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 light into two optical paths and from the additional optical elements in each light path. While binocular summation (see Chapter 1) can compensate for some of this loss, the overall perception is that using a binoviewer is equivalent to a loss of about one third of the illumination as compared to a single eyepiece. In addition, the cost of providing matching eyepiece pairs, thus doubling the number of eyepieces required when compared to a conventional telescope, is not one that can be ignored, especially where good quality eyepieces are used. However, this is ameliorated to some extent by the development of binoviewers that incorporate the facility of multiple magnifications without changing eyepieces.

An advantage that is not common to conventional binoculars is the ability to use high magnifications without the need to collimate two optical tubes. Another is that their use with telescopes of large aperture provides an equivalent aperture that would be significantly more expensive and technologically difficult to achieve with binoculars or binocular telescopes. A less obvious advantage when they are used at high power concerns "floaters." Floaters are strands of protein that float within the transparent humors of the eye and become apparent, sometimes dis-tractingly so, when one is observing with a small exit pupil. Users of binoviewers

Figure 3.9.

Denkmeier binoviewer used with a limited edition 12.5-inch f/6 Teeter's Telescopes "Planet-Killer" telescope. (Photo: Copyright 2005, Teeter's Telescopes)

Figure 3.9.

Denkmeier binoviewer used with a limited edition 12.5-inch f/6 Teeter's Telescopes "Planet-Killer" telescope. (Photo: Copyright 2005, Teeter's Telescopes)

Figure 3.10.

Celestron binoviewer attached to a Meade 10" LX50. (Photo:

courtesy of Gordon Nason)

Figure 3.10.

Celestron binoviewer attached to a Meade 10" LX50. (Photo:

courtesy of Gordon Nason)

report that their visibility is suppressed, often to the point of elimination, probably in the same way as they suppress the blind spot (page 3).

If you are considering a binoviewer, you should ascertain its clear aperture, as this will place a limit on the lowest power of eyepiece that you can use effectively. In cheaper units this can be as little as 20 mm, restricting the eyepieces to those with a field stop less than or equal to this. You should also ascertain whether your telescope has sufficient back focus to permit it to be used with a binoviewer; a Barlow lens in the "nose" of the binoviewer may enable this. Finally, you should consider those that have self-centering eyepiece holders as this will eliminate any miscollimation that may otherwise result from slightly undersized eyepiece barrels being held off-center by thumbscrews.

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Responses

  • myrtle
    What is the lowest power eyepiece i can use with a celestron binoviewer?
    8 years ago

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