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Comprehensive review of Celestron NexStar 11 GPS XLT


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I was interested in astronomy for 8 years, but still had my old 6,5 cm Newtonian reflector for both planetary and deep sky observations. Finally I have decided to buy more serious instrument for both visual and photographic sessions. It was quite hard to decide what scope will fit my needs, so I have searched through various forums and reviews for the opinions about one or another product and finally I have chosen Celestron Nexstar 11 GPS XLT scope.

I have already checked my scope for any flaws in the USA, just few days before my flight, just to be sure that no surprises are waiting for me at home. The scope was very well packed in the double carton box with the thick foam inside. I have made the quick inspection for optics and electronics. As the first observation went smoothly so I packed my scope for a long trip home…

The following comprehensive review about the scope and accessories will be in the following order:

  1. Kit accessories
  2. OTA
    • OTA construction
    • Optical quality
    • Performance “in the field”
  3. Mechanics, electronics and software
    • Construction
    • Performance
    • Handpad software

Kit accessories

The Celestron Nexstar 11 GPS XLT scope came with the following accessories:

  1. Standard tripod with central plastic spreader and rubber pads.
  2. 40mm 1,25” E-Lux eyepiece
  3. 1,25” Visual back
  4. 1,25” Prism diagonal
  5. 9x50 Finderscope with quick release bracket system
  6. 110 Volt AC adapter
  7. Nexstar hand control unit
Standard tripod

It weights about 9 kilograms and is very portable indeed. It has a small central pin in it’s head for proper scope alignment upon the scope assembly, but believe me – it’s very hard to properly align the scope’s base with this pin in the dark for one person. As I have my scope for more that 3 years, I’m already get used to that alignment of scope and tripod in the dark, but Celestron should think for the way better solution in the future.

Some astronomical dealers offer the quick landing pad solution, and that’s the way you should go if you want the easy set up procedure of this beast every observing night !!!

The central tripod spreader is made of solid plastic which firmly holds the 3 tripod legs. I have heard several complaints about this spreader being too fragile when setting up the scope and I must agree that the spreader should be made of metal for all occasions (the new CPC series scopes have more sturdy tripod and central spreader).

There are three rubber pads mounted on the very end of the legs of tripod. They should dampen out the vibrations caused by gentle wind or very small bumps to the scope. Unfortunately, they add more instability instead of removing any small vibrations. I have checked the stability of tripod with and without those rubber pads in various surfaces… And I must say that the best results (the way better) were without those rubber pads for both grass and concrete.

The tripod is quite stable for visual observations (without those three rubber pads, of course), but the situation changes entirely when I am trying to use the scope on the wedge for photography. The tripod is too inadequate for 11” scope. It will hold 8” perfectly, but 11” scope sits quite steady only for visual observations.

The tripod has an ability to be lifted to the desired height (it looses the stability, so you should consider using that feature for special occasions only).

The scope can be firmly put on the top of tripod and secured by three locking bolts. It could be done without any wrenches, with bare hands. It is great solution for quick visual observation session set up. I have tried to check out what time does it usually take for me to set up the scope and it takes up to 10 minutes for one person, and 4-7 minutes for two persons to set up the NS 11 GPS XLT scope (with full alignment procedure).

For photography solution, the equatorial wedge should be used that should be firmly secured on the tripod (using other three holes) using bolts with special wrench only.

Pros:
  1. Tripod is very portable
  2. Scope can be easily secured with three bolts without any wrenches (for visual observations)
  3. Quite sturdy for holding the 11” scope for visual observations
  4. Tripod can be lifted to the desired height
Cons:
  1. Central pin is too small, and it is very hard to set up and align the scope to the tripod at night (especially for one person).
  2. Tripod spreader is made of plastic
  3. Three rubber pads at the very end of each tripod leg add more instability, instead of removing any small unwanted vibrations.
  4. Tripod is too inadequate for 11” in EQ-wedge mode
  5. Lifted tripod will lose it’s stability so this feature is useful in special occasiod visual observation sessions only.
Eyepieces

Celestron have included 40mm E-Lux, 1,25” type multi-coated eyepiece. It has comfortable eye relief, and works good on deep sky objects that are of larger angular diameter. Unfortunately it has multi-coated lens only, so you will not achieve maximum light transmission observing the dim objects. This is the only one eyepiece that comes with the scope, so if you are planning to observe planets, think about additional eyepieces, or their sets.

