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William Optics GT71 f/5.9 Triplet Refractor

My last telescope purchase goes back to about 11 years when I upgraded from a beginner 130mm Newtonian to the 80ED bargain APO refractors launched by Syntha (Orion/Skywatcher) that everyone was raving about. I got one of the light metallic blue Skywatcher (SW80ED) and have been happy with its good optics and versatility for both visual and photographic use. Well actually, I upgraded the focuser as the stock unit didn’t do well with the weight of DSLR, often sliding out of focus or shifting when the tension was adjusted.

Over the past few years I’m been evaluating what should be my next move. From the 80ED there are many possibilities in the $800-$1200 CDN price range:

  • An 8in or 10in fast newton; a good bargain when it comes to pure light gathering power, and the fast ratio is great for photography. However collimation needs to be spot on, and will require frequent adjustments.
  • A 100-110mm doublet refractor will also gather more light and retain the easy of use like the 80ED.
  • Some entry-level catadiaoptric like Ritchey-Chrétien or Schmidt-Cassegrain are interesting with longer focal lengths for planets and galaxies

But with any of these options, the weight of the optic increases, and my current Vixen GP will start to struggle. Changing both telescope and mount was out of the question. I wanted something that could go well with my current gear. Hence a 70-80mm APO triplet started to look interesting, especially the small packages offered by some of the fast ones. After a week under dark skies without my telescope, I decided I needed something portable.  That’s when I jumped on an occasion to grab one of the star party demo units from William Optics: the Gran Turismo 71mm APO Triplet Refractor.

davIt may be a demo, but it looks brand new. Not a scratch on the powder-coat finished white optical tube or even the gold-colored dove-tail. Everything feels solid and the focuser looks like it can easily handle the heaviest DSLR. The SW80ED focuser is screwed to the back of the optical tub while the GT71 is one CNC machined unit, eliminating mis-alignment. As this is designed to be a travel scope, the soft-case that comes with it is very nice, much more portable than my current Orion hard-case. And at 2.2kgs, the weight is well within the range for the Vixen GP mount.

To compare the size, I’ve set it up next to my SW80ED, where it comes to almost half its length. The 80ED shares the same tube as the 100mm version, hence it’s bigger than it needs to be and the dew shield does not retract. Overall, the GT71 is more compact and will pack just about the same viewing power as the SW80ED.

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Below is a view of the optics.  While the SW80ED only has about 5 baffles within the tube, the GT71 has a good 30 of them to keep any stray light from ruining the view.  While both use FPL-53 glass, the SW80ED only has it in the rear element, while the GT71 is used for all three optical elements.  The SW80ED provides views free of chromatic aberration, however it’s designed to perform well in the blue and green part of the spectrum.  Anything is the deep red was falling out of focus, especially if a focal reducer was used.  The GT71 will perform better over a wide range of spectrum.

dav

I didn’t travel with my SW80ED, but now with a more compact telescope, I’ll be inclined to simply grab it during for my outings.  I just now need a light alt-az tripod to go with it.

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