iOptron's new 6-inch Mak & German Equatorial Mount: these recent additions to the iOptron family of telescopes and mounts are aimed at serious observers and astrophotographers.
SINCE LANDING ON the astronomical scene in late 2007, iOptron has continually introduced products aimed at an ever-more sophisticated audience. And two of the latest--a 150-mm (6-inch) Maksutov-Cassegrain telescope and a mid-weight German equatorial mount--are clearly designed for serious observers and astrophotographers. As our bitter New England winter begrudgingly gave way to spring earlier this year, I spent several weeks testing both products, which were on loan for this review.
My colleague and long-time Mak enthusiast Gary Seronik has reminded me more than once that 6-inch Maks strike a balance between aperture and thermal performance, since larger-aperture Maks often require impractically long times to acclimate to changing ambient temperatures. All of my testing was done with the iOptron MAK 150mm housed in my backyard observatory and when temperatures remained relatively stable. As such, thermal issues were not a problem, and the very subtle heat plume I could sometimes detect rising from the light baffle during early evening in out-of-focus star images did not affect in-focus views.
The scope is a Rumak design, meaning that the secondary mirror is a separate optical element glued to the inside of the strongly curved Maksutov corrector, rather than being a spot aluminized directly on the corrector's surface. This gives optical designers an additional degree of freedom, which can be used to produce a scope with better color correction, a flatter field, and, most importantly, better off-axis star images. The iOptron MAK 150mm does indeed deliver excellent star images across the field.
Several years ago I tried a similar-looking 6-inch Maksutov marketed out of Asia that had equally good optics but was hobbled by a sloppy focusing system. That's not the case with the iOptron model. In addition to having a dual-speed focuser with a very light touch, the MAK 150mm's focuser has an internal preload that makes focusing very precise. The preload also makes images return to the same spot following the slight image shift that occurs when you reverse the focusing direction. This is a nice feature for anyone doing high-magnification recording with webcams and other imaging devices with small detectors.
As with all compound telescopes that focus by changing the separation between their primary and secondary mirrors, the MAK 150mm's effective focal length depends on the location of the focal point, and it increases as you move the focus to a point farther outside the tube. My typical configuration for visual observing included a 2-inch star diagonal (pictured on the facing page) and, with 1V4-inch eyepieces, an adapter that required the focus to be a bit farther out. At this location I measured the effective focal length as 2,095 mm, yielding about f/14, with a working aperture of 145 mm and a central obstruction of 57 mm. These values are all well within expected limits.
This scope excels for observing the Moon, planets, and brighter double stars. With Jupiter slipping into trees on my western skyline and Saturn hanging low in the southeast during the evening, I spent much of my time exploring the Moon and hunting down interesting double stars, with magnifications as high as 420x (using a 5-mm eyepiece) when the astronomical seeing would permit. I particularly enjoyed the views at 210x and 350x with the new 10- and 6-mm Tele Vue Delos eyepieces reviewed in last month's issue, page 58. That said, it's worth noting that the scope's long focal ratio is very forgiving of eyepiece design, and I also had very good views with much older Plossl and orthoscopic eyepieces, and even lowly Kellner eyepieces delivered pleasing views.
Overall, I'm very impressed with the quality and performance of the MAK 150mm. In normal use with the included 8x50 finder and metal dew shield, the scope weighs about 17 pounds (almost 8 kg). As such, users will want a solid mount, particularly if they plan to do a lot of high-magnification observing. I found the scope ideally matched to iOptron's new German equatorial mount, so read on.
iEQ45 German Equatorial Mount
The next time I need a reminder that I shouldn't judge a product based on early impressions, I'll just think back to my experiences with iOptron's new iEQ45 mount. I was very taken with the mount as I set it up and checked out its impressive set of features. That enthusiasm, however, was ratcheted back a few notches when I started testing it at night. But my initial impressions returned as my testing gave way to simply observing. Here's why.
