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Celestron’s NexStar 11 GPS

Posted by Dannon Vick   07/15/2004 07:00AM

Celestron’s NexStar 11 GPS
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When I was ready to graduate from my beginner’s scope (a used, but loved Celestron 8i), I began to explore options. I quickly realized however, that driving a Volkswagen and having a love for astronomy could present some problems. I liked the computerized Schmidt-Cassegrain (SCT) design but there were so many options…9.25”, 10”, 11”, 12”, and even 14-16”. Knowing that I wanted as many inches aperture that would still fit in my back seat, Celestron’s NexStar 11 GPS (N11) was the chosen scope.

Ergonomics:

The first thing that attracted me to the N11 was the layout. With good handle placement and its tapered fork design, I knew moving site-to-site would be easy, and I wasn’t disappointed. The OTA and fork is well balanced and feels very similar to carrying a 65-pound child, with one hand lifting and one hand stabilizing.

The tripod breaks down into a manageable size for handling and storage, and all other components are small and easily handled.

Set up:

Attaching the OTA/Fork to the tripod can be somewhat hair-raising experience, especially if you are flying solo. To attach, first you must line up and set down the OTA/Fork drive base on a single centering pin, then rotate the drive base until it is lined up with three bolt-holes under the tripod head (which you are unable to see) and finally, blindly hand-screw the three bolts in. This procedure becomes marginally easier (albeit a strain on your marriage) if your spouse or other loved one assists you.

This is the single greatest design flaw that I can identify with the N11, but fortunately this flaw can be corrected with the addition of a $50 accessory know as a landing pad. This device auto-centers the OTA/Fork onto the centering pin and drop-locks the complex together for hands-free bolt insertion. It’s the difference between climbing a rope and climbing a flight of stairs. The landing pad should be the first accessory purchased for a N11.

Stability:

One of the biggest surprises of the N11 is how stable the entire system is. The tripod is reinforced with a center-leg brace and the dual-fork design makes for a very solid feel. Focusing the N11 will not lead to jiggles or wobbles, and when used with the supplied vibration-suppression pads, the N11 can be comfortably used in even a stout wind at high magnifications, and a bump from a careless bystander is usually dampened within a second or two.



Alignment:

The N11 is able to find north and download GPS data (location within 30 feet, and time within one second) usually within two minutes. Once you confirm the data, the scope begins slewing to a standard two-star alignment. The supplied 9x50 finderscope leaves something to be desired (although it’s quite an improvement over the “red dot” finder included with lesser models) and I recommend a Telrad or other “zero power” finder. This notwithstanding, the N11 is usually able to put the alignment stars within two degrees, and I’ve found that it is not uncommon for Vega to be in the field of view of a 35mm Panoptic (80 power) right off the bat! A through and highly accurate alignment can almost always be achieved within five minutes of power on.

Goto accuracy and Tracking:

Once properly aligned, I’ve found that the N11 can place any selected object in the field of view of a 22mm Nagler (~125 power) 98% of the time, usually in the dead center. The need for realignments is rare, usually only once every four to five hours.

Equally impressive is the N11’s tracking ability. At a recent star party, I inadvertently left my N11 on the Whirlpool Galaxy (M51) for over three hours. When I returned, I was pleased to find Whirlpool still in the dead center of the eyepiece. The goto accuracy and tracking of the N11 is very accurate and is a definite high point.

Collimation:

While the stock Allen-style collimation screws are somewhat of a pain, requiring a special wrench to make adjustments, there are several after-market thumbscrew sets on the market for about $20 dollars that make collimation a breeze. I travel with the N11 quite a bit (read that as “it lives in by back seat”) and I’ve only needed to collimate once every several months, but when I do, I can have it done in two minutes flat. If your worried about owning a scope that needs collimation, don’t…it’s almost a non-issue.

In-Field Performance:

Cooldown time on the N11 is surprisingly short due the

carbon-fiber tube construction. Celestron advertises cooldown times of up to 75% faster than an aluminum tube model. While I haven’t been able to achieve those results, I am frequently thermally stable 10-15 minutes sooner than a friend’s 12” Dob, and the times were on par with my old Celestron 8i.

