One of the side effects of the megapixel race is very large pictures. Both in terms of file size and image dimensions. It's long past the point of practical use - as I've implied in earlier articles.
A 4x6 print @ 300 dots per inch (normal printing quality) requires an image 1200x1800 pixels. Although "requires" is a bit strong of a word - most printers will upscale an image anywhere close to that without much quality loss. In effect it's more of an upper limit - in that providing an image larger than that result in 'loss' of detail - there's more information than the printer can actually resolve. That's sometimes a good thing, if your 'detail' consists of messy jpg artifacts and ISO noise - stuff you can see at 100% zoom of Point and Shoot camera shots.
A 5x7 print @ 300dpi is 1500x2100
8x10 is 2400x3000
And so on. To a point.
The larger you make a print, the less likely you'll be viewing it from close up. Meaning you can get away with less detail.
Digital displays are even more forgiving.
Facebook pictures are 720 pixels x (up to) 720 (if you make it square, which most people don't) EDIT - Now closer to 1000x1000, but not all that much larger.
An average photoframe is 800x480
Most monitors display a resolution around 1680x1050 - though some as high as 2560x1600 are getting more common. The first of the two monitor sizes is very close to the size of a sharp 4x6 print.
Televisions, although large, really only display 1920x1080 pixels worth of information.
Which brings us, finally, to cameras.
An A3000, which is rated at 10MP (rather on the low end as of the writing of this article) has a number of settings.
Or 10, 6, 4, 2 and 0.3 Megapixels respectively -- a Megapixel is the height and width (in pixels) of an image divided by a million (and usually rounded a bit). It doesn't really address Aspect Ratios but it's handy for a rough comparison.
A T2i has a number of settings as well:
Or, according to the camera - 18, 8 and 4.5 megapixels
I'll indulge in a little math at this point - also with pictures if you want to skip the number crunching.
Assuming a 300dpi print, you can divide the above by 300 to get the 'optimal' print size.
(I'll omit the lowest setting, 640x480 is only slightly smaller than the current FB size, and is a decent size for emailing pictures)
To visualize the above
So, what does this mean? As covered in the last article, storage space isn't really at a premium most of the time. If you have a fairly good idea of what you're going to do with your pictures (and how much will likely be cropped out, or re-sized) you can probably back your camera off *Max* settings though. If nothing else, you'll be able to copy and email your pictures more quickly.
Myself, if it's something in the backyard that isn't moving and I already have quite a few pictures of it, I'll drop down to Medium (8MP) - and probably Normal Quality (previous article) as well. I can still print an 8x10 as long as I use most of the picture. For Facebook, 4x6 prints and general computer viewing - it's more than overkill.