Review of the Celestron 4SE Maksutov Cassegrain Telescope

ITEM
Celestron NexStar 4SE Telescope

DATE PURCHASED
December 2010

MANUFACTURER
Celestron Corporation
2835 Columbia Street
Torrance, CA 90503
USA

PRICE (2012)
$500 USA
£460 UK
€450 EuroZone

GENERAL FEATURES

* 4 inch (102mm) Maksutov Cassegrain telescope
* Celestron’s StarBright XLT high transmission coating
* StarPointer (red dot finder)
* Internal flip mirror
* Quick release fork arm mount, optical tube, and accessory tray
* Computerized Altazimuth mount
* Internal battery compartment
* 1.5 inch (38.1mm) steel tripod with a built-in wedge

COMPUTERIZED MOUNT FEATURES
* 38,181 object database with 200 user-definable objects and expanded information on over 200 objects.
* NexStar SkyAlign (alignment using three bright celestial objects with no need to know their name)
* Flash upgradeable hand control software and motor control units for downloading product updates over the Internet
* Programmable DSLR camera control
* DC Servo motors with encoders on both axes
* Double line, 16-character Liquid Crystal Display Hand Control with backlit LED buttons
* NexRemote telescope control software and RS-232 cable included for advanced control of your telescope via computer
* GPS-compatible with optional SkySync GPS Accessory

CELESTRON NEXSTAR 4SE SPECIFICATIONS

Telescope OTA
Optical Design: Maksutov-Cassegrain
Aperture (mm): 102 mm (4.02 in)
Focal Length (mm): 1325 mm (52 in)
Focal Ratio: f/13
Finder: Red Dot Finder
Star Diagonal: Internal Flip mirror
Optical Tube: Aluminum
Highest Useful Magnification: 241 x
Lowest Useful Magnification: 15 x
Limiting Stellar Magnitude: 12.5
Resolution (Rayleigh): 1.37 arc seconds
Resolution (Dawes): 1.14 arc seconds
Light Gathering Power: 212 x
Angular Field of View (deg): 1 °
Linear Field of View @ 3000 feet (914 meters): 53 feet (16 meters)
Secondary Mirror Obstruction: 1.38 in (35 mm)
Secondary Mirror Obstruction by Diameter: 34 %
Secondary Mirror Obstruction by Area: 12 %
Optical Coatings: StarBright XLT
Optical Tube Length: 34.3 cm (13.5 inches)
Optical Tube Weight (without Mount and Tripod): 2.5 kg (+/- 0.1 kg), 5.5 pounds (+/- 0.33 lb)

Mount, Tripod, Hand Controller
Type: Single Fork Arm Altazimuth
Power Supply: 12 vdc center pin positive (exterior supply) or 8-AA batteries (internal supply)
Payload Capacity: 10 lbs (4.54 kg)
Dovetail Compatibility: Vixen Dovetail
Mount Weight (without OTA and Tripod): 2.9 kg, (+/- 0.1kg), 6.4 pounds (+/- 0.33 lb)
Slew Speeds: Nine slew speeds: 4°/sec, 2°/sec, 1°/sec, 64x, 16x, 8x, 4x, 1x, .5x
Tracking Rates: Sidereal, Solar, and Lunar
Tracking Modes: Alt-Az, EQ North & EQ South
Azimuth Mount Alignment Procedures: SkyAlign, auto two star align, one star align, two star align, solar system align,
Equatorial Mount Alignment Procedures: EQ auto two star align, EQ one star align, EQ two star align, EQ solar align
Precise Polar Alignment: Any Star Polar Alignment
Software Precision: 24 bit, 0.08 arcsec calculations
Communication Ports: RS-232 communication port on hand control, Aux port, Camera Control port
Computer Hand Control: Double line, 16 character Liquid Crystal Display with 19 fiber optic backlit LED buttons
Database: 38,181 accessible objects
Software Features: Camera Control
Other Equipment: Camera Shutter Cable
Software: NexRemote V1.6.14 & "The Sky®" Level 1
Tripod: Steel with built-in wedge, 1.5 inch (38.1 mm) primary legs, 1.0 inch (25.4 mm) extension legs
Tripod Weight with Wedge (without Mount and OTA): 4.5 kg, (+/- 0.1kg), 9.9 pounds (+/- 0.33 lb)
Total Weight; Telescope, Mount, and Tripod with Wedge: 9.9 kg, (+/- 0.3 kg), 21.8 pounds(+/- 0.99 lb)


