The 12" LX200 has a long focal length of 3050. A 50MM eyepiece will give you 61x. That will be a smaller actual field that the 20x binos. I don't remember how to calculate actual field size. I'm not really concerened with that. I know about how much sky I'm looking at, 60x or 100x or 350x it dosent matter what scope or eyepiece. For a give magnification you see about the same amount of sky. There is some difference from scope to scope but it's not all dramatic. For example, with my 40MM eyepiece at 76x I just about fit M81 & M82 in the same field of view. Look through any scope at about 76x and you'll still just about fit M81 & M82 in the same field. Now apparent field is a different story. Appearent filed size is how big the circle you looking at in the eyepiece is. For example, the difference between my 40MM Serius Plossl with 40 degree field and my Meade SWA 40MM 67 degree field is very dramatic. It's the same image just bigger. Like the difference between watching 19" TV and a 35" screen. It's the same picture only bigger. You don't get more stars and the 2 galaxies don't fit any better. But it is a bigger image. Once you get used to a 67 degree field, the 40 degree eyepieces look like your looking down a tunnel to a circle at the bottom. The 50MM eyepieces usually have a smaller apparent field, 40 to 45 degree. Now M81 & M82 will fit better at 61x but they will look smaller in the 50MM than a wide angle eyepiece. I used the Meade 56MM in my scope once, didn't like it. But I guess I'm spoiled. One more thing, you can get a focal reducer that screws on the back of the scope. That will cut the focal length to about f/6.5. that will decrease you magnification and you will see more sky. i.e. M81 & M82 would fit much better in my 40MM SWA with the focal reducer.
That's it;
BOB SAL