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Explore Scientific AR 102

Posted by Paul Temple   01/31/2016 12:00AM

Explore Scientific AR 102
As a guy with a robotic telescope that primarily does variable star photometry I actually miss looking through a telescope sometimes! Staring at a monitor from your warm house is a plus but as I get older I long to grab a scope let the photons roll into the Mark 1 eyeball! So a couple of months ago I began to think about a “grab and go” scope.

In my storage area was a 8” F/5 Astrograph that I no longer used. So I decided to sell it and use the proceeds to buy the “grab and go” scope. Luckily, I had a friend looking for this kind of scope and sold it to him. There is also a Celestron GT mount in the storage area that I have never used that would probably work as a mount for a light refractor. The remaining question was what to buy?

As a life-long astronomy buff I have a lot of telescopes. My first real scope was a 60mm Sears refractor. I used this for years until it got broken while I was cleaning gunk off of the lens. In my current “stable” of scopes is “ The Bargain Bucket” a 8” homemade F/5 Dobsonian, “Little Eye” a Meade ETX 90mm, “The Beast” a Celestron 6” F/8 refractor, Temple 28 a Celestron 11” CPC roboscope and a Meade LX200 8” roboscope. One of my favorite scopes is “ Dimestore,” my Meade 60mm, “junk” telescope. I got tired of listening to APO and ED Refractor users complaining about the venerable 60mm scopes so I bought one on EBay for 21 dollars delivered. I used it in it’s stock condition to view Mars at the last good opposition. I did a color sketch with watercolor pencils that got used in a montage of images from the Mars opposition and made one of the “image of the day” websites! After doing the sketch, I upgraded the focuser and use it for a “grab and go” scope. However, there’s just not enough aperture and though the Alt/Az mount is Ok, it could be better!

With $300 (US) to spend, my first thought was to buy the 72 mm ED from Astro Tech. All of the products that I have ever bought from them, including the 8” F/4 astrograph that was sold, have been great. The reviews on that scope were terrific, however, it just seemed to be a little on the small side. Though 72mm is way more scope than the 60 mm, I just wasn’t sure I wanted one that small, especially since it was over the budget by $75. Unfortunately, larger ED’s or APO’s were out of my price range. Just about everything else I looked at had some major flaw (bad focusers primarily) or was out of my price range. After perusing Astromart and seeing only one scope that I was interested in and it was over $450, I decided to check out slightly larger achromats. Better “bang” for the buck!

As mentioned earlier, “The Beast” is my 6” achromatic F/8 refractor that sits on a Sirius mount with a extension pier. Since it is over 100 pounds set up it is definitely not a “grab and go” scope! The optics are excellent though and the Chromatic Aberration is surprisingly well controlled for a scope like this. Plus, the Celestron Minus V filter (Same as the Baader Fringe Killer) does a good job on the CA and doesn’t change the color of the view much. With the experience of using “The Beast” I felt like a short Achromat would be a good telescope for me and even give me a bit more aperture for the money.

I looked at the High Point Scientific website to check out the AR series optical tube assembly from Explore Optics. These are nice looking scopes that come in 102mm, 127mm and 152mm diameter lenses and F/6.5 focal ratio. By the way I am not affiliated with HighPoint Scientific or Explore Scientific in any way! However, Highpoint has been extremely helpful in all my dealings with them. The 127 caught my attention first but the price was over my budget. Plus the weight and size seemed to be going the wrong way for a “grab and go” scope. So I began to seriously consider the AR 102.

Email was sent to Highpoint and they responded quickly with links to reviews. Most of the reviews praised the build, optical quality and size of the scope. There was not a negative review that I could find on the internet or in their links. That is very unusual for just about any product. The only negative was the CA inherent in the short focal ratio but every review commented that it was not as bad as expected, nor did it hinder the quality of the views. So I pulled the trigger and ordered the scope. Did I mention that it went on sale a day or so before I ordered it? Did I also mention that I got an open box unit for a 30 dollar discount under the already lowered price of $299 US. It also came with a 25mm, 70 degree Bresser 2” eyepiece that wasn’t even mentioned in the ad!

Included in the purchase price is a 2” dielectric diagonal, finder scope and two speed focuser. After using “The Beast” for a while it became obvious that it needed a $200 dollar focuser upgrade just to make it usable for CCD imaging. Visual focusing was pretty rough as well. So when you add the $100 eyepiece, the $100 dollar 2” diagonal and a $200 dollar, 2 speed focuser with the AR 102, the telescope ended up being free! Over all the fit and finish is outstanding. Light weight, but well built. The focuser is very smooth and sensitive. This is important in short focal length telescopes since focusing is much harder to get right with the shorter focal length. The rings and dovetail are very sturdy and supply a handle to carry the scope with. The interior of the rings are covered with felt to keep the tube from being scratched. Clamps help to make sure the scope is oriented the way you want it.
The scope comes packaged in a double box with plenty of internal support. It arrived in good condition and quite fast. I also purchased a 5x Barlow lens and it was packed in a box and placed with the other accessories. Assembly primarily was taking off the rings and stripping off the protective foam, then putting it back together. At 11 pounds it is easy to transport and as was mentioned earlier, the built in handle really helps to make it an easy

I mounted the optical tube assembly on my old Celestron GT mount. This set up has flimsy tripod legs and lots of backlash but it is light and easy to use. With a 4,000 object database it will take you to most of the brighter optics a 4” scope can see. It also has a Baader dovetail clamp attached. This means anything with a vixen style dovetail can be mounted on it. Even with all the issues, it does track well and puts most objects near the field of view. Sometimes you have to use the finder but it is usually right on the edge of view in the eyepiece.

