this guy is tough i know, but any tips please on how to defeat him, my magic seems to have no effect on him

Shoot the Staff of Magnus at the Eye until it reassembles then stab until dead.

Rinse and repeat.

Grab a Sword or Dagger (or something similar, Axes are viable as well. Or so I'm told), and hit him with the pointy end a bunch of times until he lays down for a nap and quits moving.

Use the staff on the Eye until it closes then he will start taking damage from your attacks.

you need to use the staff of magnus to close the sphere , then after a few seconds , Ancano will lose his immunity to damage , and you'll be able to kill him . it helps to be a conjuror , so that you can fight at range and his spells hit your summon instead of you , otherwise use a companion and some gear to resist magic

I bonked him over the head with a warhammer. "You can't defeat..." *SKULL FRACTURE*

I beheaded him, worked like a charm.

Summon an Atronarch, then use the Staff of Magnus on the Eye. The Atronarch will do damage even if you're not close to Ancano, and you can use the Atronarch to herd Ancano for you.

Bashed his brains in with Morag Bal's mace, captured his soul, and feasted on his corpse using Namira's ring.

That other guy killed him before i could blink. The one from the college.

You defeat him as any wielder of magic should, with grace, finesse, a little footwork, and a spell as your song while you perform the dance of battle.

i didnt do this quest till i was high level (49) and he went down with two swiped from war axe

I had to play through that fight a few times. I don't know if I was doing somethign wrong or if it was glitching.

I finally defeated him, walked outside and then promptly got killed by one of those anomalies. Since the game dicided not to autosave for some reason and I forgot to do a manual one. I had to fight him all over again and had them issue.

Most of the time he would take some damage then just stop. No matter what I threw at him his health bar wouldn't move. Eventually he'd manage o kill me.

However, the two times I managed to defeat him, he went down like a mildly hostile sack of potatoes.