What you are talking about is the size of the sensor itself. A big sensor has more light gathering ability and the individual pixels are larger and tend to have more light gathering ability and will have less noise. That is one reason DSLRs do so well compared to pocket cameras. Their sensors are huge. Some of the high end cameras have 1.7" inch sensors.
Pocket cameras generally have a sensor that are less than 1/2 an inch diagonal, while DSLRs are 1 inch and up.
Up to almost 2" in some cases 
Oh good God. I knew it was complex. Like learning a new language.
I want to make sure you all understand how much I appreciate your time and info. I’m most assuredly not as intelligent as some of you and it will take me a little while to soak this in. Hell, it will take me a whole day just to talk myself into sitting down and tackling it. I would like to maybe post a couple pictures of what I think isn’t good enough vs. acceptable vs. ideal. I hope you’ll all stick with me.
If it is ahy help there are any amount of online reviews of cameras.
This is the camera I used. Chosen not as a result of checking reviews but purely because I have used the Olympus OM series previously.
The Register is not a photographic rag by any manner of means but do conduct some quite down to earth reviews of digital equipment.
It doesn’t have to be a Nikon.
I would love the D90 but it’s out of my budget. I have no aspirations of doing this professionally, but I am the kind that likes to carry a camera around with me on a daily basis. Right now I’m using an 8 year old Olympus C4000, surely I need to upgrade??
This leads me to believe that a nice point & shoot is the ticket for you.
Unless you want to haul a much larger DSLR - and something tells me you don’t (which is perfectly OK) - something you can slip in your pocket would suit you best.
And keep in mind, with a DSLR, the purchase of the camera body is only the beginning. There are lens(es), flash, filters, tripod, software, and various other accessories that can certainly break the bank.
You can ignore these numbers. Once you go much above 400 (800 may be pushing it), your image will be so grainy it will be useless.
That’s not a true statement. If you looked at what was linked above for the D90 it does quiet well.
Sure, it does well for a one-inch image on a computer screen. Show me an 8 x 10 (or larger) print, then we’ll discuss it. The higher the ISO, the more noise. I rarely shoot above 200, and never above 400.
I’ve made 8x10’s from my D-70 at ISO 800 that were better than flash shots because of the guaranteed overexposure of people wearing white. I’ll take noise over images that are overexposed any day. Photo’s taken indoors without the benefit of multi-slaved flash equipment are death with factory flash units. If I bracket it to get rid of over exposure then I have to flash fill it on a computer which… adds noise.
You’re right that more noise will be added as the ISO goes up but there is a trade-off to be made and most people will be satisfied with a 4x6 print if it is well exposed.
The sensors on Nikon DX cameras measures 23.7 mm (0.93") by 15.7 mm (0.62") not the 1.7" you reference. Full frame sensors measure 36 mm by 24 mm which was the size of standard 35 mm film. The multiplication factor for DX lenses is 1.5 compared to a full size (FX) lens. The measurement you are stating is for the LCD display which has nothing to do with picture taking!
All comments after this regarding sensor size are in error.
Well, that one-inch image is a crop–actually three crops, of midtone, shadow, and detail regions. A tiny image of the whole chart setup is shown here (I can’t find a bigger one); if that image is one inch wide then the whole test chart looks like it’s at least a foot wide.
Of course it’s always better to shoot at low ISO if you can. But sometimes you actually do have to push your equipment, and it’s nice to know how far you can push it. This is especially good to know for an everywhere camera, where you probably aren’t going to be carefully composing everything on a tripod; candid shots can’t always wait. And digital cameras have gotten a lot better at high ISO in the past few years, IME.
Another possibility is to buy used. There are plenty of people out there who upgrade to the latest model in a line, year after year. Depending on what features you need, you might be able to buy a two-year-old model a class higher, for about the same price. … I don’t know where you ought to go to buy reliable used equipment, though, unless you happen to know one of these people.
Personally I tend to agree with Mean Mr Mustard that for an everyday camera, smaller is probably better, unless you’re sure you’re OK with carrying a DSLR around all the time. Even if the shot is grainy it’s a lot better than the one you didn’t take because you left the camera at home. (Also I don’t like the user interface on the entry-level DSLRs, but that might just be me.)
(emphasis added)
I appreciate your point about some people just not thinking the quality is worth the extra hassle or expense of a DSLR, but I disagree strongly with the sentiment of the bolded portion of your quote. The quality differences go way beyond resolution.
To illustrate this point, I decided to do a test. There’s a beer bottle on the table in front of me, and I took pictures of it with my point-and-shoot (a Canon PowerShot A770) and with my DSLR (a Canon EOS 450D) and then downsampled the pictures to a web resolution for comparison. I made no adjustments to the lighting and kept the exposure times low to make it more like a real-world I’m-just-taking-a-picture-of-what’s-happening sort of test.
