Magnification has to do with lot's of things.
Follows is a post made by BOBSAL a while back.
He explains it very well.
Hope you don't mind the quote Bob.
The highest magnification you can use varies from night to night. The way to tell is to put in a smaller and smaller eyepieces till your not happy with the way it's focusing any more. Then you've reached the max for that night. Of course your scope should be collimated correctly and the sky should be clear. But under any conditions with almost any scope 500x is about all the atmosphere will allow. I saw a 7" APO refractor on the moon at 550x one night and it was swimmy. Looked like it was underwater. Under a stiller sky we might have gotten a better focus, but that's an APO refractor. One of the best focusing scopes theere is. I saw a 4" Takahashi APO refractor at 250X way over the 50x limit of 200x and looked better that anything I've seen. Probably could have gone higher to. But i'm sure we couldn't get up to over 500x. It's a matter of what you call a good focus. I looked at Saturn in my 12" LX200 with a 8MM eyepiece and 2x barlow 762X. It looked like a fuzzy circle with a fuzzy ring around it. That night with a 14MM at 218X I could see the Crepe Ring, the dark ring on the inside of the B ring next to the Crepe ring and the Enche ring in the A ring. It was a spectacular view. At moments of clarity, it started looking like a record album. At 782X it was awful and that was a real good night. With the 8MM alone it was OK, the Cassini division was there and the Crepe ring, but the image degraded enough to loose the Enche ring which was a thrill to see. I'm telling you, it's not about magnification, it's about clarity and sharpness. A smaller clear image is preferable to a large dull one. There's no way to force more magnification out of a scope and get a clear image. Use it at reasonable power 50x to 250x is just fine for almost anything you want to see. I've seen way to many posts where people are frustrated because they think there's something wrong, can't get a good focus at the 50x aperture limit. Like I said, your max magnification is what looks good to you from night to night. I do 70% of my viewing at 138X with a 22MM eyepiece. I go to my 40MM at 76X more often than my 14MM at 218x, why? It foucuses so sharp it almost hurts my eye. Let me give you a quote. This guy looked in my scope with Saturn at 762X, he said,"That looks great!" I said,"What are you talking about, there's no detail, it looks awful". He said,"Yeah, but look how big it is!"