I have only one day to visit outskirt of London, I would like to visit Oxford mainly to take some photos of the great dining hall in the Christ Church college for my son who is a Harry Potter die-hard fan. I wish to visit Winsor Castle myself, but I don't know if one day is enough to visit both places, not in depth, but just to get out of London and take a peak of the Royal residence
I don't really see the point of going to Oxford just to take photos for somebody else - if your son was with you fair enough, but since he's not I think you'd be better off saving Oxford for a trip with him in tow and focusing on Windsor.
I say go to Windsor, tour the castle and walk around the town. I'd leave Oxford for another time. I think your son can visit for himself one day. Too much rushing around otherwise.
My 2 cents!
Hi one important factor to consider is that whilst it is only 45 miles from Windsor to Oxford, this could take 1 1/2 hours plus to travel and parking in Oxford town center or even driving into it will be difficult. You may well struggle to do both any justice in one day
I vote for Windsor and enjoy a leisurely day rather than trying to rush from place to place.
You can't visit any of the colleges, when they are in session. Go for Windsor Castle instead.