A projection system comprises a light source module and a light-guiding assembly. The light source module comprises a reflecting cover and a light source disposed in the reflecting cover to form a first beam with a first f-number. The light-guiding assembly comprises a body with an incident end and a lens disposed on the incident end. The first beam passes through the lens disposed on the incident end to form a second beam with a second f-number. The second f-number of the second beam is different from the first f-number of the first beam.