I have taken an opportunity to buy Celestron eyepiece kit for just 99$. There are 6 fully multi-coated Super Plossl eyepieces (4mm, 6mm, 9mm, 15mm, 32mm), 2x Barlow lens and 6 planetary filters with their instructions as well. This set of eyepieces will definitely fit all the magnifications scale you will need at first.

For wide angle (about 1 degree) observations, you should consider to buy additional f/6.3 focal reducer and use it with your 1,25” eyepieces, or buy true 2” visual back and use 2” wide angle eyepieces.

Pros:
  1. 40mm, 1,25” E-Lux eyepiece is good choice for wider angle deep sky observations (though f/6.3 focal reducer lens are really necessary for more wide field).
Cons:
  1. Multi-coated optics. Fully multi-coated optics would have a greater light transmission, that is essential when observing deep sky objects.
  2. Only one eyepiece comes with the scope. You should think about some eyepieces set to fill all the magnification scale needed for observing various objects.
The other complaint could be addressed to 110 Volt AC adapter. Thanks god that I have additionally bought 7Ah power tank witch has 110-220V compatible charger. Celestron should offer the dual voltage AC adapter for both USA and Europe users.

The quick release bracket system that came with the good quality 9x50 finder scope is a great solution for quick set up of the scope. Once you have aligned your finder scope – it will stay aligned for the future observing sessions.

The 1.25” prism diagonal has really excellent quality. I had the ability to test the reflectance of this prism, and can joyfully say that it exceeded my expectations. It’s results are about 97% of reflectance in red spectrum (so in green spectrum it will be a bit more). Really great stock prism.

The hand control unit could have been more comfortable when using gloves (it’s really hard to push the right position buttons with the gloves on). The LCD display starts to dim noticeably in lower than -5°C, so it is hard to use it under very cold conditions. The menus and hand control features are easily stated, so there shouldn’t be any problems for newcomer to understand how to use the telescope during the very first observing session. More information about Handpad software you will find at the “Handpad software” section later.

Optical Tube Assembly (OTA)

OTA construction
Carbon fiber OTA

Celestron NexStar 11 GPS XLT scope optical tube is made of aluminum and Carbon fiber. The front part of the tube, that holds the corrector plate and secondary mirror, is made of aluminum. The middle, longest part – Carbon fiber, and the back of the OTA is also made from aluminum alloy.

As Celestron advertised their new Carbon fiber optical tube material being less sensitive to temperature changes (that will require less refocusing during visual and photographic applications), I have decided to order the GPS unit with Carbon Fiber Optical tube as well.

After some observing sessions I made it clear that Carbon fiber material doesn’t make the influence to the lower tube expansion due to temperature changes because the front and the back of OTA were joined by the 2 aluminum holders (illustration 1). They are firmly secured with screws to the both (front and rear) ends of OTA and as they are of aluminum, they will definitely expand or contract notably more than CF material due to the temperature changes during the session. That makes me sense that Celestron offered the Carbon fiber tube without considering redesign solutions of the OTA itself. There is no real advantage of using CF OTA in this situation. Carbon fiber will have the benefit of lower expansion (as it really has) only if the telescope tube will be straight secured to the fork arms, but not like in this Celestron Nexstar 11 GPS construction.

The other disadvantage of CF tube material is a bad heat conduction and that means that reaching thermal equilibrium using CF OTA will be really challenging. I have made several tests as well as I have read other reviews about CF tube and can confirm that reaching thermal equilibrium with my scope in our region, where temperatures rise and fall quite rapidly during observation sessions, is almost impossible. It will take almost 3-5 hours for the scope tube to approximately reach thermal equilibrium (from +18°C to -10°C). The best solutions to avoid such time costs are:
  1. To leave the scope in the open air environment for several hours before session
  2. To leave the back of the tube (where you install the visual back) open so that the warm air can go out (but that will result of dust appearance inside of the tube and, especially, on the secondary mirror)
  3. Buy the optional cooling fan specially made for telescope cooling and put in inside the baffling tube before observing session.
  4. Make some tube enhancements and add the permanent cooling fan to the back of the scope (as Meade have offered this solution for their new RCX series scopes).

