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17th CENTURY and MODERN Single lens refractor

optics refractor lens making classic
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#26 Ovidiu Catalin

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Posted 01 June 2020 - 04:07 AM

One telescope going back to 1660 took up some more time, but the undoubted treasure was an anonymous example. Its main tube features two words: “Tubus Coelestis.”

Over the years, many people have no doubt seen this, and likely assumed it was simply a telescope for doing astronomy. To our great surprise, we determined that it was an example of a style that was widely known, and fully described, but of which there are no other known examples from the 17th century. Or even through the middle of the 18th century. None. And here, in our hands, at last, was one!

Clearly, we had to spend a lot of time making sure of what we had. We documented everything we could, and then did the most fun part: we looked through it.



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  • Singlet refractor 1660.jpg
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#27 Ovidiu Catalin

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Posted 01 June 2020 - 04:25 AM

Tavi F new 17th century telescope replica 38/2060mm homemade lens biconvex simetric, OTA aluminium.


1 https://live.staticf...a74d5284f_o.jpg


2 https://2.bp.blogspo...IMG_6443mod.jpg






5 https://live.staticf...4490d2a55_o.jpg


6  https://live.staticf...32cd08437_o.jpg



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Edited by Ovidiu Catalin, 01 June 2020 - 04:37 AM.

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#28 Ovidiu Catalin

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Posted 02 June 2020 - 09:49 AM

Lens making for telescopes in the 17th century


   Venetian glass makers polished their lenses on a rotating felt or deer skin. It was the only known polishing method at the time and we will discuss it in more detail below. With this method, during the polishing process, the spherical lens initially becomes more and more aspherical, starting first from the edge and then gradually towards the central part. Now the big problem for glass manufacturers was that they had no test method and were therefore unable to control the growing aspherical deformation. Finally, they had many lenses with a huge variation of different qualities. Therefore, Galileo had to examine hundreds of lenses to find some suitable for astronomical use. With the best lenses, the useful central part has a diameter of 20 - 25 mm and, with mediocre lenses, only 10 - 20 mm. All other lenses were good to throw away.

Now, how did Galileo examine his lenses? He had no choice but to put each lens in a tube of the right length and then look at the bright fixed stars on clear nights. Prior to this test, he had to reduce the aperture of the lens to such an extent that the chromatic aberration remained below the resolving power of the human eye. In other words, he had to reduce the aperture of the lens until the different colors surrounding the bright celestial bodies disappeared. This aperture was now the best he could achieve with his unique lenses. Now if the image of the stars had been without bright stripes and rays and the stars were round, the objective glass would have been perfect. However, the more Galileo had to reduce the aperture below this optimal diameter to reduce the remaining defects, the worse it was because the image became darker and lost much of its resolution and detail.
It is now important to realize that Galileo with this test could not get any information about the quality of the lenses on the part covered by the aperture. It was impossible for him to find any difference in quality between a lens with a fine image inside with a free aperture of 25 mm, but with an increasing asphericity to the edge and on the other hand, a lens like "single lens" from Florence which was perfect from the center to the outer edge did not exist. Therefore, our question is: how could Galileo successfully select the lenses, from which it could not determine the quality differences in its test method? From his correspondence, especially with Sagredo, we know that, even in 1618, Galileo had difficulty obtaining adequate lenses for his observations. From the example of a letter from Sagredo, dated April 23, 1616, that, out of a set of 300 lenses, only three were suitable for terrestrial telescopic use and not a single lens for astronomical observations.

   As far as I know, it is impossible to polish spherical lenses to their full diameter using the rotating felt method. Therefore, the belief that the "single lens" belonged to Galileo leads us in particular to the strange assumption that an unknown manufacturer had a secret method, which allows him to polish lenses of the highest quality, which he then mixed with many weak lenses for you kept Galileo busy with a puzzle and that Galileo was in possession of the glass as good as those of the famous Giuseppe Campani 60 years later. We must recognize that the "Galileo telescopes" in Florence remain a mystery and that their age will remain a controversial issue. 


