Sky-Watcher Infinity 76 Information (3" Dobson)

Look | Basic Data | Some Photo Attempts | Preliminary Conclusions | Links

On this page, I present some information about the Omegon 76/300 telescope (purchased at the end of February 2017), which is more or less identical to the Sky-Watcher Infinity 76 telescope.

By the way, this telescope is a (poor?) imitation of the famous Astroscan telescope by the Edmund Scientific Corporation, which was manufactured from 1976 to 2013. The "mastermind" behind this special telescope was Norman Sperling, who tried to revive the telescope, now called Bright-Eye, in a Kickstarter campaign in 2016 (see references below).

 

Look

Unpacking and Assembling

Outer box

Outer box opened

Box taken out of the outer box

Box seen from the side...

...and from the other side

Information texts

Ditto

Box opened

Telescope visible

Box emptied

Telescope on cradle

Telescope, 30 x eyepiece and stickers

Eyepiece taken out of its box

Telescope ready!

Telescope and Celestron FirstScope 76

Telescope side view

Ditto, other side

Telescope rear view

Telescope front view

Secondary mirror

Secondary mirror seen in the primary mirror

Secondary mirror mirrored in the primary mirror

Primary mirror and its fixation

Primary mirror and its fixation

View into the telescope

Light protection for the secondary mirror

Look into the eyepiece holder

Ditto

Ditto

30 x erecting eyepiece

Ditto

15 x eyepiece (bought additionally)

Telescope with cover, side view

Telescope with cover, seen from other side

Telescope with cover, front view

"Cradle"

Telescope standing upright

Telescope with "light protection"

Ditto

 

Basic Data for Sky-Watcher Dobson Telescope Infinity 76 (in Comparison)

Telescope
Meade
Sky-Watcher Skymax/Heritage
GSO
10" ETX 90EC 102 Inf. 76 76 100P 114P P130 GSD 680
Optical Design Newton
(Parabolic)
Maksutov-Cassegrain Maksutov-Cassegrain Newton (Parabolic) Newton (Spherical) Newton (Parabolic) Newton
(Parabolic)
Newton (Parabolic) Newton (Parabolic)
Primary Mirror Diameter 254 mm 96 mm (90 mm) 102 mm 76 mm (3") 76 mm (3") 100 mm (4") 114 mm (4.5") 130 mm (5") 200 mm (8")
Focal Length, Focal Ratio 1270 mm
f/5
1250 mm
f/13.8
1300 mm
f/12.7
300 mm
f/3.95
300 mm
f/3.95
400 mm
f/4
500 mm
f/4.38
650 mm
f/5
1200 mm
f/6
Resolving Power (arc secs) 0.45" 1.3" 1.15" 1.53" 1.51" 1.15" 1.01" 0.9" 0.58"
Limiting Visual Stellar Magnitude ca. 14.5 mag 11.7 mag 12.7 mag 11.2 mag 11.2 mag 11.8 mag 12.1 mag 13.3 mag 14.5 mag
Maximum Practical Visual Power ca. 600 x 325 x 204 x ca. 100 x (150 x) ca. 100 x (152 x) 150 x (200 x) 170 x (228 x) ca. 220 x (260 x) ca. 300 x (400 x)
Optical Tube Dimensions (diam. x length) 35 cm x 119 cm 10.4 cm x 27.9 cm 10.4 cm x 27 cm n.a. n.a. 11.5 cm x 37 cm* n.a. Tube collapsed < 37 cm
(14.5") long
23 cm x 115 cm
Net Weight Basis 12.2 kg 3.5 kg (complete) --- n.a. 1.75 kg (complete) 1.3 kg* 1.6 kg 3.1 kg* 11.2 kg
Net Weight Optical Tube 17.2 kg 1.9 kg 1.2 kg*
(2.5*/2.8 kg complete)
3.7 kg
(5.3 kg complete)
3.25 kg*
(< 6.5 kg or 14 lbs. complete)
9.5 kg
(appr. 21 kg complete)

Dark Blue: Telescopes that I still own; italic and dark red: telescopes that I owned; black: for comparison; *) own measurement

 

Preliminary Conclusions

In the following, I summarize some initial experiences with the Omegon / Sky-Watcher Infinity 76 telescope.

Eyepieces

The Sky-Watcher Infinity 76 telescope is being delivered with a 30 x eyepiece. Apparently, two eyepieces were supplied some time ago, the second one was a 15 x eyepiece. Such an eyepiece with its larger field of view makes it much easier to find objects in the sky, because the Infinity 76 does not have a finder. At Astroshop.de, where I bought the Omegon version of the Infinity 76, I still found a reference to a 15 x eyepiece and ordered it as well - unfortunately only after I had ordered the telescope. So I had to pay for shipping a second time...