The warm air in the aluminum OTA’s will cool faster than in the CF tube thus making observation session more effective. In the following picture (illustration 2) you can see how the de-focused star looks in the scope being more than 3 hours outside. The temperature ranges were from +16°C to -3°C. As you can mention, the whole star picture is still “boiling” as well as the very top of the de-focused star has vertical aberration or lifting. It is nothing more than the warm air going out through the CF material. And that affect is still noticeable after 3-hour observing session !!!

The main CF tube advantage over Aluminum (in this cope construction) is scratch and bump resistance. In those cases where aluminum tube will bent or distort because of rough handling, CF tube will not suffer at all because CF material is much more resistant and durable.

Fastar system

The front of the tube has the aluminum ring that holds the corrector plate, the secondary mirror holder, and the secondary mirror itself. As this model of scope has Fastar compatible system, that means that you can take out the secondary mirror and use your scope as F/2 wide angle photographical lens. Everything is just fine except the thing that when you are trying to unscrew the secondary mirror holder ring, the whole secondary mirror holder (with the mirror itself) turns in the corrector plate also. In this case, you definitely loose any optical alignment between primary/secondary mirror surfaces and corrector plate. I have heard a lot of complains about this annoying issue from other amateur astronomers abroad, and as a rule of thumb I have got that problem too.

When you loose such optical alignment, the best solution to get everything in place is to send your scope back to your dealer or turn everything to the right direction by yourself. It can be made by taking out the secondary mirror and inspecting the secondary mirror's fixing notch. It should be looking to the 3 o’clock position of the corrector plate, so when you install the secondary mirror, it will be pointed to that position as well.

To make the alignment more precisely, you can take out the corrector plate retaining ring, and find the serial number of the corrector plate. That secondary mirror fixing notch (in the secondary mirror holder ring) should be pointed straight to the center of the corrector plate serial number (but it is practically always in the 3 o’ clock position).

In conclusion I must say that the Fastar system introduced by Celestron was the unique solution to use your scope more versatile, but unfortunately that system should be made more precisely in order to give you more advantage instead of some problems.

Collimation (aligning the optics)


The general optical alignment can be made by adjusting the secondary mirror position relatively to the primary. This can be achieved by turning 3 adjustment screws (illustration 4) to find the best alignment of the system. Schmidt-Casegrains keep collimation very well, so this scope has the same advantage as well. I need to make only 2 re-alignment sessions in 6 months (when using the scope visually). For faster and more easy alignment procedures I would recommend everyone to get the optional Bob’s knobs collimation screws.

The back of the Optical tube assembly also require some comments.

Focusing system

First of all it’s clear that you will be confronted with the focus shift problem. As Celestron has advertised their primary mirror focusing system being of higher grade, it’s clear that you will definitely suffer from some amount of mirror shift. I can add that Celestron should offer some mirror lock feature (as Meade Schmidt-Cassegrains have) to get rid of mirror shift issue and that would have been greater improvement than just making the primary mirror focusing mechanism of the higher grade. You will find more information about the mirror shift issue on my scope in the “Optical quality” review section.

Baffling system and stray light issues

The baffling tube of the 11” scope practically doesn’t cut any stray light. Those small groves (usually seen in the threaded parts of eyepieces) inside the baffling tube (where the primary mirror slides) cannot be considered as being baffles. The main reason for Schmidt-Cassegrains being not so sharp when viewing planets are not caused by their medium-higher (34%) central obstruction or the quality of optics (in mass production units) but are caused by the stray light and various reflections inside the tube coming from the bright objects. That can be eliminated by adding some advanced baffling rings to the tube walls, secondary mirror shade, and primary baffling tube. However, no baffling system (or almost no) could be found in the Celestron NexStar 11 GPS scope. I have darkened the tube walls with the Protostar flocking paper and can confirm a better contrast when viewing planets and Moon. You can see what is the difference between original tube and baffled one in the pictures above.

