Dew Prevention and Removal

In order to know how to combat dew, it is important to have some understanding of why it forms. Water vapor condenses out of the air onto any surface and simultaneously evaporates from that surface. The potential rate of evaporation is lower at lower temperatures. Below a specific temperature, the dew point, the rate of evaporation is lower than the rate of condensation and dew forms. The principles of dew reduction are then simple reduce the amount of cooling of the optical surfaces and reduce...

Handheld Binoculars

Hand-held binoculars are the choice for extreme portability, casual observing, and as a preliminary sky-scanner used in conjunction with a larger instrument. Almost all binoculars, including cheap plastic opera glasses, will show you more than the naked eye, but a sensible lower limit of aperture for portable astronomical binoculars is 30 mm. If extreme portability is not an issue, 40 mm is significantly better as it will admit more than 75 percent more light. As aperture increases, so does the...

Binoviewers

Binoviewers are designed to permit the use of two eyes with a single optical tube assembly Figures 3.9 and 3.10 . The rationale for their use is that they offer some of the advantages of binoculars with few attendant disadvantages. The obvious advantages are the reduction in eye strain from using two eyes, the suppression of the blind spot, and the aesthetics of false stereopsis see Chapter 1 . The obvious disadvantage is the loss of light into each eye that results from the splitting of the...

Prisms

Pechan Roof Prism Binoculars

The prisms in binoculars serve primarily to correct the inverted and laterally reversed image that would otherwise result from the objective and eyepiece alone. A secondary effect is that they fold the light path, so that the binocular is shorter than it would otherwise be, making it easier to handle. As stated above, binoculars are often classified according to their prism type. For modern binoculars without angled eyepieces, there are two basic types the Porro prism and the roof prism. Figure...