Now what about the optics? All of these fine features are of no avail if the optics are substandard. It has been a difficult task to test the optics this winter due to the bad weather. We live between two 10,000’ plus mountain ranges so the conditions are usually less than optimal, but this year has really been bad for astronomy. With a quick look at the ¾ moon in twilight (clouded up at dark!) I was impressed. There was a bit of purple fringing around the limb of the moon but not really any worse than “The Beast.” I used the 25mm, 70 degree, 2” eyepiece first just to check it out. This only gives you 26x but man what a field of view! The view was crisp and the face of the moon was very contrasty and showed rich detail. As expected, focusing was a bit more demanding but the 2 speed focuser made that chore much easier. The next time I got out the scope, I looked at Capella and did some basic star tests. At high power (165x) the diffraction rings looked good on both sides of focus. This test was a bit tricky since the conditions were so bad. There were high clouds and even stars overhead were twinkling. So the next time it was out, there were high cirrus clouds but a much steadier atmosphere. The moon was full so any CA would really show up. Using a 8.8 mm Meade 82 degree eyepiece and the Celestron Minus V filter there was only a hint of CA around the moon. When I switched to the 25mm, 2” eyepiece there was some purple fringing around the edge but I did not see it as being objectionable. It definitely did not affect the detail visible on the face. Before the sky was completely covered with a layer of thicker clouds I slewed to M 42 in Orion. Wow, even through clouds I could see the Trapezium clearly with the 8.8 mm and the 25 mm. It was much harder to differentiate the 4 stars at 26x with (25 mm) power but very easy at 75 (8.8 mm) and even easier at 188x (used at 2.5x Barlow with the 8.8 mm). When you add magnification, the views look very much like views with the 6” F/8, just a bit dimmer. So even with the short focal length, the scope takes magnification well and focusing is quite easy due to the 2 speed focuser. This was a concern with me since I did want to look at the planets from time to time. This scope is not maximized for planetary observing but still does it well.
The weak link to this set up is the Celestron GT mount, not the AR 102! Even with foam in the tripod legs, tightened up bolts, wooden blocks to force the legs out and bungie cords around the bottom of the tripod to help with vibrations it still jiggles a lot. Oh don’t forget the 11 pounds weight on the tripod tray. Even with all this it still has about a 5 second settle time and shakes with any breeze or touch. This scope on the Sirius mount would be amazing but again not very “grab and go.” As a short term fix I drilled and tapped the mounting plate on the bottom of the Nextstar GT so it would fit on the Sirius tripod. This fixed most of the vibration problems and made it a much steadier mount. The Sirius tripod has one and one half inch tubular legs. This provides a much sturdier foundation for this telescope.

My overall impression is outstanding! It is a great deal for the money, even at the non-sale price of $399. At the current sale price of $299 it is almost a steal! The optics are very good, the fit and finish are outstanding and it is light and portable. Overall, it is a real bargain. My only complaint is very minor. All the screws and fittings on this scope are metal except for 6 screws on the finder scope. Four out of the six screws on the finder rings are plastic and the two screws that hold the finder assembly on the optical tube are also plastic. It would seem to me that the dollar or so that is saved on the price of the screws isn’t worth it when compared to the total price and quality. However, they do work and hold the finder quite steady regardless of the nature of the screws, so I guess it is not really all that important. You could always replace them yourself if it bothers you that much.

Overall, I would highly recommend this scope as a low cost alternative to a more expensive ED or APO scope. Regardless of the quality, it will not give you the performance of one of these more expensive scopes. However, if you can live with a bit of purple in an image this is an outstanding scope!

Telescope Series Explore AR Air-Spaced Doublet
Telescope Optical Design Refractor
Refractor Design Achromat
Number of Refractor Elements 2
Telescope Aperture 4"
Telescope Focal Ratio f/6.5
Telescope Focal Length (mm) 663
Optical Coatings Explore EMD
Limiting Stellar Magnitude 12.5
Diagonal Included? Yes - 2" Star Diagonal
Telescope Eyepiece(s) Included? No, Sold Separately
Finder Included? Yes - 8 x 50 Finder Included
Focuser Style Crayford/Crayford Style
Focuser Size 2"
Focuser Speed Dual Speed