  We can find a description of this early polishing technique in Telescopium Sive Ars Perficiendi Novum. Sirturus described the grinding methods of Venetian lens and mirror manufacturers. However, he found the finishing methods of the lenses very rough and primitive. Grinding molds are formed only by hammer wallpaper without any spherical precision. Sirturus now did his own experiments. He corrected the mold as much as he could with a curved profile and filled the concave mold with molten lead to obtain a convex copy. Now his next action was of the utmost importance. He fixed the concave mold in a lathe and tied the mold to the convex copy of the lead together with grinding material until all the irregularities disappeared. Therefore, we can say that Sirturus was the inventor of the extremely important spherical grinding of molds. It is the only method for obtaining an exactly spherical shape. This improvement in lens manufacturing techniques is a clear step, but it has remained the only one for the next 25 years. Then, Sirturus described how to polish the lens. To do this, he cut a mold into a cylindrical piece of wood and glued a piece of felt or deer skin into it. He then polished the lens on a rotating lathe, using tripolite (diatomaceous mineral) or tin ash. This was also the method of polishing Venetian eyewear manufacturers, and Sirturus did not know how to improve it.
Now everything is clear, with such a primitive polishing method, the perfect spherical shape of the lens after the grinding process would gradually deteriorate from the outside to the inside, as the polishing process continued. The reason was that the felt never kept a spherical shape during the polishing process.
Due to the rotational speed of the felt and therefore the polishing force are at maximum at the edge and at minimum in the center, the spherical shape of the lens would deteriorate the fastest on the outside of the lens, during polishing the asphericity increases more and more to the center.
Towards the middle of the 17th century, it seems that the best telescopes were made by Evangelista Torricelli in Rome and Francisco Fontana in Naples. Despite this reputation, none of them grew in knowledge of the celestial bodies. Therefore, we can conclude that these two artists did not know how to improve the manufacture of telescopic lenses. Now we have found the reason why the telescopes of that period could not be upgraded to a higher resolving power. Rather than the poor condition of the glass, it was a completely inappropriate method of polishing the lenses.


Telescope examined from the beginning of the 17th century


  Manufactured in 1617 or earlier by an unknown manufacturer in Augsburg, Germany, part of the Pommerscher Kunstschrank.
  Main tube and five sections made of cardboard. Each tube is covered with marbled paper; the end tube and the ring stop in the silk velvet with gold thread. The collars, rings and the final tube form a cylinder with a common outer diameter (48 mm), characteristic of other early telescopes.
The box containing this telescope included the documentation of the various artisans involved in the assembly. This documentation makes this instrument the oldest surviving telescope in the world (see Hainhofer's cabinet inventory).
  The lens is flat-convex, full aperture 38.4-41.4 mm. Free aperture between 16.3-17.4 mm. Lens velvet diaphragm: 41.4 (full) and 16.9 (free). When the telescope tubes are extended, the lens separation measures 900 mm.

The focal length of the lens is about 960 mm the eyepiece plano concave with a focal length of 60 mm and a magnification of 16x. Lots of bubbles in the lens. The color of the lens is slightly yellow, while the eyepiece showed a bluish or gray-gray hue.
  The observed field of view is about 4 m at a distance of 1000 m around 15 minutes of arc, for a 6 mm eye pupil opening, but it offers a surprisingly clear, sharp and vertical image.
  The eyepiece lens is plano-concave, full aperture: 22.9-23.8 mm, central aperture: 19.6 mm, thickness 2.2 mm.


Photos here:


1 The telescope



2 Objective and eyepiece



3 Ronchi test of the objective lenss full fdiameter



4 Ronchi test 2 with the center ring indicating the useful diameter.



5 Objective lens



6 Eyepiece lens



7 Objective lens closeup



8 The target statue to be seen through the telescope



9 Image through the telescope at 16x



10 Image through the telescope


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#29 Ovidiu Catalin

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Posted 04 June 2020 - 12:49 PM

Dr Alan Binder Hevelius telescope replica 71mm clear aperture single lens (plano convex) objective and 5.1 meters (206 inches) focal length, homemade telescope.

