Jump to content

  •  

* * * * *

Review of a discarded 2003 National Geographic Society 50mm Refractor


Discuss this article in our forums

Review of a discarded 2003 National Geographic Society 50mm Refractor

MSRP (2023 Model): $27.99 from eBay stores with accessories

 

One of the more interesting things for an amateur astronomer to encounter in the wild is an unexpected telescope.  Whether through the exchange of money in a garage sale, thrift store, through gift or trade, or as in the case of my experience with this telescope – finding it after it was discarded by a prior owner, discovery is what we live for. 

 

Section 1: Discovery and Identification

 

For comparison, the “Classic” variant of this telescope does have differences vs. the “Modern Era” version of this telescope.  While the basic quality, design, and likely value remains unchanged, there are differences which are cosmetic in nature and not felt to make a substantial difference between the classic and modern era variants:

 

Classic 2003 National Geo. Telescope

(as advertised, not as found)

Modern Era 2023 National Geo. Telescope

Dew shield: ~60mm

Dew shield: ~100mm

Adhesive focuser knob covers

(missing on the telescope in this review)

Painted plastic focuser knob covers

Found with a 4mm “High Power” eyepiece and a diagonal mirror.

Accompanied by two eyepieces (4mm & 20mm), a diagonal mirror, a 2x Barlow lens, instruction manual, planisphere, and an aluminum, tabletop tripod that can be classified as Alt-Az

 

With no labels, box, or manual to reference, I set about using the claimed 18x to 180x magnification from box images to determine a focal length through back-calculation using the formula FL/EP (Focal Length/Eye Piece) = Magnification.  Somewhat surprisingly given the claims on the box, the math worked out the same in both cases.  With a telescope like this, it is judicious to trust, but verify, rather than take any claims at face value.  This “Classic” National Geo. Telescope (CNGT) appears to be a 50mm F/7.2 (360mm FL) device.

“Low Magnification”

18x = FL/EPlow

FL = 18*EPlow

FL = 18*20 à 360mm

“High Magnification”

180x = Barlow * FL/EPhigh

FL = (180/Barlow) * EPhigh

FL = 90*4 à 360

 

Section 2: Preparation for Use

An interesting statement is found on the box:

“People use telescopes for all sorts of different things – you can use one to explore the craters of the moon and the rings of Saturn.  Scientists use huge contraptions in space, like the Hubble telescope, to view objects normally undetectable by telescopes on Earth.  Even wildlife biologists use telescopes – for observing wildlife, not space objects!”

-      Rear of CNGT box marketing claim

After reading that, I found myself eager to try it out.  As someone who identifies as one of the people who use telescopes referred to on the box, I decided to use this telescope for all sorts of different things, just like the box said was possible.  Since the original tripod, Barlow lens, and low power eyepiece were not included in the discovery of this telescope, I made the following substitutions:

·         There was no way to mount the telescope, so in place of a standard rings/dovetail configuration, a mitered piece of wood was hot glued to the underside of the CNGT optical tube, meeting Losmandy dovetail specs.

·         In place of the tabletop Alt-Az aluminum tripod, a Skywatcher EQ6R-Pro mount was used to hold the mitered wood mounting plate.  Counterweights proved to be too much mass for the scope to balance, so a counterweight was created from three oranges and a counterweight extension bar.

·         An Apple iPhone13 was used to attempt capture through the 4mm eyepiece with varying results.

·         For reference images, a ZWO 30F4 guide scope with ASI290 was used by hot-gluing a spare SVBONY guide scope dovetail onto the dew shield.  Images were captured by ASI software.  No image stacking or post-processing was done, reference images are raw, single frame captures.

·         I wanted to substitute out the eyepiece, but this scope uses 0.965” hardware throughout the visual train and I actually do not have any of that size to substitute.

In its found state, the telescope was basically unusable, so I disassembled, cleaned, and put it back together, hoping for the best.  A photo of a tree before and after illustrates the difference that the cleaning made.  Despite the improvement, hope was initially low.

Before

After

A white circle with a black background

Description automatically generated

A circular object with leaves in the background

Description automatically generated

 

Section 3: Apparatus as Used

With the accessories (including the battery, guide cam, mount, laptop PC for capturing, and oranges) added to test the scope, the system MSRP had increased significantly over the $27.99.  The intent was to rule out any effect that substandard gear might have on the system in order to achieve the cleanest results possible.  Photos were taken of the setup during daytime and nighttime sessions, the equipment was the same, but results were completely different by session.

Daytime observation

Nighttime observation

 

 

Section 4: Results

Upon completion of cleaning and reassembly, I set about attempting to make visibility tests in daylight first, to familiarize myself with a telescope that was initially an intuitive, yet very uncooperative device.

 

CNGT (90x)

ZWO 30F4 Guide scope

Daytime Target 1: Trees

 

Recognizable as trees through the eyepiece.

Daytime Target 2: Clouds

 

Strangely, blue sky looked exactly the same as clouds through the eyepiece.

 

With my daytime imaging done, I made a plan to image at night and waited for the sun to set, hoping that the cloud cover would break up and the nighttime conditions would be the environment where the CNGT could prove itself, or at least let it do whatever it could do to the best of its abilities given the environment that it would be operating in (indicated by the blue star).

A map with a blue and red line

Description automatically generated

 

 

CNGT (90x)

ZWO 30F4 Guide scope

Nighttime Target 1: Moon.

 

Craters, mare, a clear limb, and terminator were all visible.  The iPhone-EP captures do not do justice to the image that was visible in the eyepiece.  Being a 0.965 EP tube, there was no option to move the ASI290 for imaging.

