Field and Bench Testing

Unless we state otherwise, the numbers presented in S&T Test Report are determined by us and are not just a rehash of specifications provided by the manufacturer or distributor. This goes for everything from the size and weight of a telescope to the aperture, focal length, and central obstruction of the optical system.

Anyone can hold a ruler up to the primary mirror of a Newtonian reflector, but this may not give a true indication of the telescope's effective aperture. Measuring the true light-gathering power of a refractor or catadioptric system is even more problematic. In all cases we measure optical parameters using carefully controlled tests. We determine the diameter of the aperture that collects and focuses starlight to a point on the telescope's optical axis. And we measure a telescope's effective focal length from the image scale at the focal plane with the instrument focused at infinity.

Most experienced observers can develop an informed opinion of a telescope their first night under the stars. This is certainly true of our reviewers, who on average have been amateur astronomers for more than 30 years each. But we go much further than one or two nights of field-testing. We typically spend four to eight weeks evaluating equipment before writing about it. We drag scopes in and out of garages and spare bedrooms, pack them in cars and drive them to star parties and dark-sky sites, and sometimes leave them covered outside for days at a time. We share views with family and friends as well as with other experienced observers. In short, we test telescopes under conditions very similar to those experienced by our readers.

As such we can make an accurate assessment of how a telescope performs in everyday use, uncovering issues overlooked during the first night or two of testing, while dismissing others that initially seemed like potential problems but proved not to be in the end. We are particularly proud of this kind of field-testing, and we consider it at least as important as our bench testing.