is better than the A200, not surprised she'd find it a lesser camera.
Seeing as we want a 10-22 wide angle lens, a new general purpose kit lens, then a zoom lens (200 to 300) of some description, it seems am opportune time to consider a new body as well.
If you're buying all new lenses, then you're talking about quite a bit of cash. If you look at Sigma and Tamron who make lenses for both Sony and Canon cameras, then the prices will be pretty much the same.
Sigma 10-20mm f4-5.6 - £370 (
Sony fit Canon fitTamron 17-50mm f2.8 - £280
Sony fit Canon fitTamron 70-300mm - £280
Sony fit Canon fitSo yes, if you're going to invest in all that, you want to make sure you buy it for the right camera.
The above will cost you £930 total, for either Sony or Canon. Then sell your A200, and spend either £300 on a Canon or a Sony.
If you buy a Canon, you can sell your 50mm prime for about £70 and buy a Canon 50mm with that cash.
Are any of the newer Sony's much better? If so, it could be an option to buy a better Sony and then replace the lenses one at a time. Do all of the Sony's have stabilisation built into the body as standard?
Yes all Sony's have stabilisation (Sony call it "Super SteadyShot").
Newer Sony's are better, but all the newest ones are SLTs, ie the mirror is translucent and doesn't flip up, meaning you lose 1 stop of light as it passes through to the sensor.
Slightly older Sony's are still proper SLRs, so you don't have that problem. You can get an Alpha 500 or even the semi-pro A700 for £300.
If you are looking at keeping with Sony but upgrading to a new one, look at the A57, A65 and A77 which are very good, despite the SLT technology.
If you were going to replace one lens at a time, I'd start with the kit lens and get either the Tamron 17-50 f2.8 above or the Sigma 18-50mm f2.8 or the Sigma 18-70mm f2.8-4 (if you need the longer end).
If your friends have Canon cameras, do any of them have decent lenses that you might want to borrow?
Borrowing is ok, but never as good as having your own.