27 May 2020

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  • Until comparatively recently, if you wanted to capture extended deep-sky objects such as diffuse emission nebulae and supernova remnants with your full-frame DSLR or CCD/CMOS camera, then your best option was to invest in an f/2 or f/2.8 telephoto prime lens from one of the big-name players in photography. Such high-precision solutions possess multi-element lenses, often made of exotic glass, and sometimes with aspheric shapes designed to ensure tight control of false colour, off-axis aberrations and field curvature over a large imaging sensor. Not surprisingly, lenses possessing these desirable characteristics don’t come cheap. For example, a Nikon 200mm, f/2 G ED AF-S Nikkor VR II or Canon EF 200mm, f/2 L IS USM will each lighten your bank balance by more than £5,000. While f/2 and f/2.8 prime lenses can record bright nebulae and galaxies in minute-long exposures at the high ISO sensitivities of modern DSLRs, 200 and 300mm focal-length lenses are too short to reveal fine detail in small-scale examples of these deep-sky objects, unless one is prepared to use one of the new breed of cameras employing CMOS sensors with tiny (less than 2.5 micron) pixels. Even so, most astro-imagers would prefer focal lengths of at least 400 to 500mm to ensure optimal pixel sampling, at which point one balks at the astronomical cost of prime camera lenses meeting those specifications. Fortunately, there are catadioptric – that is, optical instruments employing both lenses and mirrors to form an image – alternatives that are much cheaper, one of which is the 150mm aperture, 420mm focal length, f/2.8 SharpStar hyperboloid Newtonian profiled here. Delivery and first impressions It’s a truism that you never get a second chance at a first impression, but few will forget the first time they set eyes on the SharpStar D 150mm, f/2.8 HNT, hereafter called the HNT

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