Roger Cole
Subscriber
You're buying used so make sure you have warranty or money back - buy from a reputable seller.
Depending on where you are, quality lenses for either are at a premium but Nikons are generally less costly then Olympus because there seems to be more available. The F3 can use none AI lenses which are also generally less expensive then the AI or newer lenses. There are an abundance of screens and finders for the F3 so there is bound to be one you prefer. Also, the F3 viewfinder is 100%.
On the OM4, you have the most sophisticated metering of any camera. While it's exposure range is just less then the Pentax LX, it adds spot metering that the was not common. The OM4 - actually all OM's, are smaller and lighter then the F3 and so are the equivalent lenses. The OM's maybe the gem of cameras but they are robust.
Not to add to the decision dilemma, but in this level of cameras, the Pentax LX is a worthwhile consideration if not the leader of it's class. Almost the size and weight of the OM's, sophisticated flash and TTL metering as the OM4, interchangeable finders/screens like the F3 and the hybrid mechanical/electronic shutter giving you much more shutter speeds available when the battery dies like the Canon new F-1.
I have a Pentax LX. It's a great camera, BUT there are a couple of things to be aware of.
The automatic mode has no exposure memory lock. I'd become so used to this in other automatic cameras I took it for granted. Frame to meter the desired areas, lock exposure, re-compose. On the LX that requires using manual mode or adjusting the compensation for the equivalent exposure, which is not that easy, basically impossible with the camera to your eye. I think this is the one thing lacking in this otherwise excellent camera.
Another thing is that it is rather loud. I can't really quantify this, and it isn't thunderous or anything, but my little Ricoh XR-7 second body is much, much quieter (and has the exposure memory lock - in some ways it's actually nicer to use but built like a toy compared to the tank-like pro grade LX.)
Another thing that some people don't like is that the way the mirror lock up and self timer are controlled, there's no way to use both. You can't lock the mirror up and then have the self timer fire the camera. If I used the self timer that might be a limitation, but I don't so it's a non-issue for me.
The LX does have an excellent meter with off the film metering including OTF flash metering with the proper dedicated flash units, superb low light response, interchangeable finders etc. plus all shutter speeds from X (1/75) to 1/2000 are usable without batteries. It's a great camera, but (like any other camera I've ever used) not completely perfect.