Big Guns

  • Neil English
Part of the Patrick Moore's Practical Astronomy Series book series (PATRICKMOORE)


A 6-in. F/8 scope is quite manageable, but how does a 6-in. F/15 instrument grab you? The issue with an F/15 scope is not so much its heaviness as its sheer unwieldiness, like a giant pencil turned on the sky. Such an instrument requires a very beefy mount, and it’s got to be raised quite high off the ground so that you can comfortably look through it, especially when pointed high overhead. The reward for such effort is exquisite images, perfectly corrected for all of the aberrations that can plague a refractor and almost devoid of false color. For some enthusiasts, super-long focus achromats provide the best planetary images of any telescope, period. They are adored by refractor fans the world over. The Pennsylvania-based company D&G Optical gives you a real taste of this refractor high life. Founded in 1987, the company is dedicated to providing some of the finest achromatic doublet objectives – either as lens cells or fully assembled optical tubes – to the discerning amateur astronomer. The D&G lenses range in size from 5 to 12 in. with large focal ratios ranging from F/12 to F/30. So, even a 5-in. is a monster! Due to their gentler curves, long focal length lenses are easier to make well, but the extra time dedicated to them by a master optician can result in an objective that can take stupendously high magnifications – as much as 100× per inch of aperture. The company takes pride in the fact that its objectives are not mass produced. Each lens is individually hand figured, and each is guaranteed to reach the theoretical limit of resolution for its size. All lenses are fully coated to increase light transmission and are color corrected for the C-F visual range between 500 and 650 nm. These giant eyes on the sky have a singular ability to invoke the halcyon days of the nineteenth century, when the great visual observers mapped and measured the heavens.


Spherical Aberration False Color Focal Length Lens Double Star Lens Cell 
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Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  1. 1.GlasgowUK

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