Skywatcher ED-100 pt2

By Antony McEwan

Further Viewings

The ‘scope has seen a lot of use since then, including star party viewing sessions at Culloden, dark site sessions, and quick peeks from my garden. Viewing highlights that spring to mind include seeing the 5th ‘E’ star in the trapezium on a night of excellent seeing, sharp detail and subtle colours on Saturn, including the shadow of the planet on the rings, and tonal variation at different latitudes on the globe. It also shows open clusters beautifully, and is able to give wide fields of view when using 2” eyepieces, which show objects such as the Beehive cluster, Double cluster, Pleiades, Hyades and open clusters of Auriga as sprinklings of sharp pinpoint stars against an ebony background. Truly the way open clusters are meant to be viewed!

On one occasion I tried for some galaxies with the ED-100, and was very pleased indeed with its performance in showing the pair of galaxies M81 and M82 in Ursa Major. I was using a Moonfish 30mm 80 degree eyepiece that night, and while it didn’t show anywhere near the level of detail my 8” Dobsonian shows, the view was very pleasant and it was obvious what the target was. Of course, swinging that combination over to M42, the Great Orion Nebula, left me gazing in wonder at the panoramic view. Visible were the swirls of nebulosity; the sharp stars of the trapezium in the middle of the star-forming cloud of gas and dust, and the strands and wisps that spread out from them, shaping themselves into wing-like structures that nearly filled the field of view. Adding a 2” Ultra High Contrast filter increased the contrast of the nebulous areas against the background sky, but did dim the stars quite significantly.

I star-tested the ‘scope quite early on, by lining up on medium bright star, and racking the focus in and out while using high magnification (240x). The diffraction rings at this magnification were completely circular in focus, and when defocused the ring around the star stayed perfectly circular, showing that the optical alignment of lens and focuser was perfect. My very limited understanding of what the star-test shows suggests that the telescope has a good pair of lenses, as the rings seemed evenly illuminated around their circumferences, and on a night of very good seeing there seemed to be no distortions within the solid circle of light when the image was defocused to the extent where the rings filled a large part of the field of view. Star-testing isn’t my forte, but this result, in combination with the fact that everything I’ve looked at through the ED-100 looks exactly as I would expect it to, seems to suggest to me that the optics are good, or possibly very good.

On the subject of false colour, I have to say that the views are not as colour free as those shown by my reflectors, but they are very close to it. The views are not spoiled at all by blue fringes around bright stars and planets, but it is important to have the image perfectly focused to get the best out of the optics. Lunar views are very nice indeed, with stark black crater shadows, and only the tiniest hint of blue-green shown at the full moon’s limb, similar really to what my TeleVue 85 shows under similar circumstances. In short, I had to really look for it. I have read other reviews where owners have stated that compared with much more expensive Apo’s, the ED-100 provides 90% of the performance at 25% of the price. I agree with this, and so I think that it is definitely worth the asking price, and does add something to my collection of telescopes. Three somethings, actually: versatility, portability and performance.

Mechanicals

The ED-100 performed very well, and gave a suitably high smile-per-view ratio, but there were some things about it which I became aware of that would need to be ‘fixed up’. First is that the ‘Visual Back’ or accessory ring that attaches the diagonal to the drawtube uses two very small, light screws to hold the diagonal in place. This does not make for the most secure fastening, especially when a good diagonal and eyepiece combination can weigh up to a pound and a half! Also, these screws can scratch the barrel of the diagonal (this is only a cosmetic issue) but I was not too happy about the risk of one of the screws working loose in the cold and the diagonal and eyepiece rotating, or even dropping out. The solution is to remove the supplied adapter and attach a third party one that uses a compression ring to hold the diagonal securely in place. I ordered one from Mercury Systems in the USA, and this is a much more secure option. They are also quite inexpensive at about $37 US each (about £20 at the time). The difference was immediately noticeable, and I was much more confident when using heavy eyepieces thereafter.

