New Camera

I would imagine the big change from the 400D-500D would be a higher megapixel count, possibly an improved stock lens (the stock lens on the 450D has been rated as distinctly average), and the faster DIGIC 4 processor.

Having had hands-on with a 50D, it makes the 450D feel like a kid's toy. Fast (6.3fps continuous shooting), built like a brick outhouse, not at all plastic-y. Feels like a "proper" camera.

So I was debating buying one (Jessops have one at a good price with the Canon 18-200 lens), then buying a Powershot G10 for a compact.

I have a Nikon D60. The adjustable auto ISO function is invaluable in low light situations such as tube photography. You can set a min exposure time, at which point it will bump up the ISO if the light is too low. So if for example I know I can hand hold down to 1/15sec (with VR on), then I will set the min exposure to 1/15 of a sec. Most SLRs auto ISO function will ISO bump at a fixed 1/60sec.

14mp is more than enough for the amerture, that sort of size is for studio work and posters only.

More megapixels is in most cases worse, particularly in compact cameras. This is as the megapixel count increases, the size of the pixel decreases. Thus each pixel is getting less light, and the image gets noisier. This isn't much of a problem with SLRs which have relatively large sensors and tend to use cutting edge sensor technology. However with compact cameras with tiny sensors it has resulted in a decline in image quality in the last few years. Even at base ISO, the images from compact cameras suffer from both noise and noise reduction artefact.

Unfortunately as most consumers think that more megapixels is better, the camera manufacturers have to follow suite. BTW, I've had a photo used on the back of an A4 sized book, and it was just 4 megapixels!

Oh, and if you want to find the best prices then this site is an invaluable source:

www.camerapricebuster.co.uk/

You are kind of right, but the number of megapixels cited is always true of the number of sites on the sensor, the individual elements that detect light.

Because a digital photograph is made up from red green and blue light you need three values for each of these sites. The way the vast majority of cameras work though is to have a filter placed over the sensor so that each site only responds to one of those colours. Interpolation is then used to calculate the values for the colours at each site. The most expensive high end medium format backs and cheapest camera phones all work this way.

So a 14 megapixel camera does have a resolution of that many pixels, but two thirds of the colour information is interpolated.

There are only a couple of notable exceptions. Fujifilm use their own Super CCD sensors which have the sites on them laid out diagonally. Traditionally this meant they used interpolation to rearrange the output into rows and columns. It gets complicated with their newest sensors as the megapixels they claim are true of the number of sites on the sensor, but it still needs to do some interpolation to combine the information from them. And it still has the same issue of using a filter and needing to interpolate colour information anyway.

The other exception is the Foveon sensor, which is only used by Sigma and uses a technology where each site on the sensor has a separate red, green, and blue layer to avoid needing to interpolate anything. But being a newer and more expensive technology the sensors do not yet have the same resolution as conventional ones. Sigma's DP-1 claims to be 14mp, as it has that many sites on the sensor, but the resolution is only actually a third of that, making it equivalent to 4.6mp.

So in short, unless you buy a Sigma Foveon (which is unlikely as they are expensive and not as easy to find) or Fujifilm camera, they all work the same way no matter how high the megapixels. They all interpolate colour information, but not detail.

Hope that made sense!