I think a little more detail will help. What are the blinds? How many players are left/are you going heads up? It sort of sounds like heads up since you mention only an opponent having 1800.
I actually just mentioned this in another thread, but I've started to count how many big blinds I have through the course of a game. This is useful in heads up or in a table full of players. Previously, all too often, I used to go heads up make a few bad calls and then find myself incredibly short stacked. So keeping tally of my big blinds help.
Here's an example: If you have 1500 chips and the blinds are 200-400 (no antes for the sake of simplicity), I have less than 4 big blinds and very close to being blinded out if you don't make a move. That's not a whole lot of blinds left so I would be thinking all in with almost any pocket pair of 7's and above (perhaps even lower pocket pairs too if I'm desperate), as well as cards like AK, KQ.
But if you have 1500 chips and the blinds are 50-100, then you have 15 big blinds so I wouldn't look to go all in just yet. Think about moving all in? Yes, but not unless I have a really strong hand.
I hope this answers your question...or at least part of it.
EDIT: Oops, didn't realize there was another topic with similar responses. My bad, newbie mistake! And of course, now it dawns on me that HU = heads up. Wow, do I feel stupid or what!!!