Primary baffle tube inner diameter is a bit more than 2”. That will give you the fully illuminated field of view (FOV) benefit when using 2” eyepieces and accessories. It’s a shame that Celestron adds the much smaller than 2” adapter ring for visual back adapter and/or for focal reducer (which can be used effectively with 1.25” eyepieces only). The opening diameter of the adapter ring is only worth for 1.25 prism diagonals, eyepieces and other accessories. You should buy the optional, 2” inner diameter adapter ring (that will be threaded to the 3” back of the Celestron scope) to effectively use wide angle 2” eyepieces and other accessories.

The summary of the optical tube assembly design and mechanics:


Pros:

  1. The Carbon fiber tube has the advantage versus aluminum of being more durable
  2. Optical system is Fastar compatible, so you can turn you telescope into the ultra fast, f/2 lenses
  3. The secondary mirror can be easily taken out for cleaning and maintenance
  4. The secondary mirror has the lineup mark for optical alignment
  5. The secondary mirror holder has the fixing notch that can help you to align your system to the original state
  6. Primary baffle tube inner diameter is approx 2” - good field illumination with 2” eyepieces
  7. Excellent fit and finish of the whole OTA
Cons:

  1. Closed optical system almost without any ventilation (longer cool-down time)
  2. Optical tube is secured by two aluminum OTA holders (from both sides), that causes tube expansion and contraction due temperature changes and practically eliminates CF advantage of being more stable material
  3. CF is a bad heat conductor (longer cool-down time)
  4. Secondary mirror holder is insufficiently glued or fastened to the corrector plate and that causes some problems when trying to take out the secondary mirror
  5. The inner OTA walls are not as black painted as it could be
  6. Almost no baffling system. You should make some flocking enhancements by yourself in order to improve the contrast and resolution by eliminating the stray light and some reflections when viewing bright objects.
  7. The stock 2” adapter ring opening diameter is only worth for 1.25 prism diagonals, eyepieces and other accessories.
  8. Focusing system use the primary mirror sliding mechanism causing mirror shift issue
  9. Focusing mechanism does not include primary mirror lock solution
  10. Additional, permanently integrated cooling fan could be a great solution for speeding up the cool-down time of the OTA.

OTA optical quality

Celestron’s optical quality has always been in the top among other manufacturers and this rule hasn’t been broken with my scope either. In fact, I am very pleased with my scope’s optical quality for both deep space, and planetary observations… The in-out focus star images were very very close to perfection: no astigmatism or other major aberrations, diffraction rings are almost identical in both sides of focus (when the scope has been cooled down, of course). I have checked the optics by various ways: using artificial and real stars, observing the planets and double stars using very high magnifications… and even using Ronchi tester.

Prior to test the optics with Ronchi tester (133 lines per inch) I made sure that Easytester’s Ronchi grating lines are perfectly straight. This was done with the help of microscope. The magnified view of Ronchi grating lines showed no deformations or other distortions so it was clear that I have got good quality Easytester eyepiece.

Looking through Ronchi grating eyepiece, some major aberrations can be inspected. But it is quite hard to test the parabolic (Nexstar’s primary mirror is f/2 spheric, secondary aspheric, but the whole system including the corrector plate should give the final result of parabolic curve) optics with such primitive way. As you can see from the next two images, the optics of my scope are quite good, though it is hard to judge the quality of the optics of such telescope that practically never reaches the thermal equilibrium.

In Focus                        Out Focus
As seen from these Ronchi photos, my Celestron Nexstar 11 GPS XLT scope has very smoothly undercorrected optics with the slight turned up edge issue. Keep in mind that the scope still wasn’t in thermal equilibrium when I have made those photos with DSLR camera (but it stayed outside for more than 3,5 hours).

But despite those very minor aberrations, the optical quality of the scope is surprisingly good.

