Narrative Layers

Some Examples from the Works of HG Wells, CS Lewis and (Mainly) Poul Anderson
(i) An omniscient narrator presents a third person account of a single viewpoint character's inner thoughts and outer actions. Two of many such characters in Poul Anderson's works are Dominic Flandry and Manse Everard. This kind of narrator does not (seem to) address the readers. Instead, it is as if we are given direct access to one character's point of view. However, we are of course reading words that must have been uttered or written by someone. But the author himself does not address us directly as he would in an article or an autobiography. Instead, he creates a transparent, almost invisible, narrator with unlimited access to the viewpoint character's innermost memories and thoughts, a curious fictional construct. We (usually) assume that there is no such observer in reality - nor do we assume the literal existence of such an observer in fiction although we nevertheless accept his words without, usually, reflecting on them. If the author controls point of view as, usually at least, he should, then the narrator needs to be "omniscient" about only one character - or about one character at a time since point of view can change between chapters or between passages within a chapter but not within a single paragraph or sentence. That way lies incoherence. Coherent prose should describe events that could have happened and each observer experiences events only from his single point of view. There is no point of view jumping back and forth between two or more perspectives.

The narrator might also be omniscient about cosmic events unless, by introducing a first person pronoun, he reveals that he is, after all, one of us, e.g., a novel by Anderson begins:

"Once there had been a great proud star, bright as a hundred Sols."
-Poul Anderson, Mirkheim IN Anderson, Rise Of The Terran Empire (Riverdale, NY, 2011), pp. 1-291 AT Prologue, p. 1 -

- but, further down the same page, continues:

"...we cannot now say. We simply know that..." (ibid.)

A first person narrator has appeared.

(ii) The viewpoint character is a first person narrator directly addressing his readers, e.g., Anderson's Steve Matuchek, Carl Farness or Wanda Tamberly in her first appearance. Such a character is able to tell us what s/he feels and thinks and does not need to be mediated by any omniscient narrator.

(iii) HG Wells' outer narrator directly addresses his readers by presenting first person accounts of conversations between the Time Traveler and his dinner guests, then repeats word for word the Time Traveler's first person account of his journey through time. There are two first person narrators but no omniscient narrator. At the end, the outer narrator incorporates his readers into the narrative:

"The Time Traveller vanished three years ago. And, as everybody knows now, he never returned."
-HG Wells, The Time Machine (London, 1973), 16, p. 101.

(iv) We learn that the original of CS Lewis' "Ransom" has told his story to Lewis who gives us a third person account, fictionalizing the names of the human characters. At the very end of the first Ransom novel, what had seemed to be an omniscient narrator turns out to have been a first person narrator:

"At this point, if I were guided by purely literary considerations, my story would end..."
-CS Lewis, Out Of The Silent Planet (London, 1963), XXII, p. 177.

"This is where I come into the story. I had known Dr Ransom slightly for several years and corresponded with him on literary and philological subjects, although we very seldom met." (p.178)

(v) Poul Anderson's Jack Havig had conversed with Robert Anderson who had conversed with Poul Anderson. Using notes left by Robert Anderson, Poul Anderson composed first person accounts of Robert Anderson's conversations with Havig and also third person accounts of Havig's journeys through time, fictionalizing names and some other details as Lewis had done when describing Ransom's journey through space.

Assessment
The outer narrator knew the Time Traveler and Lewis knew "Ransom" whereas Poul Anderson knew only Robert Anderson, not Jack Havig. Anderson introduces one extra layer of mediation. Any more than that would have placed too great a distance between the narrator who directly addresses us and the character whose exploits we should accept while we are reading them.

For more on points of view in Lewis' fiction, see The Ransom Trilogy.