In the essay on the palantiri in Unfinished Tales, we are told that the palantir of Minas Tirith was designed to interact most with the palantiri of Gondor, of which only three remained, one in the hands of Saruman, the other controlled by Sauron. Only a strong will and the right to use them enabled Aragorn to wrest the stone of Orthanc from the will of Sauron. Presumably Denethor started using his stone before the return of Sauron and would have been free to turn his attention wherever he wanted, but his interest was Gondor and its enemies, not distant Elvish realms which were probably screened by the power of Vilya the Elven Ring. He may have conversed with Saruman, a similarly proud individual. However Sauron would change all of this and he exerted control over what the other two keepers of the Palantiri could see, which was largely images of his huge armies gathering to overwhelm all opposition. He may have stopped them conversing with each other. By that time Denethor would realise that trying to look at Imladris would draw the Eye there. He was not happy about sending either of his sons on the quest; only Boromir's stubbornness saw the quest happen at all.

In the essay on the Palantíri in Unfinished Tales, we are told that the palantír of Minas Tirith was designed to interact most with the palantíri of Gondor, of which only three remained: one in the hands of Saruman, the other controlled by Sauron. Only a strong will and the right to use them enabled Aragorn to wrest the stone of Orthanc from the will of Sauron. Presumably Denethor started using his stone before the return of Sauron and would have been free to turn his attention wherever he wanted, but his interest was Gondor and its enemies, not distant Elvish realms which were probably screened by the power of Vilya the Elven Ring. He may have conversed with Saruman, a similarly proud individual.

However, Sauron would change all of this; he exerted control over what the other two keepers of the Palantíri could see, which was largely images of his huge armies gathering to overwhelm all opposition. He may have stopped them conversing with each other. By that time Denethor would realise that trying to look at Imladris would draw the Eye there. He was not happy about sending either of his sons on the quest; only Boromir's stubbornness saw the quest happen at all.