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© Ciel Extrême, 1998
A 760mm dobsonian that can fit into a Peugeot 106 !
© Vincent LE GUERN
to be rolled down


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Super Deep Sky
Vincent LE GUERN
article published inCiel Extrême number 4

For the general amateur and particular deep sky observer, the fact of increasing significantly the diameter of its intrument involves a complete rediscovery of the sky. Objects are becoming brights, brighter ones are showing more details and numerous faint fuzzies are now accessible.

After having started observing with a 60mm refractor, I really discovered the beauty of the deep sky in a 4-inch begginner's scope: the ring planetary M57 and M27 Dumbbell were contrasted, M13 began to resolve et some galaxies were visible. Four years of observing using various 8-inch telescopes allowed some really stunning views: first spiral arms spotted, central stars and colors on planetaries, globular clusters vell resolved and detailed nebulae.

Five years ago, I invested in a 17.5-inch telescope and it was a revolution again: clear spiral structures with HII regions, globulars completely resolved, gazeous nebula filtered and intricately detailed, quasars and galaxy clusters...

I could have stopped my aperture feaver: such an instrument is enough to fill an amateur's life with observations, and the size of the intrument seemed a limit. But in 1991, I had the possibility of viewing through Jean-Michel COMBES' 24-inch telescope, optically far superior to my Coulter mirors (but 6000F, was a gift fot the student I was...). That gave me aperture feaver again.

In the mean time, americans always pionner in this domain started to design and use monstruous 30-inch telescopes and larger...


.

Three years later, planning, making plans, optimizing, etc., the final plans of a 30-inch were established. It should fit in a small car (Citroen AX or Peugeot 106).

On spring 1995 having collected the financial resources, I ordered the mirror to "Nova Optical Systems", in the USA. Nine months later, after having assembled the mount for myself, I received the mirror. Two days after, on January 11th 1996, Super Deep Sky was to receive first light.

Again, every object looks different: with 3 times the collecting power of the 17.5-inch and a perfect optical quality (thanks to Steve DODDS, boss and optical engineer at Nova), my telescope shows without difficulty spiral arms, Bok globules, HII regions et other exotic objects. New challenges arise.

Spiral galaxies face-one are numerous to show structure details like M51 and M101 but also on M83, M99, M100, M61 or NGC 2903, NGC 3184, ... a long list. A lot of anonymous galaxies are appearing her and there, complicating the identification task.
 

Planetary nebulae are, even for the faintest, exquisite-looking by their wealth of details (inside and outside the NGC): who knows Abell 21 in Gemini. M27 is as complicated as the Orion Nebula in the 17.5-inch. And one has to clutch to the ladder in front of the Veil Nebulae, Omega Nebula or even NGC 6888 in Cygnus.

Golbular cluster are fabulous: the farther ones are partially resolved, the bigger ones are showing thousands of suns.

The former 17.5-inch challenges are becoming formalities; the Corona borealis galaxy cluster, Abell 2065, shows not only two faint ptaches but a dozen fuzzies more, the double quasar in Ursa Major QSO 0957+561 from "very difficul" is now "easy", the M57 central star supports direct vision...

Newcomers are: the pulsar in Crab Nebula M1 and M87's jet of material are visible at 566x with moderate seeing, Abell 1656 the galaxy cluster in Coma is host of about a hundred galaxy to mag16.

The investments in time (100 hours of planning, 200 hours of telescope making) and in money (43.000F overall) are quickly forgotten with the immense pleasure of such observing. The telescope is still user-friendly and one person can point it without difficulty. 15 minutes are nonetheless necessary to get it out of the car and set it up (decharging ramps are helping a lot). The all fits in my Peugeot 106, and no roof carrier is needed.



The dobsonian principle works marvelously. Mécaniquement, le grand principe dobsonien de friction fait une fois encore merveille. In spite of its 108kg (47 for the mirror), the telescope is solid, stable and very easily handled without suffering much from the wind. Seeing permitting, it is not unreasonable to use a 1000x power.

Super Deep Sky shows that a big reflector is not utopic for a motivated amateur. A 20-inch present few problems and could cost less than 20.000F with a correct optical quality.

My mirror is really good according to repeted tests on defocalised stars that show no intra- or extra-focal difference. The miror of a good friend (Obsession 25-inch with mirror from Galaxy Optics) 63.5cm in diameter presented a slight external defect, although the scope performed very well on planets even for avid observers.

I hope to help observers to take the step and conduct a similar project: some free time, an electric drill and a saw are enough ! I am at your disposal for any information needed. A telescope larger than 16-inch is really an inexhaustible source of pleasure.


FICHE TECHNIQUE:
Nom=Super Deep Sky
Propriétaire=Vincent LE GUERN
Monture=altazimutale type Dobson
Tube=ajouré type Serrurier
Diamètre=760mm - Focale=3122mm - F/D=4.1
Qualité optique estimée à lambda sur 10
Poids total=108kg dont 47 pour les miroirs et 61 pour la structure et l'équipement
Hauteur du porte-oculaire au zénith=2,94m (3,22m avec la table équatoriale d'Autume)
Dimensions au sol=925x860mm
Hauteur rangé=700mm
épaisseur du primaire=49,5mm aux bords et 38mm au centre
Barillet=isostatique à 54 points.


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