I have iMac 2011 with ThunderBolt and MacBook Air 2011 with Mini DisplayPort. Can I connect them with a ThunderBolt cable? It is for work in Photoshop on two displays. Thanks!
To use Target Display mode with a Thunderbolt equipped iMac you need another Thunderbolt equipped Mac and a Thunderbolt cable [emphasis is mine]:
If your MacBook Air has Mini DisplayPort then it will not work. More here about what options will work.