John Dobson (1915-2014), is Astronomical known worldwide for his work “missionary” against the dissemination of astronomical observation of the sky, taken as an irresistible urge to spread (in the "working classes") the construction of the existing simple telescope, all wood and cardboard, that being one of his magnificent project, that bears the name of DOBSONIAN TELESCOPE
The tutorial here indicated in the movie consists of 1992 lasting 84 minutes, It succeeded a oldest VHS, which I took the liberty of adding an Italian audio track with the narrative voice of a hostess “in speech synthesis ", that translates, and in some cases it sums up the meaning of the explanations “to arm” The John.
the purpose, for a similar important document, is the vision of making profit by Italians interested, who remain excluded from important knowledge because of our language “niche”, that by the end of the Roman Empire it is spoken only by us“4 cats”, belonging to the trifle of a centoquarantesimo the world's population.
John knew very well the optics and its rigorous scientific rules, and also the tolerances of a few nanometers necessary for the realization of a mirror objective in Newton “perfect mirror”.
But his genius and are successful in having studied and introduced intelligent building techniques and bare-bones simplicity, in order to achieve the scientific scope and dissemination of building a telescope not perfect but good at least for the visual observation, without having to write a single formula, and always talking so simple, and I would say "agricultural"(*), with solutions that do sometimes make "a leap in the chair" to those accustomed to other types of technologies, or optical tests, or precautionary fears.
It is simple but incisive example:
- When (causes you to jump on the chair because) it drive two nails on the bench using the crude primary mirror as a hammer.
- When he is describing the magnitude of the optical quality tolerances without citing microns or nanometers, but simply saying that they are expressed by a number equal to "About a thousandth (of thickness) of the “Saran Wrap”… (…that are out of my mind to understand what could be the Saran Wrap, to find out later that it is the American polyethylene film, equivalent to the Italian "Domopac" ).
- When it is indicating an amount of abrasive to be used in carborundum grit 60 in each rough grinding wet, approximately "4 times the salt to the scrambled eggs"
- When the indicates the arrow depth of excavation on the concave side of the mirror how about equal to the thickness of a "nickel ", that is, a one cent coin dollar.
- When using hot water to spread the abrasive polishing …( and this is a show of ingenuity and intelligence that's also interesting the most technological Grattavetro (alias glass scratchers))… used in the correction phase of the mirror to "raise" the glass for local heat expansion, reducing the risk of incurring the flaw # 1 fearsome and injurious "Turned Down Edge" on the mirror, for the considerable loss that it generates in the contrast of the image by dispersing part of the captured light.
- When not using either the Ronchi test nor Foucault, and performs optical test "by eye", in oblique vision, or by only using the star test with "artificial star" provided by reflection of the sun onto an insulator of a high-voltage line.
Today “Evolution of the species” and the simplification of portability have also plagued the construction of telescopes Dobsonian “first way”, that it has passed since the original form tube-John, to form lattice type Obsession, and the latest ultra-light form. All, however, with a little technological solutions’ more sophisticated.
But the simplicity of the original project John has remained synonymous with “synthesis”; and the synthesis is “beauty” of thought.
And this beauty is encountered in all solutions that combine simplicity with efficiency. So in all those expressions that enclose the maximum meaning in a few simple strokes.
In this respect is very beautiful a chemical or physical formulas…Or a poem by Eugenio Montale. Why are both sealed in a few letters contain huge concepts.
And the beauty of John's design concept was to show that even something seemingly hard "you can do…in a simple way "; and that one thing from the rough appearance actually works fine.
But stop to the prittle-prattle: The vision of this tutorial takes advantage to all concerned because:
- A Grattavetro "novice" (without neglecting the handling problems of the big telescope) can understand that it might to build as well do it alone, a big telescope diameter: 400 mm F6, scratching a glass 400mm diameter and 25mm often buying the glass of a porthole from demolition of a vessel;
- While a more technological Grattavetro, that have been down that road a few times, You can definitely learn how to profitably use hot water. But it can also realize that there is a parallel possibility of reaching a positive goal, even if only for visual use, while working in such a way much less technical, without using demanding applications that guide you in your work to reach a very challenging maximum, but that with the simple method of John, even if the optical measurement is rudimentary, it is possible that the final quality is not really distinguishable degradation by a beginner naked eye, providing stunning still images perhaps up to 500 magnifications. Allowing air turbulence.
I will list here the minutes in which the film meets the various chapters:
- Title chapter within the movie—————————–Start time
- ROUGH GRINDING – 5’30”
- GRINDING FINE – 19’38”
- CASTING THE PITCH ON TOOLS – 22’59”
- POLISHING – 33’12”
- PURCHASE OF THE TELESCOPE TUBE AND FRAME CONSTRUCTION – 43’44”
- CONSTRUCTION OF TAIL GATE “TAIL GATE” (That is, the CELL MIRROR) – 51’47”
- Eyepiece CRUISE AND SUPPORT SECONDARY MIRROR 1h 04'49”
- STAR TEST for the correction of optical curve – 1h 19’50”
- FIGURING AND CURVE CORRECTION – 1h 21’15”
- METALLIZING MIRROR – 1h 23’13”
- STAR PARTY FINALE – 1h 25’51”
- FINE 1h 28’07”
“TELESCOPE BUILDING” The John Dobson. duration 84′ – NARRATOR VOICE WITH ITALIAN
(*) Refine “agricultural measurements” for example those of a farmer become machinist mill, he described to me the flaws etched on the laminate without the metric system, indicated as great spots like a "grain of wheat", and if more, "Corn"; or large oval bruises as a "wasp" or "hornet", or even a roller mill (due to breakage of the bearings) "She spun like a potato."All universal and intuitive measures known to all…Almost like the metric system.