Performance “in the field”

Planetary performance

I have tested the scope with extremely high magnifications… And when the weather was superb, I have observed the Saturn planet with more than 550X magnification. The huge amount of detail were visible during that impressive nigh (we had only 1 such night during the whole 2006 year): A, B, and even C ring was clearly visible as well as Cassini division was an easy target that night.. Two equatorial bands as well as some minor details were visible on the planet’s surface and the shadow of the planet falling to the planets rings added the final note.

Having the ability to observe planets using very high magnifications in really impressive weather conditions made me sense of how good Celestron optical quality really is.

Jupiter’s Great Red Spot and more than 10 cloud belts with some additional details could be observed at great weather conditions. If you observe Jupiter for more than half an hour, you can see how rapidly some of it’s surface details change positions or even disappear.

I had an ability to look at the Venus using blue filter at great weather conditions too. It was awesome to see some of it’s outer cloud structure, though it is always quite hard to observe Venus with the naked eye.


Moon is always fascinating even using low magnifications, but add the binoviewer and you will see how impressive our neighbour could be. You will really feel like your are looking at it from the space probe !!!

Planetary observation sessions could be really very impressive, so I think that you would be interested to know how this scope performs at deep sky objects.

Deep sky performance

At 11” of aperture, Nexstar 11 GPS light gathering possibilities gave an impressive results. All globular clusters are resolved to the core.

Famous “Ring” nebula showed it’s outer layers and the central star (but I saw it only 1 time during fantastic weather conditions from the very dark place), the Dumbbell nebula (M27) showed extended shape, Owl planetary nebula (M97) showed it’s “eyes”, Blinking planetary nebula showed it’s central star etc.

Galaxies, such as M51 (whirlpool), usually show spiral structure as well as the connection between the members… M31 galaxy core with outer dust lanes and companion galaxies could be observed with 2” wide angle eyepieces… Even the dust lane in NGC 891 could be easily observed in the dark place.

The Veil Nebula (the supernova remnant) shows tremendous amount of detail using UHC and OIII type filters…. Crescent nebula could be observed in the very dark site using UHC type filters too.

Even Flame and Horsehead nebulas can be observed without filters (though greatly recommended) during exceptional weather in pitch black observing place…

But none of the objects are so impressive as “the Great Orion” nebula in Orion constellation… Extended nebulosity and the complex structure adds more enjoyment viewing this diffuse nebula with binoviewer… 6 stars in trapezium region could be also visible during good weather conditions.

XLT coatings

I had an ability to test the whole system’s reflectance as well as it’s separate components. I can say that the results were very impressive. The reflectance of the primary and secondary mirrors showed almost the same results as Celestron has advertised (for XLT coatings) and Corrector plate showed even better light transfer results than manufacturer has advertised in their web-site. Our measurements were not as accurate as Celestron’s, but they have proved that I have one of the greatest optical coatings available today.

The light gathering capability is very important in astrophotography. As you can enter my own website, you can find some photos of nebulas, galaxies, comets etc. I have also tried to photograph the complicated Horsehead nebula with my non-modified Canon 350D DSLR camera using just 1,5 minute exposure time and was very surprised to see the nebula result in the LCD !!!

Celestron were always famous for their great optical quality, I must just approve that they are still holding it.

Mirror shift issue

In the earlier section of this comprehensive review, I mentioned that Celestron NexStar 11 GPS XLT scope use primary mirror focusing mechanism… Unfortunately, this solution is not a great idea for astro-photography. As I have DSLR camera, I also own the modified web-camera for planetary capture. And I should notice that my telescope’s primary mirror shift issue is quite annoying when using web-camera. I have approximately measured the amount of mirror shift in my scope when focusing planets, for example Saturn. If I put the planet into the center of my web-camera field of view and try to find the appropriate focus, the Saturn moves to the one side of FOV (when focusing) by the amount equal to planet rings diameter. That means that my scope has more than 40 arc-seconds of mirror shift.