REVIEW: (Note: The 4SE and 5SE telescopes use the same identical mount and tripod.)

1. Packing for Shipping.

I did not make measurements of the shipping container’s size. The telescope comes in one huge box made of heavy duty cardboard. Open the box and you find another box, thin cardboard covered with photographs and descriptions of the telescope and its capabilities. Remove the second box and you come to another heavy duty cardboard box. Open it and you are into the sturdy, foam, form-fitted, packing. The shipping box was so large, I had to lower the rear seats as well push the front passenger seat all the way forward and insert the box into my car, a Toyota IQ, from the rear hatchback. Without the hatch back, I would have needed to remove the telescope from the shipping boxes to get it in the car.

2. Assembly.

The telescope comes in three parts, tripod, telescope attached to the mount, and accessory pack. Included is a four page getting started guide. Scope assembly is simple and intuitive; Remove the tripod, telescope and accessories from the shipping box. Open the tripod legs, attach the mount to the tripod using three thumb screws that are permanently fixed to the tripod, tighten the center brace hand nut, and slide the red dot finder in the mounting saddle attached to the telescope. Open the top of the azimuth base, install 8 AA batteries, align the red dot finder, and the scope is ready to go. The accessory pack includes a 25mm E-lux 5 element Plossl, one camera control cable, one RS 232 computer cable, one bubble level, and one spanner wrench for tightening tripod bolts if needed.

3. Telescope Components.

a. Manual

i. The NexStar 4/5 SE programming is very robust and feature loaded. The manual, while thorough, is not adequate in many key areas. Photographs and drawings of non-related equipment are sometimes used for illustrations. This is very confusing, especially for functions related to operating the telescope mount in the equatorial mode. For example, drawings of the original C8 are used to demonstrate how to align the mount in the polar position when using a wedge. This drawing has no semblance to the 4SE at all. No addendum is provided to cover major changes in the hand controller programming or a simple notification that the hand controller programming is modified in major ways.

ii. The manual in several places has conflicting information such as explaining the capability to program and control digital SLRs then recommending that the user buy a used film camera for photography. The film camera part is obviously a cut and paste from an ancient 20th century catalog as are the illustrations for polar alignments, around the early 1980s. The manual in several places mentions using the mount for photographing deep space objects but at the end of the manual, almost hidden, is the lawyer protection statement; photography for solar systems objects only. The manual goes to some effort describing a wedge polar alignment routing that is located in the Utilities Menu. However, Celestron no longer has the wedge polar align routine programmed in the hand controller. Instead it has its Any Star Polar Align programmed in the hand controller. This routine is located in the Align Menu but only appears after an equatorial alignment has been successfully completed.

iii. A beginner will be overwhelmed by the amount of information in the manual that is needed to explain the numerous features of the mount and will need to keep the manual at the ready for a while. Fortunately for beginners, the Celestron NexStar Three Star alignment works as advertised and is well explained in the manual. Simply point the telescope at three bright objects and the alignment is done. This lets a beginner very easily get started then slowly dig into the depth of the telescopes capabilities.


b. Tripod.

i. Celestron uses essentially the same tripod for its entire SE series. The only difference is the tripod heads. The 4SE as well as the 5SE tripod has a built in wedge and weighs one pound more than the tripod used for the larger 6 and 8 SE. The small lightweight 4SE benefits greatly being supported by essentially the same tripod used to support the much larger and heavier 8SE.