In recent years, there have been some valiant attempts made by curious individuals to assess the efficacy of these early telescopes. In this capacity, amateur astronomer and planetary scientist Dr. Alan Binder, based at the Lunar Research Institute in Tucson, Arizona, made a systematic investigation of double stars brighter than magnitude 5.5 using an entirely homemade instrument – including the object glass and eyepieces! Calling it the Hevelius, Binder’s telescope consisted of an uncoated, plano-convex objective of 17-foot focus, having a clear aperture of just 2.8 inches. The object glass was placed inside a long wooden tube that was itself mounted on a pole. Three Huygenian eyepieces were employed, yielding powers of 50×, 100× and 150×. Binder investigated its performance on a number of double star targets, acknowledging that only two such systems were discovered during this era using these telescopes Binder showed that about 175 double stars down to magnitude 5.5 could be resolved with this typical 17th century telescope and that it resolved pairs as close

as 2.3 inches, just 50 percent poorer than the Dawes limit (the traditional resolution limit for equally bright components used by double star observers).

The Hevelius was small enough and mounted well enough to allow Binder to accurately point it at many stars in the sky, while those constructed by historical astronomers were often longer and more unwieldy than Binder’s experimental setup. In their zeal to make their telescopes bigger and better, these astronomers of old made their telescopes too cumbersome to use systematically.

It is clear that though the non-achromatic refractor was far from perfection in the modern sense of the word, it was nonetheless used to great effect by a number of astronomers to substantially increase our knowledge of the cosmos


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#30 Ovidiu Catalin

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Posted 04 June 2020 - 12:51 PM


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#31 Ovidiu Catalin

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Posted 14 June 2020 - 02:50 PM

Triel Observatory Aerial telescope - objective is a singlet, 10cm, focal length is 8m and the eyepiece is a Huygens eyepiece The aperture of the eyepiece is about 80mm and was polished by an amateur of the Société Astronomique de France. The objective has one plan-side (tested by interferometric measures) and a convex-side (manufactured and controled with a spherometer)
I love this working aerial telescope replica with wire the same that Huygens used its a little tricky to work with such a telescope and align it with the object and track it but Huygens after using this method for some time abandoned and returned to closed tube telescope, the largest aerial telescope made by him has a aperture of 23cm and a focal length of 210 feet donated to the Royal Society London
The last images are some images taken with a webcam in 2003 - 2004 at Jupiter Saturn and Mars with this aerial telescope.
I think that 10cm aperture of the lens is to big after some tests made 8cm is perfect for such focal length.

Pictures made by Alex Pietrow.


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#32 Ovidiu Catalin

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Posted 09 July 2020 - 09:56 AM

  In the night of June 7, 2020, the sky cleared and the astronomical seeing was good just perfect for observations with the singlet refractors.

First Jupiter and Saturn looked beautiful with long 32/1980mm telescope, the great champion of the observatory who became an even better telescope after some modifications, observations can already be made at weaker objects and now we can start measuring double stars with smaller magnitude, that's why I have made an eyepiece with a very thin reticle with a focal length of 13.3mm, ie 148x through the long telescope, it supports this magnification on the stars, without degrading the disk and the diffraction ring.
Jupiter at 100x was magnificent and with both equatorial bands very clearly visible, and at 116x they could be seen even better and the two polar bands could be seen.
Saturn also at 116x is best seen so far, the rings are very clear, but the surprise was Titan which this time having both tubes mounted looked even better, I looked directly at Saturn with peripheral view and i saw Titan.


Through the 27 / 1250mm simetric telescope the bands on Jupiter are more erased, I could see this for the first time directly at 73x compared to 79x through the 32mm long telescope and it is a well-proportioned detail, I didn't see Titan through the 27 / 1250mm telescope and Saturn is a little darker at 73x with the 27mm telescope than through the 32mm telescope at 79x another aspect that is not related to the focal lenght but the diameter of the objective.

PS. Down below are some simulation images of Saturn and Jupiter there are not real pictures taken with the 32mm singlet refractor but imitations of what i saw at the eypiece.


The moon through the 32/1980mm refractor at 100x.




Attached Thumbnails

  • Simulation Saturn  refractor 32mm  116x.jpg
  • Simulation Jupiter  refractor 32mm  100x.jpg
  • Simulation Jupiter  refractor 32mm  116x.jpg
  • New configuration of the 32mm refractor 2020.jpg
  • New configuration of the 32mm refractor 2020.jpg

Edited by Ovidiu Catalin, 09 July 2020 - 10:34 AM.