The tripod can be set to nearly any height, making for a comfortable viewing setup for almost any observer. The seams and joints between moving parts are very tight and fairly resistant to dew and dirt. It should be noted that dew is a major issue, especially during the summer, requiring the constant use of a dew shield and a dew strip / zapper.

The focuser exhibits zero-image shift and requires usually less than one full turn, even when switching eyepieces. The focuser placement is a comfortable distance from the diagonal and makes for a natural feel, and as previously mentioned, focusing will not cause stability issues. Accordingly, a motorized focuser is not recommended.

The N11 is very quiet while full-speed slewing to objects, something like a soft hum (any quieter and you’d worry if it was working or not) and is completely silent while slewing at one degree per second or slower, as well as when tracking.

Optics: Solar System observing

The SCT design is frequently criticized for poor planetary contrast, but every N11 I’ve looked through has given sharp, refractor-like views. You’ll find (on good nights) that Jupiter will exhibit many cloud bands, with multi-colored whirls and festoons at even fairly low-powers. Saturn will exhibit at least a few cloud bands, satellites, and the Cassini division every time. On better nights you can see many fine bands of color and the Ekene Division. Mars shows a good deal of structure with the polar caps plainly visible with dark and light areas being a little tougher.

Venus and Mercury are pretty much featureless crescents (no scope can really help that) and Uranus and Neptune are surprisingly bright, albeit small, blue-green disks.

When viewing the Moon, especially at low powers, the 11” of aperture will instantly turn the unfiltered Moon into a freaking laser-beam, instantly obliterating any night vision that you might have acquired. Filtered views are crisp and, at higher powers, many craterlets are visible over the entire surface that are not apparent in smaller aperture scopes.

Optics: Deep Space Objects (DSO’s)

If the N11 gives good views of objects in the Solar System, it excels in DSO views. With a light grasp of nearly double an 8” model, many more open and globular clusters exhibit fully or mostly resolved star fields, and galaxies finally begin to show a good deal of structure such as dust lanes, bright cores and spiral bands.

A great deal more nebulosity is revealed in planetaries and reflection type nebulas, with fine details and vastly improved structure.

Stars are crisp pinpoints and there is good color differentiation and separations for most well-know doubles. For example the N11 can fairly easily split all four stars of Epsilon Lyrae…a.k.a. “The Double Double”, in the same field of view.

Recommended Accessories:

There are several “must have” accessories for the N11, and I would be remiss if I didn’t discuss them.
- Landing Pad: Guides, centers and locks the OTA / fork to the tripod for easy mating. By far the best accessory for the N11.
- Portable battery: I recommend the Celestron Power Tank, with two cigarette lighter outlets, several power jacks and a couple of really bright flashlights, it can run the system for several hours and will give you a lot of bang for your buck.
- Zero power finder: Telrad is my personal choice, and can be easily mounted to the ample OTA surface area.
- 2” Diagonal and 2” eyepieces: Why buy a Super Big Gulp and drink it through a coffee stir?
- Rigid dew shield and dew strips: Dew is your enemy, plus, if properly flocked, the dew shield will help improve image contrast.


Conclusions:

The N11 is a good balance between portability and large aperture. It gives excellent views of a very wide range of objects, and you can accessorize it like a G.I. Joe action figure. The flexibility of the system will rarely leave you wishing that it could do more, and you can’t beat the “wow” factor when people see it for the first time.

In the end is the N11 right for you? I suspect that if you are reading this review (and made it this far) you have at least considered purchasing the N11. Let me pose a few questions to help you decide:

- Are you willing to pay up to three times the amount of money for a SCT goto design over a Dobsonian “push-to” design of similar aperture?
- Do you travel to different observing sites often?
- Do size constrains prohibit you from the use of a medium-aperture reflector / refractor or larger aperture SCT?
- Do you enjoy a wide-variety of after-market accessories?
- Is the flexibility (imaging, tracking, goto, etc.) of the N11 more important to you than the simplicity of a reflector / refractor?
- Do you currently have 9.25” or less and are suffering from “aperture fever”?

If you said yes to the first question and yes to at least three of the five remaining questions then you will be elated to own the N11.




Click here for more about the NexStar 11. -Ed.