Optical diagnostics are widely used both for experiments of plasma physics and for measurements of parameters of electron/positron beams in accelerators. The approaches, applied for that, often have the same methodological basement that is explained by similarity of properties of the studied phenomena. Nevertheless, these branches of physics are very specific and require special diagnostics. Possibility of closed contacts and cooperation between scientists solving similar problems at different areas of physics helps to overcome these problems. It is especially typical for BINP SB RAS known by pioneering works on electron-positron colliders and nuclear fusion. The paper describes the diagnostics that are used at the experiments of plasma physics, especially for plasma heating by high-current electron beam and contains comparison with optical diagnostics which are recognized tools at colliders and storage rings.