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#33 gnowellsct



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Posted 09 July 2020 - 12:59 PM

Wow.  This is fascinating.    I do believe the banding on Jupiter and Martian polar caps eluded Galileo.  But these features were indeed visible in the mid 17th century and probably looked a lot like the images here.  


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#34 Ovidiu Catalin

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Posted 11 July 2020 - 06:15 AM

Last night I went out with a singlet 27 / 1250mm refractor, it was a sensational night where I noticed a lot of deep sky objects in the eyepiece of a good archaic telescope with an exceptional optical quality.
I waited for the night to begin and I left at around 22:30 where I first started to notice brighter deep sky objects and the first object was M13 which could be seen its globular shape with direct view at 39x 32mm eyepiece, and with peripheral vision its appearance came out stronger, as if it had increased in diameter. Then I moved the telescope to Alpha Herculis where I could see the companion attached to the primary star, sometimes visibly with peripheral vision.


Last night there was a great sensation, I wanted to see if I could observe Saturn's moon Titan with the 27 / 1250mm telescope, so I took the phone with the Stellarium application, I rested my sight in the dark to adapt to the dark, then I aimed my telescope at Saturn at 12 o'clock, and focused through the 17mm plossl 73x eyepiece to see if I could see the famous satellite.

Yes, i saw it !! So I didn't think I could see Titan, with peripheral vision I focused on Saturn and a faint star appeared on my lower left, visible only with peripheral vision.

In this method there is a certain degree of estimation, faint stars that easily with your peripheral vision come out "pop out" then stars that are just at the limit to distinguish where you feel like you see something, so Titan was between the two, only with the peripheral vision it could see it, at 62x the same seems a little better than the 17mm eyepiece. Incredible what a powerful tool the human eye can be, in conclusion it all depends on you how good an observer you are, everything is limited to the eyes at the end of the story.


With the 32/1980mm telescope, Titan can be seen directly with the peripheral view without difficulty compared to the 27mm symmetrical telescope.
I went out quickly with a 32mm long telescope to see the planets, I really liked Saturn through the 32mm telescope but I was surprised how well it could be seen through the symmetrical telescope, the image was sharper especially at the edge it produces that perfect focus effect , sharp, knife egde's, the planet looked nice at 73x


The difference between 32 and 28mm or 27mm aperture is relatively small, everything is limited to the eye and the experience of the observer.

Jupiter was a surprise I noticed the cloud bands better this time much more obvious than last time through the 17mm eyepiece, the appearance of the planet is ok, you could notice both bands of clouds easily at 73x, but at 125x already the image has a little fog and pores of the eyes began to be visible, however I noticed the bands.
If astronomers had such optics in the 17th century how happy they were.


Let's see the list of observed objects with the 27/1250 refractor:




M13,M92, M5, M3, M57 , M10 si M12, M17,M27.



Alpha Herculis, 95 Herculis, Mizar, Albiero, Epsilon Lyrae.



Edited by Ovidiu Catalin, 11 July 2020 - 06:19 AM.

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#35 Ovidiu Catalin

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Posted 13 July 2020 - 02:57 PM

Was Christiaan Huygens the best telescope builder?

More than 350 years ago, Christiaan Huygens was proud that his telescopes were the best on earth. He discovered the Saturn moon Titan with it, but Italian scholars followed him with their own telescopes. Research by Museum Boerhaave on the oldest lenses now sheds light on the grinding practices of the earliest telescope builders and on the question of who was best now.

By modern standards, the material with which Dutch astronomer Christiaan Huygens scanned the sky in 1655 was child's play. Maybe even less than that. The performance of the self-built telescope is now surpassed by a children's telescope or binoculars. Yet it was enough to spot a spot of light at Saturn: Huygens discovered Saturn's largest moon: Titan.

