by The Bolton Group
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200 mm (8 inch) Binoculars
by The Bolton Group
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 Assembling the Binoculars |
These binoculars were made by Gerald Bramall to his own design in polished aluminium with twin 200mm f6 mirrors. They are altazimuth mounted and hold collimation perfectly. They perform as good as they look! New 26mm plossl eyepieces have recently been fitted and they provide stunning deep sky views from our dark site in the Lake District. Until you have tried two eyes words cannot describe the experience they provide. It's as if there was no telescope there and you were actually out in space!
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 User's eye view |
The tubes use the same technique as the 16 inch, ie diaphragms and tubes with through threaded rod and bolts. Unlike the 16 inch the top section, comprising three diaphragms, separates for transportation. The binoculars are currently being modified so that they can be collimated single-handed by having mirror cell adjusters in reach from the eyepieces.
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 Close-up of eyepieces |
To set them up, first the inter-ocular distance (ie for the distance between your eyes) is adjusted by means of crayford type focusers. The actual focusing is individual and helical. However, we have discovered for collimation that it best to aim at a bright star and defocus one telescope. The reason for this is that if the two images are the same, the brain will snap them together long before perfect collimation is achieved. By defocusing one image, this is prevented and the two telescopes can be perfectly aligned.
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