### 6.10.4 Photon Tips

- Use `collect off` in objects that photons do not hit. Just put `photons { collect off }` in the object’s definition.
- Use `collect off` in glass objects.
- Use `autostop` unless it causes problems.
- A big tip is to make sure that all of the final densities of photons are of the same general magnitude. You do not want spots with really high density photons and another area with really low density photons. You will always have some variation (which is a good thing), but having really big differences in photon density is what causes some scenes to take many hours to render.