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Celestron Nextar 5 Schmidt Cassegrain

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Date: 7-20-2003
Price: approx $1000.00 to $1500.00 depending on options
Design: Small and mobile GOTO Schmidt Cassegrain.
Description: 5-inch Schmidt Cassegrain on an Alt-Az GOTO mount with a small reflex finder scope.

The Reviewer

I have been observing since I was 6, and now that I am 29 I have acquired the financial autonomy to buy an eyepiece now and then. I would not rate myself as an expert observer as I have been in and out of the hobby, and as most amateurs, especially those who are married, have children and live in urban areas, have too little quality observing time. I have two places to observe: my garden in Northern France with 120 clear nights a year and Mag 3.5 skies, where I just give a little glimpse when it's clear at the moon and planets (the Orion nebula is "seeable" but a sure disappointment) , and a place in rural, southern France with darker and clearer skies. There I hunt galaxies and globulars which are my favorite targets, but I only have a handful of good nights there per year. My e-mail is mathieuchauveau@hotmail.com.

I have at my disposal for a couple weeks a Nexstar 5, which was second hand, and could not resist the temptation to write you guys about it. I have been a low-tech astronomer all the way (the highest tech scope I had ever used was a RA-driven '79 Celestron 8, all others have been undriven) , so I wanted to see if GOTO scopes were such a great thing. Also, as the scope is a couple years old, this review also serves to report how these telescopes "age".

I tested the scope with my usual Plossl and Lanthanum Eyepieces (lately I sold a lot of my "budget" eyepieces, reducing my collection to single figures!), and also with two Ultima eyepieces I received with the scope. But the goal of the test was more in the mechanics than the optics.


Outside View

The scope was delivered to me in a JMI case (on which I won't report because I only used it for travel once). It came with the cigarette-lighter-type plug cable.

Optics

The first surprise was the Schmidt corrector did not stand firmly in place. It had a little lateral wobble. This did not prove a problem while observing, I would star-test the corrector into place (moving it until the shadow of the secondary was aligned with the out-of-focus star disk). Not very elegant but totally effective. Finally I realized the corrector was retained into place by a two-hole ring like the retaining ring inside
eyepieces, so I used a compass point to screw the ring tight (I somehow managed not to scratch the corrector plate in the process).

Using the scope shows contrast is good, and that is obviously thanks to some
serious baffling. However one will notice the inside 'Cassegrain' baffle is very narrow, meaning you cannot use a "long-tube" Barlow lens. My short-tube Barlow fitted well however.


Mount

The tripod looks cheap, but for visual use is fine. It is the standard-issue Chinese tripod, the same as on the EQ3-2. I am happily surprised at how well it holds it.

Focus Knob

PRO:
it is very smooth, and as a result the view does not wobble when you adjust focus (I had an AZ mount before, by the time the vibrations had dampened out, Jupiter had vanished out of view).

CON:
There is one complaint, which is mechanical but has an effect on the seeing: the knob has a "tick" feeling to it, and sometimes at high power you have the feeling that you are half a tick inside or half a tick outside of focus. On the Moon and Mars, I could achieve focus at high power, but had to be careful to turn the knob by less than a full tick.

Visual Back / Diagonal

The 1 1/4" visual back has two tightening screws, and it is a good thing as the diagonal wobbles noticeably in its barrel. It is mildly irritating and you have a little fear that heavier eyepieces might fall off (they do not, but you have to be careful to tighten those screws hard). I did not have extra diagonals at hand so I cannot say if the outside diameter of the diagonal barrel is too small, or if the inside diameter of the visual back is too wide. Price issues are obviously at work here.

Finderscope

The N5 comes with a Starpointer finder (which I reviewed elsewhere), which you use only for alignment purposes. Nothing wrong about this thing, to the contrary.

Using the Scope

GOTO

The scope came without a manual but it was OK. The only thing which took me a while to get is that the arrows you must use in the menu are not the same arrows you use to point the telescope. So for about an hour every time I tried to change alignment stars, methods, etc, the OTA would slew up and down!

The first thing you do with this scope is align it. There are two procedures : "auto align" and "2 star align". I think the auto-align is for absolute beginners who know nothing about astronomy, but are experts in time zones and geography. You have to put
latitude, longitude, determine the north, local time, what time zone you are in, if you are in Daylight or Standard time... blahblah. Even if you can automate some parameters, it's a drag. I think the 2 star alignment is much easier: you choose in a list a star (let's say Vega: the stars are ordered by name), slew the scope to Vega with
the hand paddle, press "align", then pick another star, like "Arcturus", slew there and press "align", and voilą! The longest part of the alignment procedure is the slewing between the two alignment stars, so at most it's a two minute operation.

After a handful of objects, the alignment tends to slip out, so you can readjust. Let's say you are looking at M27, you notice that the scope puts M27 on the edge or even outside the field of view. You center M27 and press "Align" to instruct the Nexstar to use M27 as a new reference point, and everything should be better. I suspect that after a couple years, something in the gear department must wear down, and the tracking is not that good anymore (you are instructed not to move the scope by hand, but someone IS going to move that tube at some time and it may damage the gears). If some of the good people at Celestron want to react to this they are welcome.

However the alignment, or its influence on GOTOing, is not super-sharp. You need to put a low-power eyepiece if you want to be sure the object is in the field. That might become a problem if you hunt faint galaxies or small planetary nebulae. However with a 5-inch scope, you are not going to knock down an NGC Marathon anytime soon. It looks like the instruction in the alignment procedure that asks to point the tube roughly at horizontal is quite critical. Maybe you should invest in one of those stackable bubble
levels.

