If Superman can turn off Manchester Black's powers, can he focus his heat vision to a microscopic level?
Apparently he can. During the Superman vs. the Elite storyline, the powerful mentalist Manchester Black, actually put Superman on the ropes. In a move rarely seen by Superman, after taking much abuse from the Elite, he turned off Manchester Black's powers using his microscopic vision in conjunction with his heat vision acting as a laser scalpel inside of Black's brain.
Through the optic nerve Superman basically lobotomizes Black, using his heat vision, invisibly, to remove Black's access to the source of his incredible mental powers.
Apparently, Black's powers existed as part of a malformation, perhaps cancerous, which activated his mental abilities.
Black was a skilled telekinetic and telepath who was capable of very precise uses of telekinesis. He was, for example, able to give Superman the equivalent of a stroke by telekinetically pinching the blood vessels in Superman's brain. He can also emit offensive blasts and erect shields over himself and others.
Black was also able to create very detailed illusions on a vast scale, and could telepathically control thousands of minds at the same time. While controlling Bizarro and Silver Banshee, he was able to temporarily grant them enough sanity to enable them to communicate and to form plans. He was also able to switch Superman's and Bizarro's minds, putting their consciousnesses into each other's bodies.
Given Black's disregard for the rights of others, his blatant misuse of his powers, and his willingness to murder criminals rather than arrest them, Superman felt justified in removing Black's abilities as an opportunity to protect the Greater Good.
But for those of of you who want to know if he can use his heat vision with microscopic effects beyond surgery and with greater power levels, behold:
- Superman using his heat vision to penetrate a force field prison whose capacities indicated it exhibited the same properties as a black hole, having an inescapable event horizon.
- Superman will be using said heat vision to create recreate the heat event where spacetime begins to generate sufficient virtual particles that some will appear on the other side of the field, allowing his heat vision to penetrate and disrupt the field. This should take temperatures into the millions of degrees focused on a tiny point.
- He will use his heat vision at million degree temperatures on a microscopic level to penetrate the force field and NOT fry Batman and Robin who are inside the force field with Superman. A delicate, microscopic but powerful use of his heat vision in a highly unusual circumstance.
In Superman: Son of Kal-El #11, Jon Kent demonstrates that he has that ability when he disables a brain implant that was about to kill the unwilling supervillain Inferno:
As for the OG Superman, Clark was called into perform emergency surgery on Power Girl to save her life in Justice League Europe #9 when she was unable to be treated by mundane medical technology due to her superhuman physiology. In this case, it was a combination of his microscopic vision, heat vision, and technological assistance.
There was a pre-Crisis story in which Jimmy Olsen accidentally discovered Superman's secret identity but was worried that the information might be tortured out of him by criminals. Superman therefore used a combination of heat and microscopic visions to burn out the relevant part of Jimmy's brain. However to avoid this being used as a convenient get-out in the future, Superman specifically said that he could never do it again for fear of short-circuiting his vision powers.