ii. The tripod’s primary legs are made of stainless steel tubing and have a diameter of 31.8 mm (1.5 inches). The extension legs are also of stainless steel tubing with a diameter of 25.4 mm (1 inch). Tube thickness is unknown but substantial. The tripod head, equatorial wedge, and tripod leg center brace are made of aluminum; however, the tripod head leg sockets are made of a very hard plastic material as are the extension leg sockets and extension leg tips. The extension leg tips have a rubber coating to control vibration.

iii. Each extension leg socket has a thumb screw to tighten the extension leg in place. The plastic extension leg socket has a threaded brass insert for the thumb screw. An equatorial wedge is built into the tripod. Wedge set-up is simple; loosen one screw and tilt the base to the desired angle, then tighten the screw. This can be done with or without the telescope mount attached and no tools are needed. A graduated indicator marked in 5 degree increments provides some guidance.

iv. Fit and finish of the tripod are excellent. All parts are well machined or cast to very tight tolerances. No slop was observed in any of the moving parts. No bolts needed tightening. During operation of the telescope, no vibration was noticed when focusing the telescope, reaction to brisk wind gust, or accidentally bumping the telescope or tripod. Vibration induced by forcibly tapping the eyepiece dampened in about a second.

v. The only negative with the tripod is that no mechanism is provided to make the fine adjustments in azimuth or altitude needed to obtain a precise polar alignment needed for unguided short exposure astrophotography.

c. GOTO Azimuth/Equatorial Mount.

i. The mount has ten alignment processes. All but the EQ Polar Align are clearly explained in the manual. All alignment commands have help functions programmed in the hand controller that explains each alignment process step by step.

* Azimuth Commands
o Sky Align
o Auto Two Star Align
o Two Star Align
o One Star Align
o Solar Align
* Equatorial North or Equatorial South Commands
o EQ Auto Align
o EQ Two Star Align
o EQ One Star Align
o EQ Solar Align
o EQ Polar Align (computerized routine to obtain a precise polar alignment for the mount).

ii. The NexStar 4/5 SE mount is very versatile. It is usable as either an azimuth or as an equatorial mount and can be mounted on a tripod or used as a table top telescope. For operation in the table top mode, the mount rest on three vibration absorbing rubber feet built into the base of the mount. To transform the mount from the azimuth mode to the equatorial mode, simply loosen a toggle bolt, tilt the telescope to the desired angle, then tighten the toggle bolt. Do an equatorial alignment, then a polar align followed by replacement of the alignment stars. The polar alignment is only moderately effective as the telescope mount must be manually moved in azimuth and adjusted altitude to obtain a precise polar alignment. No fine adjustment controls are available to do this task; thus, a precise polar alignment is a matter of chance only and not precise enough for astrophotography.

iii. Mount alignment is fast and easy. Celestron’s Sky Align is excellent (any three bright objects no need to know their name). The alignment objects should be 60 degrees apart, not near the zenith, nor near the horizon. Planets can be used but also can be problematic if they are close to a bright star as the mount can confuse the planet with the star. The moon is simply too large to properly center it in the eyepiece. The other alignment processes also work very well and are easy to do. In the equatorial mode (north or south), the mount has an EQ Auto Alignment that works very similar to the Sky Align; point the telescope at any two bright stars, no need to know their name.

Regardless of the mode (azimuth or equatorial), the accuracy of the alignment is dependent upon how well alignment stars are centered in the eyepiece and how level the mount is. The accuracy provided by a level mount is only needed for tracking when doing astrophotography work. For visual viewing the mount will provide accurate gotos and tracking without a level mount.. eyeball level is more than good enough.

iv. Mount slews are audible but not noisy … louder than a SkyWatcher SynScan AZ GOTO, slightly quieter than an iOptron NOVA GOTO mount, and substantially quieter than a Meade DS2000 mount. In the tracking mode, the mount is essentially silent with a faint ticking noise heard from time to time.