The big question for me was now: How good are these eyepieces? To answer the question, I compared the eyepieces with other simple eyepieces using a borrowed Celestron FirstScope 76, because, on the Infinity 76, I can only use its own eyepieces. I summarized my results, which should not be taken too seriously, in the following table:

  Sky-Watcher Infinity*** Sky-Watcher Standard (Kepler?) Plössl Revelation Celestron (Huygens/Ramsden?) Sky-Watcher Infinity (Plössl?) Sky-Watcher Standard (Plössl?) Plössl Revelation
Magnification/
Focal Length
Higher Magnification, Narrower Field of View
Lower Magnification, Wider Field of View
30 x 10 mm 12 mm 20 mm 15 x 25 mm 20 mm
Angle of View medium medium large* small medium medium large
Contrast low mediocre fairly high medium medium fairly high high
Brightness mediocre medium high medium medium higher high
Sharpness mediocre medium very good good (at the center) good (at the center) good (at the center) very good
Details** mediocre medium good medium medium fairly good good

*) large = like a Plössl eyepiece (50-52°); medium = like a Kepler eyepiece (about 40°); small = like a Huygens/Ramsden eyepiece (about 30°); in general, the angle of view seems to be smaller for shorter focal lengths than for larger focal length, but I do not know the reason for this
**) observed using the face of a distant clock
***) with erecting lens

In general, I find it difficult to conduct such comparisons between eyepieces. All my assessments are subjective, only relative to the other eyepieces and should be taken with a grain of salt. They are only meant as an aid for a course rating of the quality of the eyepieces. For evaluating the recognition of details in daylight, I used the face of a wall clock, which was located in a house far away. It showed (and in other comparisons as well...) that less magnification itself rather than contrast and perhaps detail sharpness help in the recognition of fine details.

All in all, in this comparison the Infinity eyepieces fare even worse than the eyepieces that Sky-Watcher delivers with its telescopes as standard (and which accumulate at my home...). I only would rate the Celestron eyepieces lower because of their small visual angle, their low contrast, and their low brightness (sharpness at the center is OK, and therefore you can use them at night).

Because the telescope is mainly targeted at children, the 30 x eyepiece is of an erecting type. Many posters on the Internet, however, found this disturbing and made this responsible for the poor performance of the eyepiece. In addition, the eyepiece magnifies quite a lot, making it difficult for children (and adults) to find objects in the sky without having a viewfinder at their disposal. The 15 x eyepiece would be ideal, its quality is better than that of the 30 x eyepiece, but the image is upside down and therefore it is probably not supplied as standard. Thus, both eyepieces behave differently when you are looking for sky objects. This is a great obstacle not only for children, but also for me. Personally, I would prefer both eyepieces to show the image upside down so that they behave the same, because I have become used to this over the years. With the erecting eyepiece I have my problems, though... Therefore, and not only because of this, I altered the eyepiece and removed the reversing prism. Read more below.

Even more important for me is the fact that Sky-Watcher has devised a special focusing mechanism that prevents other 1.25 "eyepieces from being used on the Infinity telescope, although they would actually fit. More on this below...

Focusing

I had already read in an Amazon review that a buyer found the focusing of the telescope unacceptable. When I myself held the telescope in my hands, I could only but confirm his opinion. The eyepieces have a helical cutout that slides in two guides. By turning the eyepiece you focus the telescope. The insert is lined with fleece to make the movement softer. And these are my problems with this solution:

All in all, I can only call this focusing mechanism "useless," and I do not believe that children will have the patience to succeed with it... Aligning with heavenly objects

Aligning to Sky Objects

The Infinity 76 telescope does not have a finder, but is tilted in its "shell" (or cradle...) and thus aligned. This principle has been adopted from the Edmund Scientific Astroscan telescope. Since I had learned this from the Internet, I was aware of what I had to expect. I simply have to get used to it and practice a bit... According to my first experiences with it, I can, however, state that this is feasible for simple objects (moon, planets, Seven Sisters, ...) at 15 x magnification; it is more difficult at 30 x. I also have more issues with the erecting eyepiece than with the normal one when aligning the telescope with sky objects. This is probably due to the force of habit... Therefore, and not only because of this, I altered the eyepiece and removed the reversing prism. Read more below.

Mirrors

I read somewhere that the 3" main mirror is parabolic - in contrast to the Heritage / FirstScope / FunScope 76 - but there is no further information about this in the documentation or on the box...

