I have an Olympus tough and as much as I love that rugged waterproof camera and as good as the image quality is, I have been wanting a dslr. Because of how expensive they are I think my only option is to buy a used one. I found a Canon Rebel T3 12.2 MP($399), a Nikon D3100 ($225 w/ no lense), and a Sony A230($250). Do any of these stand out as a better deal. I have researched and found very good reviews on the D3100.
But what is the support like for it(lenses, batteries,)?
Also what should I look for when checking out a used camera. Is there anything to beware of?
I don't know a lot about dslr cameras but I am learning so any help will be appreciated.
Generally one of the advantages of dslrs is compatibility of lenses (within a brand/mounting system). First, I'm a Nikon guy, so I can speak to that with a bit more authority, but I'm not going to advocate on Nikon vs. Canon. That's a huge can of worms I don't want to open, but I believe Canon has been similarly consistent as Nikon, so most of what I say will apply within either family. Sorry, I don't know much about the Sony stuff.
Anyhow, with very few exceptions, just about ANY Nikon-compatible slr/dslr lens will "work" on any Nikon body. There are some finer points like "will the auto-focus/auto-metering/vibration-reduction/auto-etc. work on a particular combo, but unless you're mixing very old or oddball lenses with low-end or old-ish bodies, even that isn't much of a concern anymore. Full details here:
http://www.kenrockwell.com/nikon/compatibility-lens.htm
One of the break-over items for Nikon between their "pro" vs. "pro-sumer" vs. "hobby/consumer" bodies is the stuff like "Is there an autofocus motor in the camera body?" If the answer is No, then you only have autofocus when the lens has its own motor (most new ones do). One of the reasons we bought a D90 back in the day instead of the D3100 was because we had a LARGE collection of 15-20 year old Nikon lenses that were right in that zone where the lenses didn't have their own motor. The D90 had a body-motor, the D3100 did not, as I recall. Decision made.
This points to the other thing that happens once you start down the SLR/DSLR path: Lens "Lock-in". You tend to get a collection of lenses, so it's cheaper to stay within a family so you can keep using those lenses. As I said, we have some old specialty lenses (like a 500mm macro lens and some VERY fast prime (non-zoom) lenses that have been in the family since the 35mm days, so it makes sense to stick with what you've got.
The other thing you'll have to decide if you care about (I don't) or just be aware of, is the notion of "Full Frame" (FX) vs. "Crop Frame" (DX) sensors. The best pro-level DSLRs use a sensor that is the same size as a full frame of 35mm film. Less expensive cameras use a smaller sensor, and adjust the optics inside so that it shoots the same image with a "crop". The result for the user is hard to tell unless you're looking at full-frame RAW data for equal-megapixel sensors (i.e. a full-frame 12MP vs. a crop-frame 12MP), but there is one important side effect: The "crop factor". As I said, the cameras with smaller sensors compensate by adjusting the internal optics - this works in concert with the attached lens. If you have a Film/FX lens and Body, everything is jake. If you have a DX lens and body, fine. If you have a lens made for an FX/Film on a DX body, there is a resulting scaling factor equal to the difference in size of the sensor vs. full frame. More info on crop factor:
http://www.kenrockwell.com/nikon/dx.htm
My D90, for example, is a DX with a 1.5x crop factor. The net effect is this: When I use this body with my old 500mm film lens, the equivalent focal length is 1.5x the lens rating, or 750mm! I have a Tamron 18-270mm zoom that is effectively a 27mm-405mm, etc. This can be a plus, (free extra "zoom" on your telephoto lenses!), but comes with a bit of extra baggage, and can be a pain if you're looking for a really short focal length for specific purposes. You'll have to decide if this matters to you. It doesn't affect my shooting much, and I've added an extra lens or two to the collection for the rare time that it matters (like a DX-specific F1.8 "portrait" lens), but otherwise I just keep it in my head and go. The one thing I WOULDN'T do is make a huge investment in DX lenses, because you run into other focal-length issues going the other way if you decide to upgrade to an FX body later.
Regarding "accessory" support - everything but batteries (and a few interface cables) are fully interchangeable across many-decades worth of Nikon stuff. I wouldn't sweat availability of batteries as anything Nikon doesn't still sell will definitely be supported by the aftermarket - there's just SO many of these things still in use.
Lastly, since you're on a budget, I'd advocate you make yourself aware of the concept of the "kit lens". These are the (generally) inexpensive lenses that come bundled with camera bodies. Generally there's one prime and one mid-grade zoom. These work fine, and will get the job done, but they aren't fantastic. There's two ways to look at this. You can see these as mediocre lenses to avoid when shopping - focus on getting the body that meets your needs then buy quality lenses specifically for what you're going to shoot. - OR - look at these as a bargain opportunity. Lots of people who get the "kits" end up upgrading to better specialty lenses later on. They buy a faster prime lens, or a zoom with a bigger range, etc. They may be willing to part with their original kit lenses for a bargain price. Take 'em or leave 'em, but you need to know they're out there until you get a better handle on what you "need" in a lens.
