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Review of a DIY 50mm refractor telescope

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Jaegers 50mm Refractor Telescope Review

Refractor telescopes have a long history of being used in astronomy, though that is not at all their first use. The refractor telescope was invented a long time ago, first appearing in the Netherlands in about 1608. Over 400 years ago, can you imagine? So who invented the refractor telescope? According to the Wikipedia Refractor Telescope page, no single inventor has been determined, and thus credit is given to three people of the time, Hans Lippershey, Zacharias Janssen, and Jacob Metius. They worked in making spectacles and instruments in their era, and took their craft to the next level.

The first refractors were simple, a positive curvature lens at the front to create an image, and a negative curvature lens as an eyepiece. For many of the time the small telescopes were kind of a novelty. It was Galileo Galilei who was the first known person to point the telescope into the heavens to see what he could find. Didn't Galileo invent the telescope? No he didn't, but Galileo did make some of his own optics, he just didn't invent the telescope. He invented telescope astronomy.

Galileo's first proclimations about what he saw wasn't received all that well, or even believed. Amazingly, people of the time would look through a telescope at something in the distance and marvel that the device seemed to bring objects closer. Of course, they were familiar with what they were looking at, and had seen such things before at close range. That helped them realize what the telescope seemed to be doing. But when Galileo showed astronomical targets with his telescopes, people tended to simply not believe what they were seeing, as if it were some kind of trick.

Refractor telescopes have come a long way since those early and simple beginnings. Next came two-element objectives that improved images and reduced chromatic (color) distortions. Then came improved eyepieces. Both areas are still being improved. The little 50mm telescope reviewed on this web page is of a pretty modern design, with a long focus two-element cemented objective.

A Gift From A Friend

In the late 1970's, a friend of mine was happily engaged building small refractors in the 2 inch to 4 inch size. He made these using lenses and parts parts he obtained from Jaegers optics, a favorite source of ATMs (Amateur Telescope Makers) in that era. Sadly, Jaegers is no longer in business. As with most telescopes constructed using Jaegers optics, my friend's DIY telescopes were all of excellent quality, many having government surplus lenses.

We often observed together with our respective instruments, and I was always impressed with the excellent views presented by his homemade refractors. One day he made me a gift of one of his DIY telescope projects, a 50mm (2 inch) refractor. I still have it these many decades later, and still use it for some observing. Here you see the telescope, much as it was when he gave it to me. It already had a very nice long-travel focuser for 1.25 inch eyepieces.

The focuser is definitely a plus on this telescope. Most commercial telescopes in this size range use smaller focusers designed to use the 0.965 inch diameter eyepieces. The smaller diameter eyepieces that come with commercial telescopes are commonly of a simpler design with narrow fields of view. Additionally, if you decide to add more eyepieces to your collection, you'll have a difficult time finding quality 0.965 inch eyepieces. Fortunate for me that my friend built the 50mm telescope with a 1.25 inch focuser.

Over the years, all I've done is repaint it and add a finder. The telescope mounts on my DIY Pipe Fitting Tripod. The pipe fitting tripod provides an ultra stable and easy to use mount for the telescope.

I'm happy to report that this fine little instrument still gets regular use, even though I have a number of larger telescopes in my arsenal. Since Jaegers is no longer in business, contructing a 50mm of the quality of my Jaegers telescope would take some time just finding the materials. But I noticed that a comperable 50mm, the Vixen Space Eye 50mm Telescope 32751 is still available. If you compare this telescope to the common discount store variety, you'll quickly see the difference in quality. Direct your attention specifically at the telescope mount.

If you observe regularly with any size of type of telescope, consider filling out the Amateur Astronomer Survey. Then compare your instrument collection and favorite target list with that of other amateur astronomers.

The Details

As you can see in the previous image, the little refractor telescope is rather long looking. That's because it's a classic f/15 instrument -- a full 30 inches (750 mm) long. It's similar in design and dimension to a homemade telescope I constructed myself, which you can see at the DIY 60mm Refractor Telescope page. Check out that page to see how relatively trivial it is to make a quality 50mm to even 70mm refractor telescope of your own.

As such, the telescope has virtually no color distortion, and presents very flat star fields and full field of view moon images. The telescope is constructed using an aluminum tube (I painted it gold to look like brass), and is solid construction throughout.

