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Home / Post Mortem of a Celestron Firstscope 114
by Daniel W. Rickey, Ph.D. 06/22/03 | Email Author


Figure 1. The Celestron 114 Firstscope on its equatorial mount. The Celestron name is in red and is painted on, i.e., it is not a decal. Note the size of the optical tube in comparison to the mount.

Introduction

This review, like many other reviews, is of a used telescope with unknown history. This particular example (shown in Figure 1) was purchased from a pawn shop sight-unseen and had previously suffered: there were scratches and dents on the optical tube, the optics were quite dirty, and some screws were missing. Consequently, this particular example may not be representative of this model.


Figure 2. The specifications are given on this label. The “f1” on the label is likely meant to refer to “focal length”. The scope is actually an f/8.

The only documentation supplied is the label shown in Figure 2. The 910 mm focal length is a bit unusual (most are 900 mm) and helped to identify the scope. An advertisement in a 1996 issue of Astronomy list two variations: the Firstscope 114 and the Firstscope 114 Deluxe. The deluxe model replaced two 0.96” eyepieces and a 2X barlow with two 1.25” eyepieces and no barlow. The example reviewed here is the deluxe model. The same ad gave the price as $250US (one assumes for the non-deluxe version), which corresponded to about $375 CND. The deluxe model would likely have been over $400 CND.

The Mount

The mount appears to be identical to current “EQ2” equatorial mounts that are popular on low-cost telescopes. However, instead of aluminum legs, this example has wooden tripod legs that are of respectable quality.

As received, the equatorial head had a great deal of slop in it and was not usable. In order to correct this problem, the mount was disassembled (see Figure 3). Most of the moving components were covered in a very thick and sticky grease that was about the consistency of gluestick. One assumes that the purpose of this grease was to remove some of the play in the mechanical components.


Figure 3. Photograph showing the mount disassembled for inspection.

In order to polar align the telescope, the mount allows motion about the vertical (azimuth) axis. This axis had a great deal of play in it and allowed the telescope to wobble during normal use. Figure 4 illustrates that this axis comprises a conical stub shaft that fits into a similarly shaped hole. The black paint on the mating surfaces of the two pieces is very unusual since it quickly wears off and mixes into the grease. The clearance between the shaft and hole was measured using feeler gauges, shown in Figure 5, and was found to be 0.51 mm (0.020”). The base was assembled and the corresponding wobble measured as shown in Figure 6. The clearance is 0.76 mm (0.030”), which corresponds to a wobble of plus and minus 0.55 degrees.


Figure 4. Photograph showing how the mount’s base fits together.


Figure 5. Photograph showing measurement of the clearance between the shaft and hole.


Figure 6. Photograph illustrating how the wobble was measured using feeler gauges. In this case the feeler gauge is 0.76 mm (0.030”) thick.

There were a number of other problems with this mount. For example, Figure 7 shows that the mount is made from very thin aluminum that has broken once. To lock the right ascension axis, a steel screw presses against the RA gearshaft. Figure 8 shows how the softer aluminum gear shaft is being worn by the much harder steel screw. The RA slow motion control was very stiff in part of each rotation and was likely due to a out-of-round worm gear. In addition, the counter weight shaft is locked in place by three screws as shown in Figure 9. These screws are destroying the threads on the declination axis as well as their own threads.


Figure 7. Photograph showing the underside of the mount. The casting is very thin aluminum (about 3 mm at green arrows) and has already broken (red arrow).


Figure 8. Photograph showing the cast aluminum right ascention gear. The red arrow is where the RA lock screw is scoring the shaft, and the green arrow shows the resulting aluminum filings.


Figure 9. Photograph showing how the counter weight shaft is held onto the declination shaft. To prevent loosening, three screws are threaded up against the declination shaft’s threads, which are being destroyed (green arrow).

The optical tube

The tube is made from very thin aluminum, which dents rather easily. However, it is fairly light weight. One quirk is the manner in which the secondary mirror is supported (see Figure 10). It is held by a single plastic arm, instead of the usual spider, and its location cannot be adjusted. Another quirk is that a clip covers part of the secondary mirror.

The tilt of the secondary mirror is adjustable via three small screws shown in Figure 10. The primary mirror has three spring-loaded thumb screws for adjustment and these function quite well. The focuser is made of plastic and uses two screws to lock the eyepiece in place.

A small finder scope is made of plastic and is heavily stopped down. It has an adjustable focus. Its mount uses two rings and six screws to securely hold the scope in alignment.


Figure 10. Photograph showing the single arm secondary mount. The green arrow shows a clip that obscures part of the secondary mirror. This telescope accumulated a fair bit of dust during its stay at the pawn shop.

The Eyepieces

The two included eyepieces shown in Figure 11 are the deluxe ones with 1.25 inch barrels.


Figure 11. Photograph showing the two 1.25 inch eyepieces included with the deluxe model. Fit and finish are evident.

Performance

At some point in the past the finder scope had been bumped, which caused the thin aluminum optical tube to dent. Consequently the finder scope could not be properly aligned. In any event, the finder scope was too small to be useful.

Although the mount performed much better after being cleaned and adjusted, polar alignment was out of the question. Two lock knobs allowed the telescope to be slewed by hand. Once aimed, tightening these knobs caused a change of direction and required correction with the slow-motion controls. Once tightened, the scope could easily be rocked a better part of a degree. Turning either slow motion control induced an annoying shake.

The focuser is a bit stiff but was otherwise acceptable. Unfortunately any attempt to focus caused large-amplitude low-frequency oscillations, which tended to induce motion sickness.

The telescope was aligned with a laser collimator before visual testing. Optical performance was acceptable (for a telescope in this price range) with no gross defects. The clip covering part of the secondary mirror was visible in out-of-focus images.

Discussion and Conclusion

When reviewing a telescope, an important criteria is the overall design and construction of the instrument. Ideally no single component will be the limiting factor of performance. For example, in a high-end telescope every component will be of the highest quality and observing will never be limited by the quality of the instrument, only by the inherent resolution and viewing conditions. Entry-level telescopes are a different matter: ideally the telescope will be easy to use and the observer won’t be frustrated by mechanical problems. Optical quality is less of an issue because beginners are usually happy with less than perfect optical performance -a good thing since they often don’t know how to collimate their scopes. With this in mind consider the present telescope and its components; the optical tube, finder, focuser, tripod, and mount.

On average the quality of the optics is acceptable for a telescope in this price range. The secondary mirror collimation screws are better than average. However, no special design features have been included for beginners, e.g., knurled thumb screws instead of allen head screws. In contrast the primary mirror collimation screws are nicely done and easy to use. The focuser is a bit stiff but is otherwise acceptable. The secondary mirror support is rather flimsy and can be easily moved around during collimation. Any misalignment in the position of the secondary mirror, for example bending the support arm by pressing too hard on the mirror’s lock screw, will be difficult to correct. The optical tube is very easily dented (this example had many). In general the optical tube is very delicate.

Many companies tend to put poor quality finders scopes on their products and this one is not an exception. A simple unity (straight through) finder would likely be more use.

The wooden tripod legs are simple to use and work well. The only problem is that the spreader bar is held in place with wingnuts and is difficult to install. Three screws need to be removed in order to transport the scope, otherwise various components tend to bend.

The EQ2 mount is by far the limiting component of this instrument: the relatively light weight optical tube completely overwhelms this mount. After a careful clean and adjustment, the mount still had a wobble close to one degree and is frustrating to use. The wobble is inherent in the design and cannot be easily corrected. In addition, the design has resulted in some of the components wearing rather quickly.

In conclusion this telescope is marketed towards beginners and comprises an acceptable, although delicate, optical tube assembly coupled to a mount of questionable quality.

Celestron Firstscope 114 Review Follow-Up 2003-10-11


After posting this review I received a few emails claiming that this telescope must have been abused. Given the unknown history of this particular telescope, we can never know if it was abused or merely well used. However, this summer I made use of an opportunity to visit three telescope stores: one in Montreal and two in Toronto. On display were many entry-level telescopes. Although these were branded by various different manufacturers they all used the same (EQ-2) mount reviewed here. This allowed a comparison of a number of brand-new EQ-2 mounts to one well-used one.

In general the design of all the EQ-2 mounts appeared to be identical. In addition, the mounts seemed to have been manufactured with similar machining tolerances. The new mounts contained the same thick and sticky grease present in the reviewed example.

As for purchasing advice: if you are considering a telescope that uses this mount design then it is recommended that you read this review very carefully and then inspect one in the showroom. Take your time moving the scope through all its axes of motion paying attention to how much play there is. Don’t be fooled by sticky grease: the play is still there - it just slows down the wobbles. Most importantly, try a high-end mount so you see how solid and play-free a mount should be.

On a personal note, the telescope reviewed here has caused a certain amount of unease. It is of no use to me, but I can not sell it to an unsuspecting buyer knowing that the mount is all but useless. In the end I may have to sell it as an optical tube assembly; throwing the mount in the garbage, and taking a financial loss. At least I didn’t pay the new price for it.

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