Premium APO, Moderate Price: SharpStar 140PH APO Triplet

The Sharpstar 140PH apo dew cap extends 5 inches out from the objective. With the dew cap retracted the tube is 30.5 inches (77.5 cm) long. The rings include a wide Losmandy-standard plate and a slotted carrying handle. Credit: Alan Dyer

A new big-aperture refractor providing top-class optical and mechanical performance to appeal to apo aficionados.

Plus:   Excellent optics and mechanics; suitable for both visual and photographic use

Minus: Heavy, though solidly built; some vignetting with optional reducer/flattener

Summary: The SharpStar 140PH is a superb large-aperture triplet apo at an attractive price given its high-end performance.

Who Is It For? Aficionados of premium optics looking for a first-class apo without the extreme prices and wait times of some competing brands.

No telescope carries more prestige — and price per inch of aperture! — than a large apochromatic refractor. While smaller “apos” can be affordable, only those who prize the sharp, high-contrast images of this design can justify the expense of an apo over 100mm aperture.

The SharpStar brand from China is a new entry to the apo market, with models at attractive prices . The company has made telescopes sold under other brands, but it is now offering telescopes under their own SharpStar name.

With samples supplied on loan by All-StarTelescope.com, the Canadian dealer for SharpStar, I tested SharpStar’s smaller 76mmEDPH triplet and 100mm quadruplet astrograph, and was very impressed. But for those who want aperture, the 140PH is the largest refractor in the SharpStar line, with a 140mm f/6.5 triplet lens featuring two elements made of unspecified ED glass.

Refractors this large can be prone to optical issues caused during lens manufacturing and mounting, so I was pleased to see no aberrations or flaws that would take this telescope out of the first-class league. Color correction was as good as I have seen with other premium apos, and I have owned and used the best. On cold nights there was no astigmatism from pinched cells. In-focus stars presented near textbook-perfect Airy disks. The only visible flaw was a trace of spherical aberration in extra-focal star images.

The 140’s entire focuser rotates, and includes a rear camera angle adjuster. The focuser’s M88 threads accept the included step-down ring, which in turn receives the 2-inch visual back. Credit: Alan Dyer

The focuser is a massive 4-inch rack-and-pinion with a smooth and precise 10:1 dual speed adjustment. It racks out over a generous 110mm range and locks securely. The entire focuser can rotate, while the back end has a lockable camera angle rotator as well. A dovetail bracket on the focuser accepts a user-supplied finderscope. The telescope comes with a solid traveling case, but does not include a star diagonal or finderscope. The 140PH delivers superb views with its 5.5-inch aperture, just shy of much costlier 150mm (6-inch) apos.

A raw unprocessed image taken in moonlight shows the level of vignetting with the optional reducer/flattener (above) and, in the closeup (below), the excellent correction of aberrations out to all but the extreme corners of a full-frame sensor. Credit: Alan Dyer

Photographically, at its native f/6.5 and 910mm focal length the 140PH provides a flat field over the central 25mm of a full-frame (24x36mm) sensor, more than enough for use as is with smaller sensor cameras.

For a better corrected field, the optional three-element 140PH reducer/flattener provides a faster f/4.8 focal ratio and an effective focal length of 670mm, providing a field flat to the corners of a full-frame sensor. Light fall-off at the corners was one f-stop, which isn’t bad, though I would have expected better field illumination considering the size of the reducer/flattener.

The SharpStar 140PH is an impressive visual and photographic apo with an attractive price for its aperture and performance. If I didn’t already own a premium 130mm apo, I’d be tempted!

MSRP:
SharpStar 140mm triplet apo refractor: $4500
Optional Reducer/Flattener: $400

Website: http://www.sharpstar-optics.com

About Alan Dyer

Alan Dyer is an astrophotographer and astronomy author based in Alberta, Canada. His website at www.amazingsky.com has galleries of his images, plus links to his product review blog posts, video tutorials, and ebooks on astrophotography.

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