Here’s what the point-and-shoot automatically took. The resolution is adequate, it’s not blurry, you can see plenty of detail. It’s a picture of a beer bottle, and it’s not winning any prizes. It’s also pretty obvious I shot it with a point-and-shoot. I didn’t like the flash overexposure, so I thought I’d also see how well I could do without the flash, and I ended up with this abomination – obviously I had to crank the ISO way up and the results aren’t pretty. Onto the DSLR: first shot. (note: also not winning any prizes, but this picture is about 1000 times prettier than the other two).
You have to admit that the difference is night and day regardless of whether these are only to be used on the web or in small prints.
Nice demonstration, ntucker.
Like everything else in life, DSLR vs. P&S is a series of trade-offs. Each has to decide what they’re willing to sacrifice (inconvenience, learning curve, expense of the DSLR) vs. what they are willing to settle for (the limitations of the P&S).
Now I want a beer. 
You shot a closeup subject, with the DSLR at ISO 800 with a 1.4 lens and compared it to an older compact at 2.8 at 1600 ISO. In pretty low light to boot, she said indoors, and right now Im getting 2.8 at 1/20th sitting in a pretty dark room, so your 1/8th at 1.4 means its awfully dark.
I doubt very much the person wants it for that kind of low light shooting without flash, any more than they want it for long exposure work, its just not what normal people are looking for in a camera.
Frankly even if they do my suggestion would be to get Adobe Elements and try out the noise reduction options in it before spending the kind of money real low light shooting will cost, particularly at range.
My point is that many of the issues are often reduced in impact by smaller images being used, whether its barrel distortion, chromatic aberration, noise or blurring. I agree that low light is one area where compacts will lose, but strongly question whether the person is looking for the level of non flash low light shooting that you’re talking about - even with your 1.4 lens you’re still at 1/8 of a second, and that will be generally useless for most people snapping which I suspect is what the person wants it for.
I think my point stands and the persons stated preference for portability supports my suggestion to check out superzooms pretty thoroughly before considering DSLR.
FWIW, I currently use a 7D for underwater photography, and even there, what can be pulled out from a compact is breathtaking at times, where noise and low light is a constant issue.
Otara
http://www.imaging-resource.com/PRODS/SX20IS/SX20ISLL16007.HTM
http://www.imaging-resource.com/PRODS/SX20IS/SX20ISLL16003.HTM
This is 3 second ISO 1600 and 1/6 second 1600 ISO examples from the SX20IS, one of the cameras offered and in my view looks pretty good at web size. Newer compact cameras have improved/increased in-camera noise reduction, particularly with superzooms.
Also to quote from that site: NOTE: This low light test is conducted with a stationary subject, and the camera mounted on a sturdy tripod. Most digital cameras will fail miserably when faced with a moving subject in dim lighting. (For example, a child’s ballet recital or a holiday pageant in a gymnasium.) For such applications, you may have better luck with a digital SLR camera, but even there, you’ll likely need to set the focus manually.
Ie even with a DSLR low light photography is not a casual activity if this kind of photography is its intended use.
Otara
When someone lists a single dimension for a sensor they are talking about the diagonal measurement. The sensor you list is 1.18 inches diagonal. A high-end camera like the Nikon D3 or Canon EOS-1Ds Mark III has a diagonal measurement of 1.7 inches.
http://www.imaging-resource.com/PRODS/D3/D3DAT.HTM
http://www.imaging-resource.com/PRODS/E1DSMK3/E1DSMK3DAT.HTM
It is pretty obvious why this size is popular for many professional DSLRs, since that is the size of 35mm x 24mm film. I remember back in the old days when professional photographers would buy digital backs for their cameras, so they could switch from digital to film and use the same camera body and lens.
Even with a digital SLR body, you can still use your old SLR lenses, as long as the sensor is not larger than the film the lens was designed for. So, with my Canon DSLR with a crop sensor 22.3 x 14.9 mm, I can (and do) use lenses designed for 36 x 24 mm film or sensors. So, for example, I have a 50mm lens, which performs like a 80mm lens would do on a 35mm film camera.
This isn’t really true - it’s one reason I went from Canon to Nikon.
I had Canon FD and FL lenses for my F1 and A1, and none of them fit Canon DSLRs.
It’s almost true for Nikon - Current Nikon DSLRs will mount 50+ year old Nikon lens, albeit in 100% manual mode.
I said “old lenses”, but (of course) it depends on how old “old” is 
