Sky-Watcher EvoStar 80ED Refractor Telescope

Sky-Watcher 80ED on Celestron GT mount

This is my third 80mm scope — the first was a Sky-Watcher StarTravel 80 and the second was a William Optics ZenithStar 80 Short. Those two were achromatic refractors, which means they show some false colour on bright objects at high magnification. The 80ED is an apochromatic refractor; one of the elements in its doublet lens is made of a glass that contains fluorite, which allows the scope to have much less chromatic aberration.

The photograph shows the scope mounted on my NexStar 80 GT mount, via a Baader adapter that allows the mount to be used with any small scope. At 8½lbs (including accessories) the ED80 is a bit too large and heavy for this mount, and use at high magnification is impractical. However, it is a lot quicker to set up than my EQ-6.

I bought the scope in October 2006. At this time there was a wide variety of 80mm apochromatic refractors to choose from. I was very tempted by the William Optics ZenithStar 80 II ED, but chose the Sky-Watcher as it has a proven track record in astrophotography. It is not as "well engineered" (i.e. heavy) as the William Optics scope, but it is much more amenable to being upgraded and tinkered with. Improving a basic scope is unlikely to be cost effective compared to buying a better scope up front, but I enjoy doing it.

William Optics focuser fitted to ED80

The first upgrade I've done is to replace the stock focuser with a William Optics 2" focuser for Synta refractors. Unlike the Baader focuser I fitted to my 6" f/5 refractor, this has a 10:1 slow motion knob which makes fine focusing very easy. The focuser is really easy to fit. Simply unscrew three retaining screws, pull out the old focuser, insert the new one and refit the screws. Unfortunately the new focuser has a slightly smaller flange than on the stock focuser (96mm instead of 97mm) so tightening the screws pulls the scope tube slightly out of shape. I've cured this by using strips of self adhesive canvas tape to increase the diameter of the focuser flange. I was able to sell the virtually unused stock focuser to another astronomer for £50, making the upgrade a little bit more cost effective.

Just visible in the photograph is a millimetre scale I've added to the focuser drawtube. I made this by drawing a suitable scale with xfig, printing it onto plain white paper, cutting it to size and sticking it to the drawtube with double sided tape.

The William Optics focuser has almost exactly the same travel as the original, yet its drawtube is about 40mm shorter. The original's drawtube also has two baffles. I didn't check for vignetting before changing the focuser, but if the original focuser drawtube was causing any problems they're gone now!

Sky-Watcher ED80 in its case

I bought the scope with its purpose built aluminium case. I'm fed up with keeping my scopes in cardboard boxes and have decided to get nice cases for all of them. The Sky-Watcher case is basic, but perfectly adequate. It is lined with some fairly stiff but low density foam which I've found is easy to cut with a modeling knife if a compartment needs to be enlarged.

As well as replacing the scope's focuser, I've mounted its tube rings on a William Optics dovetail plate, so the scope can be mounted directly on my modified EQ-6. I've had to cut out quite a lot of the case's foam to make room for these extras, but the scope does still fit.

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