It is more annoying in summer time, because the grease on the primary mirror baffle gets too sloppy. But as mirror shift issue is more relevant when using the web-cam, it isn’t as noticeable when using DSLR type camera for wider angle photos. The main action that I should make to avoid any mirror flop during longer exposures (when focusing the object with DSLR camera) is to finish the focusing routine by turning the focusing knob counterclockwise (the primary mirror then moves up and stays in place. Then it is less affected by gravity issue to move down a bit after focusing). But you will need a primary mirror lock feature (which is not available here, unfortunately) that will help you to capture different parts of the sky without need of refocusing objects every time you move your scope…

The summary of the optical quality of the telescope:

Pros:

  1. The out of focus star images are very near to perfection (when the optics reach thermal equilibrium) without noticeable aberrations
  2. Ronchi test showed only minor optical aberrations approving of the great overall quality of the optics
  3. Very impressive planetary details are visible during excellent weather conditions
  4. Excellent sharpness of the objects using very high magnifications during excellent weather conditions
  5. Great light gathering power gives the memorable, detailed observations of the dim objects
  6. Excellent optical system coatings improve the light gathering capability of the scope for both visual and photographic applications

Cons:

  1. Quite noticeable mirror shift (about 40 arc-seconds) is the annoying factor in photography
  2. The absence of the primary mirror lock feature adds additional refocusing procedures when trying to capture different astronomical objects during the same session

Mechanics and electronics

Mechanics

The mechanics of the Nexstar 11 GPS scope stands the today’s mass production standards. The quality of the internal parts of the scope, including motors, motor boards, cables and the whole assembly are very impressive. The ergonomics of the scope are really great. It is a heavy beast (for me), but precisely designed and made ergonomic handles always help me to get the scope to the field. You can always feel how good weigh is distributed when carrying you scope with both hands. Some other manufacturers should also think about such solution.

The scope has quality internal tooth gears that are made of bronze and all the other mechanical parts of the scope is really of good quality too, but the largest complaints can be addressed to the Altitude and Azimuth clutch systems as well as to the AC power plug (female type).

Alt-Az locking clutch

The Altitude and Azimuth locking clutches are made of the very fragile aluminum and I have heard many complaints about such locking solution. I have also mentioned that after more than 3 years my telescope’s altitude locking mechanism is starting to become too loose, so it is hard to lock the tube in altitude position without applying some pressure to the locking clutch. I know that sooner or later I will disassemble and separate my optical tube from the fork arms to get the ability to change that altitude clutch to the new one. Newer CPC models have the already modified clutch system and I hope they are absent of such problems.

AC power plug

This scope cannot work using internal batteries like some models of Meade scopes. It doesn’t have any battery compartment at all, so the only solution to feed the scope with the current is by using AC adapter or Powertank portable powerstation.

The major complaint belongs to AC power female plug, that’s installed to the Nexstar’s base. I have changed that female plug with the identical one, bought from the local electronics store. I do not know what type of plug does Celestron use, but the one I had previously installed by the manufacturer caused voltage variations and some powering off to the scope during the sessions. I thought that that may be caused by my Car adapter or Powertank battery, but when I found that a lot of Nexstar users have the same problem, I decided to change that female plug with the other one. I do not have any power issues since then…

Slip ring system

You will never come across the cable warping problem when using this scope visually. It has internal slip ring system that eliminates any hanging power cables issue. If you are planning to use this scope visually as it is, just adding more eyepieces and other visual accessories, then I can assure you that you will not have any cable warping issues.

However, the slip ring system has it’s disadvantages as well. There is the output power plug (female type) in the base of the Nexstar scope (along with the other ports). Never plug inn the device to this port, which will draw more than 0,5Ah current. The slip ring system will be additionally loaded with current and that could damage it’s contacts.

So there are only few devices that can be plugged to that AC output port. Forget about using heater strips and even complex focusing mechanisms with this port and better use the other Powertank’s battery 12V output port.

You will find 4 additional ports for accessories in the base of the NS11 GPS scope:
  1. PC port
  2. Aux device (Hand control Unit can be plugged-inn to that port)
  3. Aux device (Hand control Unit can be plugged-inn to that port)
  4. Autoguide port
PC port allows the scope to be controlled through PC or Laptop.

Prior to use the planetarium program with the scope, be sure that you have downloaded the latest Ascom drivers.

The Celestron’s Nexremote software can be used with the scope connected through this port to the computer as well.

