WARNING: This addon is OBSOLETE and no longer needed! Please remove it from your Interface > AddOns folder. The following two console commands, entered once only, achieves what we want:
/script SetCVar("cameraDistanceMax", 25)
/script SetCVar("cameraDistanceMaxFactor", 2)
IMPORTANT: Make sure to remove ImprovedCamera first!
HOWTO bypass the 50 limit:
WoW has a hardcoded zoom limit of 50, so trying to increase it further by adjusting the above values is utter pointless - don't waste your time on it.
However, there is a way to hack a temporary zoom beyond 50 - perhaps for the purposes of taking screenshots - with an important limitation. You can't change the zoom in-game, and you'll lose the extra distance if you try to change the zoom with the mouse wheel - it'll immediately snap back down to 50 as soon as you do, and you'll have to hack it all over again*.
In preparation, you'll need a text editor capable of editing unix linefeeds - I recommend Notepad++.
1) In WoW, do: /console synchronizeSettings 0
2) Exit WoW.
3) In your text editor, open: <WoW>\WTF\Account\<account>\<realm>\<character>\config-cache.wtf
4) Change the cameraSavedDistance setting to e.g. "250" and save the file.
*You can change the config-cache.wtf to Read-only, preventing WoW from losing your hack if you accidently change the zoom in-game. You can simple, /console reloadui or logout and back in again to go back.