Huygens proudly announced that he and his brother Constantijn made the best lenses in the world. Together they drag about thirty lenses, the majority of which are now owned by Museum Boerhaave in Leiden. "Huygens mastered the grinding process very quickly," says Tiemen Cocquyt, curator of the museum, "but whether he really made the best lenses in the world with his brother is still the question. With those statements he probably bumped a few Italian lens sharpeners like Eustachio Divini and Giuseppe Campani. ”

Whether it was the Huygens brothers or their Italian "competitors", in general little is known about the craft of lens grinding at the time - an essential part of the stormy development that science was undergoing at the time. Sharpeners like Huygens left almost no description of their work. The only way to learn anything about the sharpening culture now is to take a closer look at the lenses themselves. From the first half of the seventeenth century, ten to fifteen lenses have been preserved worldwide.


When Cocquyt received a grant from NWO in 2015 to study grinding practices in the seventeenth and eighteenth centuries, he immediately knew that he should not only look at Museum Boerhaave's lens collection. He developed a mobile laser setup with which he visited several European museums and examined some of the oldest known lenses. The work of the seventeenth century sharpeners is thus mapped down to nanometers. As a by-catch, we now know how good the Huygens lenses really were.

Cocquyt had lenses from Dutch and Italian masters in his measuring setup. Compared to Campani's lenses, for example, Huygens' lenses were usually very large. For example, specimens of 4.6 centimeters (Campani) and 9.6 centimeters (Huygens) were compared. "In principle, a large lens is better, but then it must have sufficient quality," says Cocquyt. “Such a format lens is more difficult to get in the right shape due to the larger surface. If something goes wrong during grinding, the entire lens is immediately unusable. There is a delicate balance between size and quality. ”

Were those large lenses from the Huygens brothers really the best in the world? Cocquyt saw that the outer regions of their lenses deviated quite a bit from the ideal shape, especially the aforementioned extra large specimen of 9.6 centimeters. He also suspects that using a diaphragm saved him. “It actually allowed him to take out the" worst "parts of the lens. The center of the lens was in fact good, and the performance of this lens is comparable to that of competitor Campani. So they were about as good, ”said Cocquyt.

For example, from the middle of the seventeenth century the quality of lenses became better and the use of a diaphragm was no longer necessary from that time on. Cocquyt says that Campani's lenses were getting bigger and were of good quality. The lenses were in good shape over the entire surface, in contrast to the decades before. We can only guess at how Campani did that. But Huygens' words that "his telescopes are preferred over those of other scholars" were certainly obsolete at the time. Cocquyt: "Campani eventually became the undisputed grinder among the arguing scientists."



The device is a so-called interferometer. It lets laser light pass through a lens (to be measured) twice and then interfere with itself: the two beams of light fall on a point and stun or amplify each other there. This trick maps the operation of the lens with high precision. “We measure the shape of the lens, which is actually a kind of height map. It is usually precise down to a few nanometers, ”says Cocquyt. "This card says a lot about the grinding quality of a lens."

In the past year, Cocquyt had several lenses in his setup. That of Huygens in Leiden, but also that of Campani from a Swiss private collection. He drove to Berlin for a telescope from 1617 - one of the oldest preserved specimens.

A perfect (convex) lens has the form of a so-called hyperbola. Nowadays, lenses are cut to tens of nanometers of a perfect profile, the seventeenth century grinders did significantly less accurate work. If you look at the height profiles, you will see large deviations from the ideal shape. As a result, the image they enlarged became less sharp. Something that was partly overcome by using a diaphragm, which shields the outer (usually less perfect) regions of a lens.



The first image is the lens with which Christiaan Huygens discovered Saturn's moon Titan in 1655.

The lens itself measures 57 millimeters (just over 2 inches) in diameter with a focal length of 3.6 meters (12 feet) inscribed along the border Admovere Oculis Distantia Sidera Nostris.

On the right, the height profile, the shape, of the lens can be seen as a deviation from the perfect (hyperbolic) lens shape. If the lens had been perfect, the entire area would have been green. However, deviations are visible at the edges (red and blue represent imperfections of approximately 600 nanometers). These deviations arose during the grinding process, for example by pressing harder on the lens during grinding. Ultimately, these deviations result in a lesser quality lens.

Attached Thumbnails

  • Huygens 12 feet objective lens test.jpg
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Edited by Ovidiu Catalin, 13 July 2020 - 02:59 PM.

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#36 Ovidiu Catalin

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Posted 14 July 2020 - 05:48 AM

I return to the DSO through the 27 / 1250mm telescope through a 32mm plossl eyepiece. 

