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Question: Expandable ISO's What does "expandable to" ISO's mean? AKA: ISO 100-6400, "expandable to 12,800.Is this a memory card thing?Hoping for a response, thanksPaul in MN
Document: Honestly, ISO 6400 with extreme noise reduction is usable for publishing to Web after some extreme noise reduction in Photoshop. ISO 12,800 is pointless unless it's the only way you can capture the Flying Saucer. Everyone seems to agree that the ISO levels for the 50D is all marketing and has little to do with usability. However, ISO 3200 is a little better than 30D, but not as smooth as the 40D.- Hot pixels in high ISO - pretty bad, actually in low light.
I bought this camera as an upgrade to my rebel xti, although the rebel xti was an exceptional camera. The Canon 50D blows it out of the water. it has superior build and functionality, great ISO range from 100-3200 expandable to 6400 and 12800 witch is a little to far for my standards. Fast and responsive auto focus, great live view function. I don't really have anything bad to say about this beautiful peace of equipment.
We then took the pictures, compiled them on a single memory card and displayed them on my 46" 1080P HDTV. Results were very much in favor of the 50D. Shot for shot the 50D either matched or exceeded the picture quality of the 40D in all but one situation: indoors with low light and dull colors.
I am surprised to see that the images on the 40D are better than the 50D. I would think logically it would be better to have the CMOS updated on the 50D, but when you compare images side by side 100% crop, the 40D wins. More Pixels doesn't mean better, and that's what the camera factories would want you to believe.
(almost)Though I do feel Canon do need to add more AF points the nine it has seems to do the job well, even when following moving objects it keeps right up with it without a hint of wanting to slow down. Just make sure your memory card can keep up with this camera when your shutter is on auto fire. Like some reviews have stated, I have noticed the tracking does tend to want to go to brighter areas in the frame.
I bought this camera almost a year ago, since I bought this camera it's been in repair 2 times.First time zoom for LCD Monitor stopped working. I sent it to Canon repair center. I have to say that camera was fixed very quickly.But i never got a reasonable explanation why zoom button wasn't working.A few months later my camera couldn't read memory card and also couldn't format it.So i sent it back to Canon repair center.I like this camera.
Images are razor sharp and extremely detailed. I did quite well with 6 mpixels on EOS 10D but this is amazing.Flash card read/write speed: I am using Sandisk Extreme III flash memory cards. It may be even better with Extreme-IV series. Transfer speed from the camera body to the PC and also using a Sandisk extreme  USB 2.0 reader, extremely high. Files simply zap, even 20 MB RAW files...  Amazing!Well done Canon!
However, even the most venerable and expensive lenses are not immune to this problem. I have sometimes seen it on my professional grade lenses such as the Canon 100-400mm f/4.5-5.6 L IS lens and even the Nikon 70-200mm f/2.8 G lens.If you have Photoshop CS3 you can quickly correct this problem. However, that is still one more thing that you have to worry about which increases your workflow.
This seemed to have really increased the light gathering capabilities of the pixels.The Canon 50D ISO can be expanded to 6400 (H1) and 12800 (H2). The Nikon D300 can only be expanded up to 6400. However, on the Nikon D300 you can go from 3200 to H0.3 and then to H0.7 before you get to H1.0 which is 6400.
For example, when in aperture priority mode if the camera detects that the shutter speed selected would result in camera shake it automatically increases the ISO. This feature is available on the Canon 40D. However, the maximum ISO it would automatically set is 800.
Answer: Nothing to do with the memory card.  What it refers to is the sensitivity of the sensor given in ISO speed.  A lower number is less sensitive to light than a higher one and are given in stops like shutter speed and aperature, meaning ISO 200 is twice as sensitive as ISO 100 but two stops less sensitive than ISO 800 and so on.  Usually a higher ISO on digital gives more noise than a lower speed so normally you want to use the lowest setting as practical.  When you read "expandable ISO" I believe that means that the manufacturer is using software to "fool" the camera into a higher ISO rating, you could get ISO6400 by underexposing ISO3200 one stop and raising the exposure in Photoshop to get the same sort of result.  Hope that helps.