Yes, the set of all sets is a logical contradiction because no set can contain itself, but would have to, if it is to truly be the set of all sets. In other words, there is no such thing as the set of all sets. It's logically contradictory and logically impossible, as you've shown. However, I'm utterly unconvinced of your claim that you can imagine the set of all sets. Such a set would have to include an Absolute Infinitely large set within it.
Yet, Absolute Infinity can never be contained (even in the imagination). There's no possible way that you have the ability to imagine a container of a truly infinite set. Therefore, there's no possible way to imagine the set of all sets.