The primary mirror has a lot of room in the "belly" of the telescope. A 4" mirror as used in the Astroscan telescope would have fit...

The primary mirror is held by plastic clamps and is probably under tension, as the "multiple" Venus crescents that I can see in the eyepieces suggest (my other "cheap" telescopes show the same phenomenon, but not as bad.) Of course, the primary mirror is not adjustable... I do not know whether it can easily misalign itself as can happen with other Newtons (the Astroscan main mirror was very robust in this respect). Anyway, it cannot be adjusted manually...

The secondary mirror should in principle be adjustable, but I have not yet taken a closer look at this...

Case

The red plastic case is attractive, and I think so, for children, too. I regard the telescope more as a penguin than as a rocket... But the housing is translucent and thus reduces the image contrast during daylight observations. I therefore put a towel over it... At night, the ambient light will probably not be that disturbing.

Light leaks at the eyepiece - the cause is still unclear to me...

Reflexes

When looking through the eyepiece I had a few strong and less strong reflexes in the image at times, which disturb and irritate, of course. I have not experienced this with any of my telescopes. When I used this eyepiece on other telescopes, reflexes also appeared. Since, on the other hand, the 15 x eyepiece, which I bought later and therefore could not try out at the beginning, did not show such reflexes, this suggested to me that the 30 x eyepiece was the cause for the reflexes.

"Modding" the 30 x Eyepiece

As a result, I came up with the idea of ​​unscrewing the eyepiece and removing the reversing mechanism to reduce the number of glass surfaces. The image reversal disturbed me anyway. Since the two eyepieces behaved differently in this respect, I again and again made handling errors. I was able to unscrew the eyepiece at the lower end, and immediately a lens, which was at the end of the eyepiece, fell out of it. As I later learned, this is a Barlow lens.

First I tried to use the eyepiece without the Barlow lens and the reversing mechanism, which turned out to be a prism (see photos below). This worked, however, only in principle, because the telescope could not be fully focused at infinity. Besides, I found magnification lower than originally, but was not able to determine exactly how much. At this time I was not aware that the dispersing lens at the end of the eyepiece is a Barlow lens and thus affects magnification. That is, the two eyepieces might even have the same "original" magnification, and only the Barlow lens would produce the difference factor 2 between them (15 x and 30 x). This would be very "economical" for Sky-Watcher ...

Since focusing was not really possible with this solution and nothing else could be changed on the eyepiece, I decided to reinstall the rear lens. But in this case, there something was missing that would hold the rear lens at the end of the eyepiece in a fix position, since I had remove the reverse prism that performed this task. There was an edge inside the eyepiece, which held the reversing prism in position. This might be used as base for a narrow ring of about 2 cm height I thought. But there was no such a ring in my whole household. I found some rings, though, but only with a diameter of 1.25"... Finally, I discovered a flexible ribbon cable in my electronic stuff, which I rolled up and slightly cut in height. So this was transformed into the desired "spacer." Actually, I would have to paint the inside black, to preserve eyepiece contrast, but regarding the low sharpness of the eyepiece I dispensed with it...

Tests at daytime were not convincing as to sharpness, but reflexes seemed to have vanished. Another test of the eyepiece on the moon, also using another telescope, also did not show any reflexes, and the image of the moon was OK. Thus, I will leave it "as is" for the moment...

The following photos show some details of the "conversion" and of the reversing prism that I removed:

30 x eyepiece "in pieces"; bottom left: reversing prism, fixing ring and dispersing lens

Ditto; bottom: the ribbon cable that I used as a spacer

Ditto

"Empty" eyepiece from the back; the small edge stops the "spacer" cable after the "mod"

Ribbon cable used as a spacer, Barlow lens fixed provisionally

Fixing ring screwed on

Ditto, detail view

Erecting prism from above

Erecting prism from below

View of the prism

Ditto

View from the back

Final Words

Unfortunately, the Sky-Watcher Infinity 76 or its Omegon version is, in my opinion, a missed opportunity for making astronomy accessible to children. It feels for me like a garbage product, which in many points imitates a higher quality product, the Edmund Scientific Astroscan, and might have taken its place if the quality were better, because the Astroscan is no longer manufactured. But as it is, it cannot fulfill these expectations in my opinion. Optics (at least, the eyepieces) and focusing mechanism are unfortunately poor and thus, will keep away many children from astronomy instead of attracting them to this wonderful hobby. The focusing mechanism also requires dedicated eyepieces and thus, prevents the use of other and better eyepieces.

 

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made by walodesign on a mac!
17.03.2017