Portfolio Image resolutions on iPad/iPhone – medium, large, full versions?

Hey there, I just checked out the site i made (not finished) on an iPad/iPhone and I was horrified to discover that the pictures look awful.

They look fine on my mac. Presume it’s to do with the resolution. Can you tell me what resolution and size I should be uploading the pictures at. Do you have an iPad/iPhone you could look at it on? http://www.stefbastian.com

Thanks, Endrio