Nighttime Target 2: Jupiter

 

2-3 of the main moons were visible at most times, and the iPhone-EP captures are not representative of what was actually visible.  This was, by far, the biggest surprise of the night.

 

I was very surprised, given how the daytime tests had performed so poorly.  Nighttime viewing was a totally different experience and appeared to be from a totally different hardware setup.

There were three distinct experiences in this telescope. 

1)   Looking through this particular sample of this line of telescopes during the daytime, as found, was the closest thing I have seen to a cataract simulator.  I have new sympathy for people that have sight disorders after using it.  Daylight viewing does not justify picking it up when coming across it for free, but it is impossible to attribute at least some of the flaws to the condition it was in. 

2)   Once cleaned, daylight viewing was vastly improved, but still very bad.

3)   At night, the scope really surprised me.  It was able to reach focus on both the moon and Jupiter, despite a terrible 4mm EP and a very loose, coarse focuser.

 

Section 5: Conclusion/Summary

I would like to revisit the box’s marketing statement:

A box with a picture of the moon

Description automatically generated

 

In thinking about these claims and the wording specifically, it should be noted that they are made about telescopes in general terms, and not the telescope actually contained in the box, or the one I found, assuming it came in the same or a similar box.  So it is, that this telescope must be judged on its own merits, both against the claims made by National Geographic’s marketing team and in general.

·         Can it be used to see the craters of the moon?  Probably not when found in the condition mine started out in.  After cleaning, the telescope clearly resolved craters on the moon. 

·         Can it be used to see the rings of Saturn?  I have my doubts, but it was able to clearly see Jupiter and it’s at least three of the major moons (Jupiter’s location in Dec 2023 was very helpful).  Sky conditions were such that Saturn was not an option.  If a person had significantly better skies than were available for this review, it would be an interesting test.

·         Can you observe wildlife?  Trees are living things, so, yes, it was able to see a tree.  The strength of this scope is not daylight observing and the equatorial mount chosen for this review is a suboptimal way to observe wildlife.  I really can’t comprehend how this telescope was so bad in the daytime and such a pleasant surprise at night.

To buy or not to buy. 

I would like to have found a complete setup in the wild to test further.  The scope, as tested for this review, would be one that I would be willing to give to a person that I did not like, but even then, I like astronomy too much to spite someone away from the hobby.  For free, this telescope was worth picking up and providing a day’s worth of entertainment, but I would rather spend $27.99 on other equipment. 

Conclusion: Do not buy, whether in “Classic” or “Modern Era” trim. 


  • John O'Hara, deepwoods1, Sergio_2014 and 8 others like this


30 Comments

An amusing review! I've tried to fix one of those National Geographic 50mm's too. It's an education. Those cheap scopes tend to be horrible, but they figure some kid will get it and destroy it in a couple of hours. So no big deal.

>What they can do with these is stop them way down with a baffle behind the objective with a much smaller opening so if it says f9 on the box it might actually be f18. That sharpens things up a bit and improves the color.<

(But) The best part is when they finally get some decent optics and it all takes off into a new dimension. These crappy starting scopes are a stage to pass through so you know the good stuff when the glorious images hit your eye and brain.

They are usually already stopped down because of the long drawtube. It clips the light cone, effectively reducing aperture to 40mm or perhaps even 35mm. 
I found this out firsthand with the Svbony SV502 50mm kids telescope. Got one when they had them for $23 on their ebay store. Unlike most of these 50/360 refractors they come with a 1.25 inch visual back. I was surprised at how sharp it was at 20-60x in daytime viewing. 
But the R&P drawtube was 9 inches long! Way, WAY! more than needed for focusing any eyepiece or eyepiece + barlow. So I took it apart and removed almost 4 inches of tube, easy to do with these plastic focusers. 
Put it back together and……….Hey! What’s going on! The stars at the edge of the field all have tails. Is the objective cattywaumpus? Checked that, no, all squared up. Did I tilt the focuser when I put it back? No, that’s ok too. 
Since stars in the center of the field didn’t have tails it finally dawned on me that I was now looking through the full 50mm of aperture. And even though the system operates at f7.2, there is still distortion off axis. This also sheds light on why my friends 50mm f12 appeared to be so sharp at 60x with a 10mm eyepiece. The slower objective has a flatter field due to the longer focal ratio. 
Anyway, it makes me wonder just how many inexpensive refractors also have light cones clipped by their drawtubes. 
 

    • SporadicGazer likes this
Photo
Horologium1959
Apr 30 2024 12:43 PM

I bought a Konus 50mm scope (F/14). Considering the type, the optics weren't bad---but "tripod" and "finderscope" TOTALLY USELESS.  Seriously---this was better HANDHELD. Anyway, I left a .965 40mm Meade eyepiece on it which gives 17x nice for bords out my back window--IF I DO NOT TOUSCH the scope or its "mount".   Which--i all seriousness is a shame because the actual optics do seem better than what one would expect. might make a useful guide scope.

.

Great review, but where are the interferograms? I bet this has a 0.098 Strehl at least.

Photo
timmywampus
May 02 2024 06:11 PM

Great review, but where are the interferograms? I bet this has a 0.098 Strehl at least.

maybe i should start a gofundme for the higher end bench-testing equipment.  i almost wish i kept it because i am soon going to buy an etalon setup that would have permitted me to have tested it in Ha.

Photo
DolandTheGr8
Jun 03 2024 04:36 AM

I can relate to the novelty of finding an unexpected scope that needs work. For me, finding an old scope, particularly of low value is just fun to learn how to tinker on because if I mess it up, usually the experience is well worth it.

    • John R. likes this


Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics