It's not accurate to say Hubble focused on one specific nebula. The Hubble Space Telescope has been observing countless celestial objects throughout its lifetime, including many different nebulae. Some of the most famous and iconic nebulae observed by Hubble include:

* The Pillars of Creation: Located in the Eagle Nebula (M16), these iconic pillars are massive columns of gas and dust where stars are born.

* The Crab Nebula: The remnants of a supernova explosion, this nebula is a popular target for Hubble due to its intricate structure and rapidly expanding gas.

* The Orion Nebula: A massive star-forming region visible to the naked eye, Hubble has captured stunning images of the nebula's vibrant colors and young stars.

* The Ring Nebula: This planetary nebula, a shell of gas ejected from a dying star, showcases the intricate patterns and colors of such objects.

Hubble has also observed many other types of nebulae, such as supernova remnants, planetary nebulae, and reflection nebulae. It continues to provide us with breathtaking views of the universe and helps us understand the processes of star formation and evolution.