Aux ports can be used for Hand Control Unit operation (I you do not want to use it plugged in the Fork arm’s port) as well as for some future devices.

Autoguider port is a great component for CCD camera owners. CCD astronomical imaging camera can be plugged in this port and act as the autoguider. If you would like to plug and use your modified web camera as the autoguider, you will need to buy or make the additional relay box for this NS11 GPS autoguider port.

Performance and software

GPS alignment

Using the Nexstar in the field is a great joy even for newcomer amateur. But I should mention that setting up the scope for the newcomer is not an easy procedure however. It could be hard to align the scope. As I am the person who knows the sky pretty well, alignment process is very quick procedure for me, but if I were the newcomer – then I would have had more problems in the field during scope set-up routine.

During GPS alignment procedure you are told to center the desired star in the finder scope, and then in your eyepiece. Everything seems to be clear, but the problem becomes more apparent when you try to understand which star is the brightest in the viewfinder. During alignment procedure the scope never puts the alignment star in the field of view of the viewfinder, so it is hard (for newcomer) to understand which star should be centered. This issue was solved when Celestron offered it’s patented Sky-Align feature. But as I’m familiar with the sky objects and brightest stars it has never been an issue for me.

The Go-To accuracy is quite impressive and you will always get the object into the field of view of your 15mm eyepiece after good alignment.

EQ mode

As I’m taking some photos, the equatorial mode is more important to me than Alt-azimuth. I should commend the Celestron of their great software solution when using scope in EQ mode. Celestron offers fast and quite accurate EQ-North alignment feature so you can be sure you have aligned your scope to the true North.

For EQ-North users, you are asked to move your scope to Index position and then press Enter. Then handpad software asks to move the scope towards meridian. After pushing Enter, the software will ask you what kind of Alignment method you would choose (I usually use Auto Two Star Alignment). The scope moves to one chosen star, asks to center it in the Finderscope, and then in the eyepiece… And then it moves to the other star and ask to make final alignment.

After “Alignment Success” report on the screen of the Handpad LCD, you should go to the Utilities menu, find Wedge align feature and activate it. After proceeding the Hadpad instructions you will go back to the alignment procedure again. Make the alignment one more time and you are ready to capture the sky !!!

My tip for even greater EQ alignment accuracy would be to repeat Alignment and Wedge Align routine for 3 times. Then you will be really very close from the real celestial pole.

Tracking performance

The scope’s tracking capability is really great in Alt-Az mode, but it gets worse in EQ mode. I can take photos (using Canon 350D DSLR camera and F/6.3 focal reducer) with the maximum exposure time of 1 minute only. If I go longer – the periodical error as well as random errors become very apparent and always spoil my exposition results. I have tried to record and then playback the PEC corrections to the hand control software (I have the latest firmware), but the results haven’t improved at all.

I have recently tried to Autoguide my scope using additional guidescope, and the results showed the 20-25 arc-seconds Peak to Peak periodical and random errors. Keep in mind that such scopes cost much less that some mounts only, so the tracking accuracy is quite good and if you can afford some autoguiding solution, then you will get excellent results with DSLR or large chip CCD cameras.

Backlash issue

I do also have some backlash issue when using the scope both visually and photographically. Some free play among worm and tooth gears are always present whatever mount you will take, but it is always annoying issue for deep sky photography using auto or self guiding solutions. The backlash of my scope is in medium range, but thanks to the handpad software that helps to cope with this issue.

Hand Control Unit software

The software of the Hand Control Unit can be estimated as good, but not great.

The main disadvantage for the software can be addressed to it’s object databases. If you are looking to some catalogs object or so, you will not be informed that this object has cross-referenced name on other catalogs as well. Only most popular “Messier” catalog objects have additional “NGC” identification number as well.

You cannot filter objects by constellation, or use the advanced nearby object identify function as well. These features were added to the newer hand control units that came with CPC scopes.

There are no comet and asteroid databases in the handpad unit software at all. If you want to observe the comet, you should manually consult Internet sources for the object coordinates, and then add them into the handpad unit software as “User Object “or as “Ra.” and “Dec.” coordinates.

There is no artificial satellite tracking software as well. Meade telescopes hand control units have both, comet, asteroid and satellite tracking databases. You can easily download the latest updates from the internet and stay updated with the object database all the time. However there is no such solution available in the Celestron’s Nexstar hand control unit at all (the newer handpad models that come with the CPC scopes, already has the Internet software download feature, but still lacks comet, asteroid and artificial satellites database).

The other hand control unit software issue is addressed to the PEC tool. When you are making the playback of your recorded corrections, you cannot go back to the index menu or use object search database. If you push UNDO button in order to go back to the other menu, the PEC playback will be turned off automatically. This issue is already solved with the never hand control units.

In conclusion about the software I can say that I am quite satisfied about the hand control unit and it’s software. I can always get more features using third party astronomical software and some lack of the features are a bit disappointing but really not the huge disadvantage in all.

Pros:

  1. Excellent fit an finish of the internal parts, electronics and cables.
  2. Great scope ergonomics makes it quite easy for transportation.
  3. Internal slip ring system eliminates the cord warping issue.
  4. Bronze tooth gears, other quality parts.
  5. 4 additional ports for other accessories.
  6. 12V AC out power outlet.
  7. Easy alignment routine (for advanced users).
  8. Impressive EQ alignment routine.
  9. Great tracking performance for visual observation in Alt-Az mode.
  10. Very good go-to performance.
  11. Periodic Error Correction feature.
  12. User friendly Handpad software.

Cons:

  1. Alt-Az lock clutch problem. Design flaws.
  2. No internal battery compartment.
  3. Poor AC input female plug.
  4. Power output plug in the base of the scope is restricted (because of slip ring system) to 0,5A loading capacity.
  5. Alignment procedure is quite easy, but the scope never puts the alignment star in the field of view of the finderscope, so it’s hard to say which star is the brightes in the field (for newcomers).
  6. Mediocre tracking performance in EQ mode.
  7. Noticeable Periodical Error. Limited exposures to 1 min (using f/6.3 reducer/corrector).
  8. Noticeable backlash, free play between the gears.
  9. Mediocre hand control unit object databases.
  10. No object filtering features (except filter and slew limits).
  11. Cannot use other scope features and utilities during PEC playback routine.


Recommended accessories

These are the optional accessories that I would highly recommend for this scope:

  1. Rechargeable power supply unit and 12V Car compatible power cable (If you are planning to travel with your scope)
  2. Dew-shield is highly recommended during observation sessions to get rid of the dew formation on the corrector lens. If you live at the humid area, additional dew-heater with controller could be used during observations.
  3. Get the optional eyepiece kit. Take your choice for good 1,25 and 2” eyepieces. Is is always great to have both planetary (lower focal length) and wide angle deep-sky (higher focal length) eyepieces. Don’t forget about 2”, high reflectivity prism either.
  4. Additional UHC and/or OIII filters will definitely enhance your views of the nebulas
  5. Get a 3D-like views with your both eyes using binoviewer
  6. Deep-red flashlight will definitely help you in the dark.
  7. Good CCD camera would be great choice for astrophotography sessions, but you can get a modified-web camera or even DSLR for the first steps
  8. Reducer-corrector lens (f/6.3) will give you flatter wider-angle field and reduce your exposure time.
  9. Sturdy Equatorial wedge is necessary for deep-sky photography
  10. Additional Scope-guider or Radial guider will help you to cope with some mount tracking errors (optional counter-weight system is recommended for precise balance of the tube)
  11. Focusing mask will help you to find the best focus quickly. You can make it by yourself.
  12. Additional zero-image shift focuser would help you to cope with some mirror shift issues.
  13. And, finally… Get the star atlas… In case you will need some consultations !

Summary

This scope is the great instrument for beginners and amateur astronomers. Quality optics, good Go-to operation and great ergonomics makes the observation as easy as it could be, despite some issues.

I will definitely recommend this scope for first astrophotography steps. Add some additional equipment and this scope will become even serious observatory instrument with lots of capabilities.

Clear skies !
Lukas Jonaitis.





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