This book is about using an 80mm refractor / 90mm Maksutov (such as a Helios 80 or Meade ETX90) as more than a 'quick look' instrument, but rather something capable of use as an introduction to scientific observations. Emphasis is on measurement and discovery activities rather than on casual observing. There are two objectives to these activities: to re-enact the process of discovery and to provide amateur observers with the knowledge and skill that will help them make genuine contributions to the field of astronomy. It is often said that users of small telescopes can conduct worthwhile scientific work, but how is seldom explained except in the context of observations carried out by the most advanced amateur astronomers. This book provides the necessary introduction derived from the authors many year of experience in teaching the subject that will be the starting point for serious work. Users will find many activities and projects suitable for an 80mm refractor or 90mm reflector or Maksutov that have not been published elsewhere.