M5. it was easily visible most ok with the peripheral view,
M92. Fabulous globular shape came out well, very ok with the peripheral view I could see the central area brighter than the outside of the cluster having a diffuse appearance.
M57. With peripheral vision it resembles a small defocused star.
M3. Even if it was in the urban halo, I could see the cluster having a round and diffuse appearance, better visible with the peripheral view.
M10 and M12. only with peripheral vision, small circular appearance.
M17. Weak and small visible with peripheral vision, having a linear shape.
M27. Also having a round appearance visible and with direct vision, brighter than m17, with peripheral vision the diffuse aspect comes out more easily, I did not notice the shape of the nebula.




Edited by Ovidiu Catalin, 14 July 2020 - 05:49 AM.

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#37 Ovidiu Catalin

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Posted 14 July 2020 - 06:47 AM

History of the 27/1250mm in images.


Edited by Ovidiu Catalin, 14 July 2020 - 06:49 AM.

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#38 Ovidiu Catalin

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Posted 18 July 2020 - 11:27 AM

  We have introduced a revolutionary new method of observation without an eyepiece but which also has its limits, or not.
People with high myopia are favored for this type of observation, a long focus objective lens is simply mounted on a high support and you simply try to find the focus until the image of the object observed in the lens is formed, only from the focus the place where the rays are converted and where the proper image seen through the objective lens is made, not through the eyepiece.

We have 3 simple lenses at the observatory, one of 2m, 3.5m and 4m focal lengths which is already huge, they are abominable telescopes with small apertures up to 30mm, the most frequent 25mm, the 4m one which is so long that it was only tested on a star at the horizon.
The bigger the myopia, the higher the magnification  it will be, a man who has perfect eyes without problems can get an 10x magnification through a lens with a focal length of 2m, and  20 x at 4m, but people with myopia type -2, -4 and -5 etc they see a magnified image of the object depending on the myopia they have, it's simple the bigger the myopia the more magnification will get, each one will have a different image through such a lens .
This must be verified if it was ever applied in the 17th century, observations through long aerial telescopes without tube and without eyepiece, or  even solar projections at prime focus without the eyepiece to produce the image, in fact the image is produced by the lens in this case, a single lens.


That being said here is the greatest of single objective 4m diopter +0.25 meniscus lens on a tripod. 




I have two objective lessens both of +0.25 dioptrice but I noticed that they have totally different focal lengths one of 3500mm and the other long of 4008mm measured in the Sun also from on board with roulette a more difficult task maybe the one with 4m reaches up to 4.1m, who knows, I didn't have the necessary means to measure it precisely, that is, it is positioned between 4m and 4.1m, the one with 3.5m I know exactly how much it has being measured much easier than the one with 4m length.

At the time of the observation the Moon was up in the sky towards the zenith totally unfavorable position for such focal length as much as I tried to raise it higher to acceptable limits the focus was below actually enters the ground I changed, the lens to 3.5m long one and with that lens i studied the Moon the focus being exactly at the limit where I had a comfortable position.
The surface of the Moon was visible in sections with the naked eye without an eyepiece in hand and with an eyepiece it looked good at a power of 48x 72mm simple eyepiece, I preferred the method without eyepiece, the image was almost like a keyhole to a plossl eyepiece, but seen with my own eyes as if the image of the Moon tended to be like a projection in space very interesting phenomenon, the image having the same diameter or field apparently as the diameter of the objective cell seen from 3.5m, away and the cell is about 8.8 cm in diameter. 


In order for you see what I saw without an eyepiece, I defocused the phone's camera with the mf function and I adjusted the exposure and then I shot some frames to made out exactly what I see with my own eyes through the long 3.5m objective.











This is the setup










The shooting is much better than the pictures taken at maximum zoom, which limits the image quality, otherwise the image of the Moon is much too small.
Here's the filming


In the movie I reduced the brightness too much, the Moon being much brighter through the lens and much clearer seen with my own eyes than in filming, of course I put maximum zoom otherwise it is not visible on the camera.

Edited by Ovidiu Catalin, 18 July 2020 - 12:00 PM.

