AR 102 Refractor review.
By Haseeb Modi.
AR 102 the Scope:
Astronomy is a hobby that keeps growing while making you feel younger. Sounds strange but this is a fact.
Consider this. The average age of an Astronomer is around 35 yrs, give or take a few. That would mean, amateur astronomers, ranging from ages 12 - 70 yrs. I know for certain there are amateur astronomers who are well within striking distance of a century.
Now coming to the point, owning a Dobsonian and SCT is fun and continues to be so. However, after reading so much about how a Refractor provides wide-field, rich contrasty views, the insatiable appetite for yet another fling at an instrument was on the cards.
Fortunately, I had a cousin of mine coming down from the States and he was kind enough to accept my request and get me an achromat, i.e., Explore Scientific's AR 102. First off, this was the cheapest option I could see, and second, Explore Scientific has a good reputation. Besides, I wanted to see what exactly were these wide-field views of a Refractor and lastly, the saddle plate is universally adaptable.
When the scope arrived, I found to my chagrin, the Diagonal was missing. I got this later on with my cousin's help ( I really appreciate all that he did ). The finish was white with a protruding longish dew shield. The paint was high quality and the components were sturdy. The focuser seemed quite smooth and strong enough to hold a 2" diagonal with a heavy eyepiece or camera. The only issue I had was when the focuser got stuck by the adhesive used on the plastic markings which I had to get rid off. Minor issues aside, the feel was solid. The straight-through 8 x 50 finder was adequate for the purpose and aligning to the scope during daytime was easy enough. Some may think the Finderscope looks misaligned mounted on the scope and indeed that would be one's perception when seeing the scope in its entirety. However, it works and that's that.
The baffling is good enough and the coatings are great. The dew shield ( I always keep it extended ) helps protect the lens from the forces. There are six small collimating screws but the scope came well collimated out of the factory and the star test showed concentric circles both inward and outward focus.
FIRST LIGHT:
This air-spaced doublet has a 663 focal length and f/6.5 focal ratio. It is relatively large with a diameter of 102mm or 4". The highest useful magnification is stated at 220X. I never had a chance to go that high but I did push the scope up to 200X by using an ES 6.7mm 82 degrees eyepiece with a Barlow inserted. Saturn at 200X was completely in focus. A fine focus ring helps in making micro corrections.
Normal views through this Achromat are quite pleasing with only the brightest of objects showing hints of CA or Chromatic Aberration or purple fringing.
What is surprising is the fact that even in extremely light polluted conditions, viewing from within a large city, I was able to see M 31, M 13, M 57, and other Globular clusters. Only faint galaxies or galaxies with less surface brightness would be difficult to find but that is something even an 8" Dobsonian may find difficult to obtain from light-polluted cities. Of course, even an 80mm Refractor will give you pristine views of fainter galaxies provided one takes a trip to the outskirts or to areas with less light pollution.
The Moon and Planets however are excellent to look at. What really stands out in all its beauty viewing from this Achromat Refractor are the Open clusters. Being in the Southern region, we are blessed with the Sagittarius area which forms the bulge of our Milky Way and thousands of stars are visible through the scope even from light-polluted cities. Just ensure the nights are clear with little to no clouds and try to shield your eyes and scope from stray light or neighbors lights.
ASTROPHOTOGRAPHY:
Now an Achromat or a normal doublet is not the ideal choice for imaging. But one has to make do with resources available and none better than an F/6.5 with a short focal length to try my hand at imaging some galaxies. This scope performed within expectations but the purple fringing or purple halos around brighter stars are prominent. Here's an example:
I had to process this image vigorously to remove the "purple fringing" but could do nothing about reducing star size. In fact, this image is after using Noel Carboni's star tools and star reduction and purple halo reduction around stars. But the image is pretty and more than can be expected with minimal equipment, imaging from inside a light bowl.
Bear in mind though, there are other Doublets with Extra Dispersion or ED glass and with even 65mm aperture, which can make for excellent astrophotography equipment. Their short focal lengths and the focal ratio will help in snaring galaxies, even fainter ones. Only be prepared to take as many "light frames" or "Subs" as possible to stack them later to obtain signal-to-noise reduction as well as enough photons to bring out detail.
( Disclaimer: This review is purely based on my own reading and from my own perspective of AR 102 and I have not affiliated in any way with Explore Scientific ).
Haseeb Modi.
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