I have a canon powershot sx40hs which I am still getting to grips with. Just been taking puppy pics and must have adjust settings. When I put the pics on computer, some have come up normal size but others small(only fill the middle of screen. )Can anyone advise why this has happened. the more I try to fiddle with settings I will probabaly make things worse.Thanks

You may have altered the number of pixels in the file size,   many digi cameras have the facility to increase or decrease the size of the file.  This is done by altering the number of pixels (2Mg, 6Mg etc. )   this then would show up on the computer as different picture sizes, even though it's a quality change ???  

I have the opposite problem, in that often the picture when transferred to the computer is too big to see more than a snatch onscreen

Go on, get the manual out - you know you want to :-D

Was hoping for a quick fix. manual is stored on pc and massive :-(

Just check your jpeg settings - go to the menu, the shooting or recording (what ever they call it) and make sure the setting is either 2 or 3 stars. Should do the trick - as has been said the number of pixeles = the size so depending on what you want to do with it you can use the most suitable settings.

The other thing you can try is setting the camera back to the factory setting. Can't tell you how because I don't own a Cannon but it will be on the menu some where.

Another idea lots of cameras have their hand book on line so you may find a PDF that will solve the problem.

Here you go

Change image quality page 113, just type the number in the box and <enter> takes you to the page :-D