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#39 Ovidiu Catalin

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Posted 07 August 2020 - 05:41 AM

Go optical goo !!! New observations with the 27/1250mm refractor are amazing, last night i saw many DSO objects and double stars with just 27mm aperture:

M57, M3, M2, M13, M5, M10, M12, M27, M92, M15, M13, al at 39x and 50x.



Eta Cassiopeia, Cor Caroli, Mizar, 12 Del, 95 Hercules, Gamma Delphinus, 70 Ophiuchus, Pi Bootes. Al at 50x magnification.


Greatest discovery in 2014 with de 27/1250mm singlet refractor i was unable to se the companion of 70 Ophiuchus but now in 2020 i was amazed to se at 50x the companion of this double with a hair split, this proves that this refractor is perfect for double stars observation, i never noticed this chance with a 70/900mm SW refractor or with the Mak 102mm, the nice airy discs and diffraction ring made by this long focus single lens are amazing and great as a reference for double stars chance over time. This proves that single lens refractors are perfect for double stars observations.

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#40 Ovidiu Catalin

Ovidiu Catalin

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Posted 12 January 2021 - 11:51 AM

Happy new Year wink.gif bow.gif

 The 28/1250mm refractor and modern zoom eyepiece Sw 8-24mm.

In the last weeks a have made some observations with the singlet refractor on double stars, Gamma Andromedae,  was a beautiful sight with the small companion star touch the primary one at 71x magnification, the scope can go on double stars even at 130x magnification but with the dimming of the field of view and object.

Castor, Sigma Orionis, Meissa.

Mars, was in phase and small at 52x magnification and on 70x was bigger but no details, at the opposition last year i saw the markings on the surface of mars at 50x and 71x with the singlet 28mm refractor, it was amazing to see that with a singlet telescope.

The beautiful image at double stars with large airy disc makes this scope a good tool for these objects, a bigger aperture had been better but the long focal length of these scope makes them very difficult to use. The long 32/1980mm Hevelian scope was dismounted completly and put to rest, because the 28mm refractor objective quality is much better than meniscus objective lens used in the 32/1980mm scope i made the decision to disassemble the scope, also it was difficult to use because the board had some deformations ( it curved) under temperature changes over time this had some effect in the collimation of the scope.

I use now the 28m refractor because its much better.


 Last Year achievements with the 28/1250mm refractor


1 Details on the surface of Mars at opposition.

2 Other DSO objects seen with the scope small aperture. ( M10, M12, M7, M29, etc)

3 Titan the moon of Saturn seen at 39 and 60x magnification at opposition and before opposition.

4 New double stars seen and separated: eta Cass, 70 Oph.

5 Jupiter band easily seen at 50x at opposition.

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#41 Astrojensen


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Posted 12 January 2021 - 12:17 PM

I just received some 50/1000mm singlet lenses, so I'm going to build one myself, soon. Working aperture will likely be 25mm, but it depends on how well the lens performs. 



Clear skies!

Thomas, Denmark

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#42 starcanoe



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Posted 12 January 2021 - 12:48 PM

I just received some 50/1000mm singlet lenses, so I'm going to build one myself, soon. Working aperture will likely be 25mm, but it depends on how well the lens performs. 



Clear skies!

Thomas, Denmark


For future reference...where you get em? 


I really want to build a long singlet....would also really help attract folks passing by at our public outreach events....

#43 Ovidiu Catalin

Ovidiu Catalin

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Posted 13 January 2021 - 11:15 AM

Here is some reference:





#44 Ovidiu Catalin

Ovidiu Catalin

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Posted Today, 08:25 AM

The 32/1980mm Hevelian refractor has been re-made, i just adjusted the main scope with laser collimator and added a new straight board under the main one and i have ajusted the collimation with all the screws that hold the main board until the laser hit the middle of the objective lens.

The board under the main one has been grind straight this made it easy to eliminate deformations when i tighten the nuts, its a easy to collimate once and this can stay for a long time, because the wood works over time the advantage is to use a focal length of least 2000mm when you mount it on a single mount at the balance point, when you surpass 2000mm focal length the best way is to mount the tube on two points, one in front and the other one at the eyepiece, this is to prevent the bending of the OTA in time.




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