A forensic science technician may specialize in several, or just one, scientific field. Fore example, they may be a bullet expert, scene re-creation expert, tool-mark expert, bug expert, etc. The list really is very long. They may also sit in labs and rarely, if ever, travel to a crime scene. Depending on the circumstances, they may even be tasked with crime scene photography if. However; it has been my experience that often the investigator takes the photographs at the crime scene.
I have found a really good resource to be the Department of Labor Occupational Outlook Handbook. They do list and profile the outlook for a Forensic Science Technician as well as provide other information. It is a very in-demand job.
Here are the links in case the hyperlinks do not work:
DOL Handbook (many jobs profiled): https://www.bls.gov/ooh/a-z-index.htm#A