v. GOTOs in both the azimuth and equatorial modes are accurate; within the center third of the eyepiece with a 25 mm eyepiece and frequently within the center third of a 12.4 mm reticle eyepiece.

vi. The hand controller programming is loaded with features which make the NexStar 4/5 SE mount a very powerful tool for astronomy and for photography including controlling a digital SLR. The shear number of features are far too many to list in this review without writing essentially most of the telescope’s manual. For anyone interested in the features of this mount, download the manual from Celestron. While the features are numerous and useful, they are far too many for the mount’s 19 key hand controller to easily accommodate which results in nesting of commands and some commands located in non-obvious locations. Key controls like the up and down button are located on the numerical part of the key pad which can be confusing for people experienced with Meade, iOptron, or SkyWatcher hand controllers. Celestron clearly needs a hand controller with a couple more keys for this telescope. The addition of a red led lamp would also be welcomed. Note: in 2012, Celestron started shipping the 4SE with its new handcontroller which addresses many of the above issues.


vii. The fit and finish of the mount is excellent. Parts are made to tight tolerances and, other than the plastic hand controller, battery cover, and dovetail cover shroud, are made of metal. Unlike many goto mounts, both azimuth and German equatorial, the 4/5 SE mount's dovetail saddle has a large friction plate that grips the telescope’s dovetail providing a firm and secure grip on the telescope.

viii. The hand controller fits into the altitude arm of the mount for storage. It is easy to remove and replace in the dark of the night. The hand controller seems light and flimsy in comparison to hand controllers of other manufacturers. Some programming is confusing such as the need to punch enter followed by align for each alignment star or having to first do a goto to a suitable star before using the AnyStar Polar alignment or replacing an alignment star. The hand controller fits loosely in the altitude arm and is more than adequate for the azimuth mode. However, in the equatorial mode, the hand controller can become loose and fall in some positions of DEC as the hand controller is in effect up side down. For either mode, equatorial or azimuth; the length of hand controller cable is on the short side of adequate. Another 6 inches (15 cm) would be a bit more ergonomic. However, there is not sufficient space to accommodate a longer cable with the hand controller mounted in the altitude arm. In my opinion, the hand controller mounted in the altitude arm is more of a pretty design feature than a useful one.

ix. The mount tracks very accurately in either the azimuth or equatorial modes with the image appearing to remain stationary in the eyepiece for hours. In the equatorial mode, the mount can track steady enough to support unguided exposures times between 45 and 90 seconds. (NOTE: These times are not achievable with a stock 4/5SE mount. To obtain the precise polar alignment needed for photography, the latitude adjustment bar must be modified.)

d. Celestron NexStar 4 SE OTA.

i. The optics of the 102 mm f/13 Maksutov telescope are excellent providing crisp and sharp views even at high magnification. With a 32mm eyepiece, it provides surprising views of deep space objects like star clusters, double stars, etc. Nebulae and galaxies are without detail. This little MAK could easily function as the only telescope for someone with developed observing skills who requires a very portable telescope. The telescope is factory collimated and mine is still collimated going on two years of usage based upon a star test (Polaris) at 440x (6mm eyepiece/2x barlow). The optical performance of the 4SE is on par with that of a well collimated C6S and my Meade 2045LX3 102mm SCT (note: my 4 inch SCT was extensively reconditioned and has above average performance for this noted Halley Scope).

ii. The fit and finish of the telescope optical tube are not as they should be. Noticeable mirror shift occurs while focusing and the focus knob wobbles. On the other hand, only a light touch is needed and achieving a fine focus is easy. The use of an integrated flip mirror back places a severe restriction on the OTA. It must be used with a single arm mount with a tine on the left side as the eyepiece is not rotatable to allow for its usage on a German equatorial mount or the right side tine mounts made by Celestron and other manufacturers. The red dot finder has a variable intensity control and is well made. The finder is adequate for its task to find alignment stars; however, it is not adequate should the user want to manually find objects.