The Crayford focuser was very nice to use, but I found that when pointing the telescope upwards there was a tendency for the drawtube to slip under some conditions, making it harder to rack the drawtube ‘in’ towards the objective. The recommended solution is to tighten the friction knob, which results in more pressure on the drawtube, meaning less likelihood of slippage. This worked, to a degree, but I found that I had to tighten the knob quite a bit to eliminate the slip completely, and that by doing so the tension on the focuser was a little more than I liked. It’s a tricky thing to describe, and a subtle effect, but I found that it was a little niggle in the back of my mind. The motion of the focuser is actually very good indeed, and it is easy to find the focus sweet spot most of the time. Having said that, there was one occasion when the drawtube actually slipped out quite quickly, and would have caught my face if my reactions hadn’t been quick enough. I then resolved to tighten the friction knob up and leave it tight forever more, and just put up with the slightly increased tension. It’s really not a big thing, just a minor point to be aware of.

Those are the only slightly negative points I found when using the ‘scope on many occasions, and I consider that to be quite a good record, especially for a telescope in this price bracket and with so much to prove.

Minutia

I should mention some other conclusions drawn from my months of use of this ‘Budget Apo’. First off, it’s been great fun to use. It’s very quick and easy to set up, and takes only a few minutes to cool down to ambient temperature, even on nights of -5’C or so. Also, it is easily mounted, and was just as at home on my Giro II alt-azimuth mount as on the Vixen GP. It is the first telescope that I’ve taken photographs through. I captured some shots of the Moon, and the close conjunction of Mars by the Moon using my Nikon Coolpix digital camera. This was something completely new for me, but the camera did most of the work! The images were processed using Photoshop Elements, and can be seen on the Spacegazer Image Gallery. I have just been examining the unprocessed images to see the extent of false colour at the limb of the Moon, and it is barely evident at all. I still have these original images if anybody wants to check them for themselves.

I also use only good quality eyepieces with my telescopes. The eyepieces used during the viewing periods included TeleVue Plossls, Pentax XL’s and standard Orthoscopics. For ultra wide-field my Moonfish 30mm 80 degree eyepiece was used, and for the afocal projection for the Moon images a Meade S4000 32mm Plossl. All the eyepieces reached focus easily with no need of any additional tele-extenders or adapters of any kind.

Conclusions

I like this telescope. It does show a ‘little bit more’ than the TeleVue85, and has colour correction that is almost as good as the pricier brand leader. The 2” focuser is very good once I grew accustomed to its foibles, and the wide field views offered by it are excellent. It zooms in well for high power viewing, and maintains a bright image up to reasonably high power (~200x for the gas giants is quite usable, and more for lunar features).

And then there’s the value for money. The telescope itself cost me just under £500, and I have to add to that £100 for a high quality diagonal and £70 for the optional aluminium foam-lined case. Tube rings and a dovetail plate were included in the price. The visual back adapter cost me another £20, bringing my total outlay to £690. To buy any other brand of 4” Apo would cost me at least twice that, and probably more. The telescope has delivered images that met my expectations with regard to optical quality and colour correction. I have to describe this as a bargain. Maybe I was lucky to get one in such fine optical shape, or maybe all Skywatcher ED-100 Pro tubes are as good as mine. Or here’s a thought- maybe there are some out there that are even better…!

So I am one totally happy ED-100 Pro owner. So much so that I have taken steps to remedy the only weak link in my particular example- the slightly loose focuser travel – by ordering a replacement third party alternative model focuser. I didn’t do this lightly, and I realise that many people will not be bothered to the same degree by the ‘problem’. I just feel that the optics, and the telescope in general, are so good that they easily justify the additional £100 expense of a high quality up-market replacement focuser, especially as I intend to keep (and use) it for quite a while! Details of fitting and using the replacement focuser will follow in an update to this review, but for now you can safely say I think this ‘scope is great!

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