The Antares 152mm f/6.5 Refractor: Two Reviews

Exerpted from the Telescope Junkies Forum

Daniel Maloney:

First Light

Last night I got to try out the Antares 152mm Refractor for the first time. The night prior I had taken the Orion Argonaut 6'' Mak-Newt out for its first light, so I was just as excited to see what this 6'' could do! This refractor is shorter than most other 6'' refractors with a fast design meant to capture a wide field of view (f/6.5). It employs the standard rack and pinion focuser, although the one on this scope is well built (much better than the one on my AR-6) and also comes with a very well-built finderscope. The dew shield is very large as well, giving extra protection against dew.

I mounted this scope on my extra LXD75 mount. To give you an idea of its weight, it took two 10 lb. counterweights to balance it with a 2'' Willams Optics diagonal and an 8mm Orion Stratus eyepiece attached. I set the telescope type, re-calibrated the motors, did a quick two-star alignment and away I went.

Viewing

First object up was the Ring Nebula (M57). I put my 17mm Stratus in and took a look. It was very well resolved and the stars around it were pin-points, but there was some coma getting in on the edges of the field and much closer to the center than I would have thought. I totally expected some coma near the edges, being that it is an f/6.5; but this coma was farther in than I would expect at f/6.5 (read why below). The contrast was good (but not as good as the Orion Argonaut the night before) which could be attributed to the moon being higher in the sky than the previous night. I decided to stay with M57 and see what my 13mm Stratus would show me, just to see how the scope performed going toward higher mag.

Ouch! No matter how much I focused I could not get the stars near the center to come to focus. They exhibited the famous comet trails common with coma. I was scratching my head at this point. Why does the 17mm look so good but the 13mm goes into a coma-induced mania? I decided to star test Polaris to figure this mystery out.

Allow time to achieve equalibrium

I got the North Star into the center of the field of view with my Orion reticle eyepiece and started to star test with the 17mm installed. Immediately I noticed what looked like tube currents as the circular rings suddenly became elongated and then would become circular again, so I let it sit for another hour (at this point I had already had it outside for 1 1/2 hours). After another hour for equilibrium time, I was back at star testing and no more tube currents, hooray! Note to self: when the temperature difference is 20 degrees, give this scope at least 2 1/2 hours to reach equilibrium or an hour and 15 minutes for every 10 degrees. With the 17mm eyepiece, the diffraction pattern was very concentric both in and out of focus. So I put the 13mm in and what I saw astonished me. Just another 4mm was enough to show I had a collimation problem! I had pretty bad coma with the center pushing to the right. So I decided to cut the session here.

This is the first time I will have to collimate a refractor, so I got an Antares Cheshire eyepiece, designed to easily collimate refractors. (I wonder why they came out with it? ) It should be here next week so I plan to get this baby ready for a much better second light next weekend. I hope the results will be better next weekend.

Oh well. One great night (with the Orion Argonaut) out of two is not bad at all. I will keep you all posted on how the second light went next weekend.

Second Light

Well, I got the chance this week to correct the issues I had encountered with the first light for the Antares 152mm which were found to be a loose objective lens [shown right] (rattling) and collimation being off by a little bit. The issue I was running into last week in regards to coma was probably due to the collimation being off. What really surprised me was how loose the objective was. I had to turn the lock ring a lot to get the objective to stop rattling, and the lock ring was actually out of the cell quite a bit before I tightened it. In most cases the lock ring should be level or a little below the cell's edge. With that resolved and a touch up on collimation with the Cheshire eyepiece, I am happy to say that things were different this time.

On Friday night I attended our local star party at the Mansfield Dam here in Austin, TX, with the Antares in tow. After a quick alignment, I decided to just stay on the second alignment star (Deneb) a little bit just to see how the star diffraction pattern looked with the 13mm in and out of focus. The Antares did not disappoint me this time, the diffraction was textbook and I saw the airy disc we have all come to know and love. There was a little chromatic aberration (CA), but only about the same as the amount that my Meade AR-6 which has a longer focal length. I was not expecting apo performance. But wait, maybe not (read on below). I was stoked even though the loose objective had me really worried because other problems can arise from it rattling around (objective and inner lens not being lined up anymore, objective not centered, etc.).