The GOTO has a distinct advantage from urban locations: you don't need to know the stars, and it's a good thing as you can't see them. I saw M13 and M92 without being able to see the
Hercules Square . I discovered objects I had never or seldom seen, that are bright and interesting but which I had never seen because they are out of easy star-hopping patterns, the best example being M3.

The GOTO has the full Messier,
Caldwell , NGC Catalog, plenty of stars and double-stars. The double star catalog uses common names (Mizar, 95 Her, etc...) but the star catalog uses "proprietary" numbers. I did not bother using it, nor did I use the GOTO to look for planets (it will ask you date, time, etc...).

Slewing

Slewing: there are many slewing rates (9), but I think fewer would have sufficed. For example you can't tell the difference between speeds 4 and 5. On the slower rates, there is an awkward feeling: when you press the button, you hear the motors for a couple seconds, then the slewing begins. I was told by the previous owner (who, by the way, answered promptly to my myriad questions) that it is a backlash effect and that there is a menu in the Autostar to adjust this. I wonder why this is not factory-programmed. The good point is that it does not seem to affect the alignment much.

On slewing itself, there is something I hate about these paddle-operated scopes: you never know which way it is going to move. I operate a 16" Dobsonian and trust me, when you slew it, you feel it, and you know which direction you are going. Here you don't have the physical feedback helping you; and when the scope slews fast, it goes too fast for you to see which way the stars are moving (especially faint ones). It's probably a personal feeling.


Tracking

Finally, there is the tracking once you have locked onto an object. It is nothing to write home about, but is fine for visual use. You can center (I should write centre as I am Canadian) an object at 100x, get inside to check your atlas or put the laundry in the dryer, get back 10 minutes later and the object is still there. So you do not have much more to ask from this function. On high-power planetary work, however, you will need to adjust now and then.

Mount Performance

The single tine mount is perfect, especially with the hand paddle fitting in the arm. For visual work, even at high power. There is nothing wrong with the tripod, either with legs up for stand-up use or down for sit-down observing.

Optical Performance

Deep Sky

From my suburban home, M13 was resolved. M3, kind of. The Ring nebula is a nebula shaped like a ring. The Dumbell nebula is shaped like a dumbell. However the Owl Nebula is not visible from here. I have observed the same objects with my now-departed Tak Sky 90 and the Nexstar 5 is better on deep sky, both for resolution and light gain. I have read elsewhere that a TV85, or some other high end refractor in that aperture range, would outclass a C5, but I think here the N5 is slightly better than those refractors, at least on deep-sky objects.

Planets

The only planet I have had the opportunity to see is Mars, at about 18" on the eve of its historical opposition. Very good. In the dawn sky, the planet being only 30° above the horizon and 10° above the nearby apartment buildings, I could see the features that the ALPO website afterwards said I should see (to avoid the "Schiapparelli effect" and convince myself I was seeing features that were not there, I made a sketch of what I saw, and then compared it to the simulated wave on the website). I had guessed there were three dark features in the south tropical region, and they were actually . And I had not looked at Mars in years, so did not "remember" what was to be seen.

This was done at fairly high power for such a scope. A 4mm Plossl giving 312x was the max, the atmosphere obviously the limiting factor but the view still pleasing. Mars was gibbous and even at that power I could tell the sunlit rim was sharp and the terminator was softer. A Barlowed 12mm Radian showed that there was no detail to be gained past 200x, but at 312x the view still held.

The moon was OK for a 5-inch telescope; typically the atmosphere is the limiting factor, not the optics.


Double Stars

And, finally, I must admit that this scope has given me a liking for double stars. I used to think double-star observing was so 30 years ago, with people spending their money on 3" refractors and then comparing them with 2.4"s. Well, I still think that way, because splitting the double-double gives me nothing like an M13 rush, and I'd rather test my telescope and observing skills on a 13th Mag. galaxy. But it also look we are in the golden age of the 4" Apo, and thanks to the GOTO I have taken the habit to check out doubles while the sky gets dark and the scope cools down (I hear the veins of double-star observers everywhere popping, and those guys jumping off their chairs, yelling: 'what! This guy is insulting us! And then he insults double stars themselves by looking at them during twilight, with, of all things, a thermally-unequilibrated SCT!')

Blah blah blah, so both colorful double stars such as Albireo are a treat, and close ones like Epsilon Lyrae work well. On Epsilon you see that this is a small scope, with a rather large Airy disk, so the Airy disks of the pairs are merged together, but the stars themselves are clearly separated. I am not experimented in the seeing double department so I will not elaborate. I think seeing doubles was easier with the Tak 90, where there was less light dispersed in the airy disks. I think.


Conclusions

- The GOTO module is a godsend but not a miracle: you will save plenty of time and see many more objects than before, but you will still have to do a little panning now and then to find stuff.

- Optically, this is a surprisingly good 5" telescope, considering it is Airline-overhead-bin compatible and sells for around $1000 (looks like if you wait your time you can have the GOTO paddle and tripod free at that price).

- At that price, the prism diagonal with a 1.2489" barrel is a no-show against your $250 luxo-diagonal, but you can suggest an upgrade to a decent diagonal as a great Christmas gift.

- watch out to that narrow baffle if you want to get a Barlow or any other OTA-intruding equipment with it.

- Great scope for deep-pocketed, small-car beginners, with enough aperture to do a little deep-sky work.

- Great SECOND scope for experienced observers who want a travel scope or a quick-out scope. I do not think one would want to step down in aperture for portability's and GOTO's sake. It was nice to have it around but if I only had $1000 to spend on a scope I would take something else.

Submitted by Mathiew Chauveau - mathieuchauveau@hotmail.com - France

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