Is there anyone here with legal knowledge of criminal law? It...

Is there anyone here with legal knowledge of criminal law?

It was my understanding that once a conviction was made by a jury that the evidence that was presented in court cannot be challenged in an appeal as it has been established as fact.

That an appeal can only be made on new evidence or if an error was made by the judge in allowing certain evidence, or in how they went about instructing the jury etc.

Is this correct?