The iEQ45 is well engineered and manufactured, and it has numerous subtle features that make it one of the most portable mounts in its class. For example, the counterweight shaft stores inside the declination housing, and since the whole equatorial head weighs only 25 pounds (11 kg), the mount is extremely easy to carry as one piece. It comes with interchangeable dovetail saddles that accept scopes with either Vixen or Losmandy-D dovetail plates. The main electronic module is permanently attached to the polar-axis housing, and it takes only seconds to connect the hand control and cable for the declination motor. The mount runs on 12 volts DC and it comes with a universal AC adapter as well as a power cord fitted with a standard "car" plug.
The mount has a bubble level, fine-adjustment controls for altitude and azimuth positioning, a latitude scale, a built-in polar scope, and a very nice polar-alignment routine. Here's how it works. Within a minute or so of powering up the mount, the electronics automatically acquire a GPS link and the hand control displays a graphic image of where you should position Polaris on the polar scope's illuminated reticle to achieve proper polar alignment. You then make the necessary adjustments using the mount's fine-motion controls for altitude and azimuth, and you're done. From start to finish the process can take as little as three to four minutes.
I checked the reticle's scale and its concentricity with the polar shaft's axis of rotation and found both to be spot on. Combined with the graphic display, it made the alignment process very accurate, as well as intuitive. This is a great system for people who set up the mount in the field and want precise Go To performance as well as accurate tracking for astrophotography.
At this point things couldn't have gone more smoothly, and I turned my attention to testing the mount's performance. The good news? The mount is remarkably stable for its weight; Go To accuracy is commendable, even when executing "meridian flips" and switching between observing in the eastern and western halves of the sky; and the drive's periodic error is only about 19 arcseconds before training the electronic periodic-error correction.
The bad news? I found several aspects of the hand controller somewhat annoying. Foremost is the need for slow and deliberate keypad entries. If you're accustom to rapidly entering data on a keypad (picture a teenager tapping out a text message on a phone), you'll need to slow down to use this mount. I found myself having to verify each entry by looking at the display. Adding to this is a menu structure that, while relatively intuitive, is lengthy, and you generally start from the beginning of the menu each time you want to enter a new object or command.
At first I found this frustrating, but in reality much of my annoyance arose from testing the mount rather than observing with it. As such, I was constantly making keypad entries and hopping from object to object. It was only when I settled into "observing" mode and spent more time looking in the eyepiece than fiddling with the keypad that my attitude changed.
When observing, the only time that the lagging keypad response was noteworthy was when I used the direction keys to move around the field of view, since the scope would continue to move for a fraction of a second after I stopped pressing a key. With high slew speeds, this would cause me to overshoot my target. The simple fix is to select another speed, which you do by pressing a single digit key.
I could nitpick other aspects of the mount's hand control, but this would unfairly detract from what I consider to be an excellent mount. After all, the things that are really important--fast and precise polar alignment, excellent stability, accurate tracking, great Go To performance--are all there with the iEQ45. And these features, especially the stability, made high-power observing with the MAK 150mm a very pleasant experience.
The iEQ45 is rated for telescopes weighing up to 45 pounds (20 kg). There's nothing magic about this value, it's simply the weight above which the manufacturer feels the mount's stability becomes compromised. I tested it with several telescopes, including a long-focus 4-inch refractor, and loads up to about 30 pounds (50 pounds with counterweights), all with excellent results. For many years my workhorse portable German equatorial mount has been a Vixen Great Polaris DX. The iEQ45 is equally portable, has twice the load capacity, adds Go To pointing, and outperforms the Vixen in every way, all for not much more than the cost-adjusted price I paid for the Vixen. In my mind that makes the iEQ45 an excellent value.
What we liked:
First-rate image quality
Precise dual-speed focusing
What we didn't like:
Beefy tube requires heavy-duty mount
What we liked:
Excellent stability & load capacity for its weight
Accurate polar-alignment system
Excellent Go To performance
What we didn't like:
Slow response during keypad entry
Limited astronomical data shown on hand control
It comes as no surprise to his friends that Sky & Telescope senior editor Dennis di Cicco can enter data on a telescope hand control far faster than he can compose a text message on his cell phone.
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|Title Annotation:||S&T Test Report|
|Author:||Di Cicco, Dennis|
|Publication:||Sky & Telescope|
|Article Type:||Product/service evaluation|
|Date:||Jul 1, 2011|
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