Jpeg and image size....

What is the difference in jpeg fine, normal, basic, and which is better, if you choose to shoot jpeg? Image size....how much does the jump from medium to large on your camera effect the image quality?

 

Always shoot in large. There is no question about it, setting the size to small or medium reduces the number of pixels recorded. Fine normal basic settings are to do with JPEG compression. I for one can not see a difference between fine and normal so if I do shoot in JPEG I shoot Large - Normal. But with basic the blocky compression artefacts become very apparent and you start losing detail.

 

I always shoot in LARGE too... it means you can blow up the pictures larger without them looking pixelated. For my Nikon, a "Large" file can be printed out nicely as big as 12 x 18 inches. Whereas "Medium" is only good up to a little larger than 8 x 12 inches. Maybe 11 x 14. But it's a lot better to shoot in Large I think.
I too, can't see a difference between FINE and NORMAL so I always just use "Normal" -- it uses up less space on your memory card.

 

The differences between "fine, normal, basic, etc" depends on the manfacturer of the camera and how they have setup the quality definition for those images.

Generally speaking:

Basic - low quality - alot of compression
Normal - ok quality - more compression
Fine - good quality - some compression
SuperFine - great quality - little to no compression

The more compression, the more data is thrown away in JPEG. It is a "lossy" data format. The more you throw away, the smaller the filesize... but it also means more artifacts and "blocking" in the final image. If your camera has a good deal of signal noise/grain, then jpeg magnifies that noise, making your photograph look worse. The difference in quality depends, once again, on how the manufacturer has configured the settings.

Unless you are pressed for space on your memory chip, you should typically shoot with the fine or superfine setting, so that you can use the image for web/print purposes.

 

The following are my observations only, featuring my opinion, and I don't claim to be offering any expert advice or information.

Without getting into a lot of details, the way that the different manufacturers set their compression levels is a closely guarded trade secret. They will not tell you exactly when and where things like oversampling or subsampling kicks in on compression. It is not important that you understand how this works, it is only important that you have a set of eyes. You can zoom in to see what (if any) compression artifacts are visible, and choose the level you feel most comfortable with.

Compression generally is different even between the image sizes of your own camera... for example, the software MAY compress Large-Basic and Medium-Basic differently.

I generally shoot Large-Basic on my D80's and Large-Fine on my D40, because the D80's Large-Basic is virtually impossible to tell from Large-Fine on even a 24x20 print, because the Large-Basic really isn't very basic. On the D40, there is a HUGE difference... obviously, the subsampling settings are quite different between the two image processor.

I don't have a clue on Canons, and I don't use photoshop for compressing JPEGs, so I don't know where the quality really starts to degrade... but there is definitely a point that it does.