The above images of galaxy cluster SMACS 0723 (located 4.6 billion light years away) highlights the huge resolution jump from Hubble to Webb.
Webb’s first full colour image took just 12.5 hours of integration time to capture and already reveals detail surpassing Hubble’s deepest field images, some of which took weeks of accumulated processing time.
The area of space imaged in this composite is equivalent to holding a grain of sand to the night sky at arms length. Almost all the individual points of light here are separate and independent galaxies, each containing 100s of billions of stars, and captured in various stages of historical morphology going back as far as 13 billion years (due to the help of gravitational lensing).
While greater mirror diameter and enhanced sensor resolution accounts for much of the extra clarity Webb has over Hubble, it should be remembered that James Webb is an Infrared telescope, so less detail in its deep field images gets obscured by opaque interstellar dust, which can block some of the visible wavelengths of light Hubble sees. Also, visible light that has experienced extreme red shifts (due to the expansion of the universe) can end up stretched into the Infrared, so Webb can look much further back in time than Hubble, revealing some of the oldest first generation galaxies yet seen.