The objective in this telescope is a coated, cemented doublet. Some 30 years later there is no sign of the cement deteriorating. The lens was delivered already mounted in a crinkle finish lens cell, which made it easy for my friend to mount it to the aluminum tube. Buying an objective lens already mounted in its own cell will make your task much easier if you take on your own DIY telescope project. My friend's advice was to make sure the ends of the telescope tube, when cut down to proper length, are cut and filed to be perfectly square. If you do that, you'll likely not experience any alignment problems after you mount the lens and focuser.


Lunar Apennines Through 50mm Telescope

The performance of this little gem is quite surprising. The image above is a photograph of the Lunar Apennines taken years ago through this fine instrument. The photo was taken using Barlow projection with an EXA 35mm SLR. Given that this image is a snapshot, not a stack of some dozens of images, it falls a bit short of what can actually be seen through the telescope.

For this photo, I used a slow film called Panatomic X. This film was a very high resolution, high contrast film used for photographing documents. Since I needed all the resolution I could muster with this small aperture, I chose it for the photos through my 50mm telescope. I still have the trusty EXA, but if I were to do solar system astronomy with this telescope again, I'd likely use my Celestron NexImage web cam conversion, which I believe has been superseded by the Orion 52175 StarShoot Solar System Color Imaging Camera IV (Black).

You can see more photos taken through this small telescope at the 2 Inch page. Since I have a mylar solar screen for the telescope, I've also used it to get a few images of the sun, as you'll seen on the 2 Inch page.

While my photos through the telescope have been of the moon and sun, the instrument is quite capable of showing many other targets very well. It gives wonderful performance on double stars, clearly showing the favorite Castor (in Gemini) as two bright yellow orbs just short of touching.

Star images through this small telescope give virtually perfect, textbook star patterns. This is due to its excellent optics, and the fact that at 2 inches, it is less impacted by atmospheric turbulence that affects larger telescopes.

Open clusters of stars are also fine objects for this telescope, the Pleiades and double cluster in Perseus being a couple of my favorites. In fact, most of the Messier list of objects can be seen with this telescope if it's used in dark skies, though admittedly the galaxies and planetary nebula, if seen, are usually just visible smudges. In all, there are a few hundred star, nebula, and galaxy targets within reach of this size telescope.

Planets, especially Jupiter and Saturn, make great objects in a telescope this small. At least a couple of cloud bands can be seen on Jupiter, and of course the Galilean moons are visible. The rings of Saturn can be clearly seen, though the Cassini division seems just beyond reach.

And believe it or not, some details on Mars can be seen with this small telescope. I remember seeing some of the larger features on Mars some years ago, when Mars was only about 17 arc-seconds in apparent size. On better oppositions, Mars can appear as large as 25 arc-seconds, so there is potential for seeing even more.

With my mylar solar filter firmly attached (never view the sun through a telescope without a proper filter), I've witnessed two fine Mercury transits of the Sun. Mercury was visible clearly as a perfectly round black dot traversing the surface of the Sun. I remember showing my son that beautiful image, and commenting that it gave some sense as to the incredible size of the Sun. I told him that Mercury is about the same size as our moon, yet is just a dot next to the disc of the sun.

So Why A Review Of A 50mm Telescope?

Mainly to dispel the myth that to enjoy astronomy you must have a large or expensive telescope. What you must have is a quality telescope on a solid mount. Certainly size will deliver brighter star images, most notable on galaxies and dim nebula. And on nights of good seeing, larger telescopes show more planetary detail. But larger telescopes cost much more, are more clumsy to set up, and take much longer to cool off to optimal operating temperature.

I have larger telescopes, but still enjoy using this small instrument. It sits ready to perform, mounted to the tripod. The entire apparatus can easily be moved to my observation area and be ready to perform in minutes. The simple altazimuth mount makes pointing to objects easy and effortless. A perfect instrument for nights where a few quick observations is all I have time for.

And for double star observing, this is one of my instruments of choice. I can of course split even closer doubles with my larger instruments, but seldom do they offer up nearly perfect, textbook star images. The perfection of star images a small, quality refractor can deliver is a joy in and of itself.