e. Reliability: Note this section is based upon a sample of one. As any statistician will tell you, it is valid only for the one sample (my 4SE) and is not statistically valid for the whole population (all 4SE telescopes). I suspect that my 4SE is what the automotive world calls a “lemon.” I have experienced four failures with my 4SE. In each case, I elected self-repair instead of warranty work.

i. My first failure was the altitude drive motor. This failure occurred about two months into my use of the telescope. At that time Celestron was selling spare parts for the 4SE and, since the motor was very inexpensive… much less than shipping for warranty work for me (Greece to Germany) … I purchased two motors from Celestron, a replacement motor and a spare. Replacing the drive motor is easy but the prudent person will take notes and photographs … especially of cable connections. The replacement motor performed well but exhibited some of the same characteristics exhibited by the original motor (speed variations and slow starts). About 6 months after the motor replacement, the altitude drive motor failed again. I replaced it and now 9 months later everything seems to work very well. The altitude drive motor sounds very similar to the azimuth drive motor and exhibits none of the quirks that the two motors that failed exhibited (speed variations and slow starts).

ii. The camera control feature of my mount stopped functioning. I noticed this when the telescope was over one year in use. Since I don’t use the function I really don’t know when the failure occurred. The problem was a cold solder joint and the one wire involved was detached from a socket in a circuit board. The repair was simple.

iii. After about one and a half years of usage, the power switch for the 4SE mount stopped functioning. Again, the problem was a cold solder joint for one of the switch’s leads. Again, a simple repair.

4. Conclusions:

a. Overall. The 4SE is an excellent telescope; well designed and built with good optics. It performs very well for a 102mm aperture telescope. The mount and programming have many advanced features making it a very versatile scientific instrument. The telescope is ideal for a beginner who wishes to explore all aspects of amateur astronomy, including astrophotography. It is an ideal portable observatory for advanced users who want a small, light-weight, telescope that is capable of handling a variety of tasks.

b. Visual Observation.

i. The 4SE is an excellent telescope for viewing solar system objects. For typical viewing conditions where magnification is limited by atmospherics, it competes head on with a larger C6S for the moon, surface details of Jupiter, and even the trapezium in Orion.

ii. For deep space, its sharp image helps some to resolve stars in globular and open star clusters but it definitely can not compete with a larger150mm SCT. With little exception, nebulae and galaxies are small gray smears of light with no definition as typical in most small aperture telescopes. In moderately light polluted skies (the Milky Way is visible but with no details and only two stars of the Little Dipper’s bowl are visible), the connecting star field between the two galaxy cores in M 51 is fleetingly visible with direct vision. I have never observed with the telescope in dark skies. Its views are much more likely to be appreciated by an experienced observer than by new comers to astronomy who have yet to develop their observational skills.

c. Astrophotography. Celestron advertises the 4SE as a telescope suitable for astrophotography including imaging deep space objects. While Celestron does have a “solar system only” disclaimer buried deep in the back of its manual, the disclaimer is not obvious and ignored in advertisements of the telescope. This astrophotography section is included to answer the question, is the 4SE usable for astrophotogrphy? The answer is a sort of yes but with a big BUT and major limitations …. No guided long exposures …. a potential for unguided short exposures ….. and good for unguided very short exposures.. .

i. The 4SE mount has a built-in wedge and Celestron’s Any Star Polar Alignment routine to provide for a precise polar alignment. It also has a routine, “Calibrate GOTO,” programmed into the hand controller that will measure and adjust for the impact of adding a heavy load such as a digital single lens reflex camera to the back of the telescope. The Calibrate GOTO command does maintain the accuracy of the 4SE mount and GOTOs with a camera and focal reducer attached to the scope remain accurate. From the perspective of being able to handle the additional weight of a DSLR, the 4SE is capable of photography.

ii. For photography in the Azimuth Mode. The 4SE mount provides a sturdy platform. Exposure times are generally limited by field rotation, not mount movement or vibration. The mount is capable 30 second exposures with a 30% rejection rate due to mount movement, star trailing, vibration, etc. even with conditions of moderate wind. This is more than adequate for very short exposure astrophotography (exposures of 30 seconds or less).

iii. For photography in the Equatorial Mode. Out of the box, the 4SE can not be used in the equatorial mode for astrophotography. Also, in the equatorial mode, the 4SE is sensitive to wind conditions.

* The 4SE mount has a fatal flaw, no mechanisms exist for fine adjustments in azimuth or altitude needed to precisely polar align the mount. This is true whether or not a drift alignment is used or Celestron’s Any Star Polar Align. A modified latitude adjustment bar is easily made using hand tools that will allow for a precise polar alignment. With a modified latitude adjustment bar, the mount with some effort and a little luck can be precisely polar aligned. If care is also taken to level the mount and to precisely center alignment stars with an 12.4 mm or shorter reticle eyepice, the 4SE mount can typically provide 45 to 60 second unguided exposure times with approximately a 60 to 70 percent retention rate with no wind. The retention rate drops under windy conditions. The 4/5SE mount is not capable of long-exposure, guided work. Here is a link describing the modified Latitude Adjustment Bar: http://www.astronomyforum.net/celest...tment-bar.html

* Due to the difficulty of obtaining a precise polar alignment, even with the modified latitude adjustment bar, maximum attainable exposure times will vary between photographic sessions. The maximum exposure time I have obtained with the 4SE was 180 seconds one session but I have never been able to repeat this time. Exposures of 120 seconds have been obtained two times and 90 seconds fairly often. However, exposure times of 45 to 60 second are typical in conditions with no wind. Guided long exposures are not possible and unguided short exposure work( 60 seconds or more) is not practical.

* As in the azimuth mode, the 4SE in the equatorial mode is suitable for unguided, very-short exposure photography, albeit with significantly longer exposures than possible in the azimuth mode. Without the capability to do guided long exposure work, the potential of the 4SE for photography is limited to the brighter deep space objects.

iv. The 4SE mount in the equatorial mode eliminates the impact of field rotation from the photographic process. This has several significant impacts that can increase the quality of the final image as well as make the 4SE mount superior to an azimuth mount for photography:
* Exposure times are longer which increases the signal to noise ratio of each exposure,
* If an object is not centered in the field of view, less information is lost due to fanning by stacking programs as they adjust each frame for field rotation.
* Photographic sessions can include objects high in the sky where the atmosphere is the thinnest and the impact of light pollution less.
* Photographic sessions can be longer as they must not be terminated for objects high in the sky as they approach the meridian.

v. The 4SE can control a DSLR. The hand controller can be programmed to photograph up to nine objects controlling the number of exposures, the duration of each exposure, and the delay time between exposures. This programming is cumbersome in that an actual goto must be done for each object. Once the sequence is started, the process is automatic until all objects in the program have been photographed. The only advantages over an interval timer are that exposure times can be varied, and the controller will automatically go to another object once a photographic sequence is completed. Neither of these two advantages is significant. I find an interval timer is much easier to use and no longer use the mount’s camera control feature.

vi. The 4SE is a 102mm f/13 Maksutov Cassegrain Telescope and its high focal ratio is not particularly suited for very short exposure photography. With very short exposures, the images produced have a very low signal to noise ratio. The typical method to adjust for a high focal ratio telescope by extending exposure time is not available for very short exposure photography with exposures of 60 seconds or less. A 0.63 focal reducer reduces the focal ratio to 8.2 and increases the signal to noise ratio. A focal ratio of f8.2 is still slow but acceptable. Increasing the number of frames that are stacked also helps to some extent but the effectiveness of stacking markedly decreases after 20 to 30 frames. I typically like to get at least 150 exposures then use only the best exposures for stacking. This is true whether or not I am using the 4SE OTA or my 4 inch SCT on the SE mount for photography.