Finding Objects

Ok, so star test was good. Now it was time for some objects! I first wanted to see what M8 (Lagoon Nebula) looked like with the 13mm Stratus eyepiece, and I was impressed. I do not remember seeing as much detail on the nebula with my AR-6 as I did with the Antares. I threw on the Orion Ultrablock filter and the 'wow' factor increased exponentially. Then I went after the Swan (i.e. too many names Nebula) M17 and again the nebula was very detailed without the Ultrablock, but moreso with the Ultrablock attached. With M22 I was again impressed with how well resolved the stars were. The core was very easy to discern and there was no evidence of coma besides the very edge of the field, which is what I expect from an f/6.5 and a wide field eyepiece in use.

I decided to give Jupiter a shot before it went over my parked car and out of view. At this point though, it was very low on the horizon so I did not expect to see much detail at high mag and I decided to try my 21mm Stratus (first without a violet reduction filter just to see how much chromatic aberration there was). I was impressed again not only with the level of detail, but also with how well the moons were resolved and how minimal the chromatic aberration was. The CA was still there but there was not a lot, meaning it was not thick on the edges. I just had to try my new Williams Optics VR filter so I attached it and I am happy to say that it worked like a champ. Every hint of bluish-violet color was gone. I did have to try the 17mm on Jupiter, but since it was so low in the sky it was like looking at it through water, and thus I stopped right there.

Summary

I viewed many more objects such as Andromeda (M31), M53, M3, M16, M18, M19, and M21 and they all looked better than I ever expected with this scope. Of course, everyone has high expectations of their new scope. I already own a 6'' AR-6 refractor and was not expecting the Antares 152mm to beat it, however, I would have to say it DID on only its second night out! Whether it is the faster design that yields wider fields, the semi-apo's ED glass, or a tad better collimation, I am not sure; but I just enjoyed the views the Antares gave over the AR-6. Even my buddy Jeff Phillips gave it the thumbs up which made me feel even better about it. The best part of the night, though, was when some kiddos got to take views of M8, M17, and M22 through it and hearing their 'ooohs' and 'aahhs' gave the final seal of approval.

I am very surprised by the performance of the Antares as it exceeded every expectation I had for it, especially after the rough start. She is definitely a keeper.

Daniel Maloney is the developer, technical advisor and frequent contributor to Telescope Junkies, the Andy's ShotGlass Amateur astronomer's forum.

Andy Raiford:

The scope was everything Daniel said it was! I found the scope to be quite surprising. The sheer size of the objective lens is something to behold, and yet, being an f/6.5 telescope, the overall size wasn't overwhelming. We decided to take it through its paces the other night even though there was a fairly stiff wind and the seeing was less than nominal.

The one thing I wanted to find out was: What on earth is "semi-ED glass" and does that equal a "semi-apo"? The term "semi-apo" is thrown around in astronomy circles as easily as "LOW, LOW PRICES" is thrown around on used car lots. One must take such terms with a grain of salt. The proof is always in the pudding.

So....was there chromatic aberration (CA) in the Antares 152mm? Yes. When you turn the Antares 152mm scope to view such bright objects as the star Vega, there is CA in abundance. Come on folks, it's an f/6.5 achromat! Was the CA as bad as other short focal length achromats? No. It seemed to be only about half as much, which must be where they get the "semi"? Who knows? I'd drop the "semi-apo" claim if I were Antares. This is a great achromat.

On everything else that we observed, (besides Vega) the scope performed beautifully. On a couple of objects, I was very pleasantly surprised. For instance, I have always enjoyed splitting the double-double - two sets of double stars near Vega in the same view, but only using 5" refractors. It's amazing how much the extra inch of aperture on the Antares 152mm improves that view. I was amazed. For the first time I felt like I was looking at two sets of car headlights floating in space. In smaller scopes I can certainly can split the stars, but in this one I was able to see a definite black space between each set. Perhaps what aided this was the baffle system that the Antares utilizes inside the tube. The contrast was very good, even from my light-polluted back yard.

Speaking of light pollution, we used the Orion Ultrablock filter on a number of objects such as the Lagoon and Swan nebulas. I was very surprised at our view of the Swan. It was the best view of the Swan that I've seen through a non-APO scope. There is NO way on earth one could compare this inexpensive doublet achromat to an $8000 triplet apochromatic telescope, and I wouldnt dream of trying. Believe me...I've looked through $8000 6" apochromatic telescopes. But if all you have in your wallet is $800 and you purchase one of these big honkin' refractors, the last thing on your mind during your first night under stars with this scope will be the fact that you don't have $8000. You'll be plenty happy with this one for a while.

Edited by Teri Raiford