Sunday, February 8, 2015

Constructia reflectorului meu de 125mm F/4.5 / Making of my 125mm F/4.5 RFT reflector

Actualizare / update February 2018 :

Tribute to Clyde Tombaugh , the last great  observer astronomer :

This project of making a 125mm F/4.5 RFT Newtonian reflector was inspired   by  Clyde Tombaugh who described   a similar instrument  in  ''ATM Books'' edited by Albert G. Ingalls.
My telescope is of course a pale copy while the five inch  RFT Newtonian of Clyde Tombaugh was a very pioneering endeavour in the first quarter of XX Century.
Below is a picture from the article ''Young Clyde Tombaugh :How a Midwestern farmboy set a course for Pluto'' by Kevin Schindler of Lowell Observatory , published on ''www.astronomy.com''.
The picture is courtesy Tombaugh family.
It is not specified in the article but I strongly believe that Clyde Tombaugh is seen here holding  the five inch RFT Newtonian described in the ATM Books.
I believe in the same book it is mentioned another five incher , of  very long focal ratio , of  F/15.
The RFT and the long reflector in the picture have tubes of the same ( or very close) diameters , any of them seem not to be a 7 incher as stated in the article.
The short one should be the famous RFT Newtonian described in the ATM Books.





Now coming back to my RFT project :

Am schimbat planul ,am renuntat la portocularul de 2'' deoarece utilizarea ocularului LV 30mm / 2'' cerea o cotire newtoniana  prea mare a fascicolului.
Aceasta cotire exagerata avea drept consecinta reducerea campului de plina lumina la valori de 6-7 mm.
Am revenit la solutia constructiva cu portocular pe standard 1.25''.

I had to change to change my plan to build the RFT reflector with 2'' focuser .
Due to the deep recess of the field stop in the LV 30mm ocular , the bending of the light path would be too big.
This excessive bending would lead to a too small fully illuminated field.
So I went back to the 1.25'' focuser.

Vedere de ansamblu a telescopului RFT tip Newton cu apertura de 125mm F/4.5 :

Overall view of the 125mm F/4.5 Newtonian RFT :





Montura pe care voi folosi telescopul RFT este ''Penelopa'',montura mea ''pipe'' realizata cu fitinguri de 1.5'':

The mounting on which I will use the RFT telescope is my ''Penelopa'' 1.5'' pipe mount :




O vedere laterala :

Side view :



Capatul ocular al reflectorului , se vede portocularul filetat DIY de 1.25'' cu ocularul Plossl ex-militar de 31mm si talpa cautatorului  (cadou de Craciun de la prietenul meu Armand al carui  blog astronomic apare in blogroll-ul meu - cautatorul tip RDF nu apare in poza) :

The business end of the reflector , one may see the helical DIY helical focuser holding the 31 mm ex-military 31mm Plossl ocular and the finder bracket (a Christmas gift from my friend Armand whose astronomical blog is on my blogroll -the finder itself is not visible in the pic ) :



Placa de baza a  barilletului oglinzii principale :

The base plate of  the primary mirror cell :



Pentru inaugurarea reflectorului RFT am spala-curatat ocularul ex-militar de tip Plossl 31mm
Aici vedem lentilele ocularului ,pregatite pentru curatare :

For the ''first light'' of my RFT reflector I had to clean the 31mm Plossl ocular.
Here we see the lenses of the ocular :



Lentila de camp are un diametru mai mare decat al lentilei  de ochi :
The field lens have a wider diameter than the eye lens :






Montura originala ,din alama , compusa din corp , distantier si inel de retentie :
The original brass body of the ocular , consisting of the barrel , spacer and retainer :



Adaptorul ocularului la standardul de 1.25'' , executat ''in regie proprie'' din otel , la un atelier de prelucrari mecanice , consta din corp , inel filetat si diafragma de camp (nu se vede in poza).Brunarea otelului am realizat-o acasa dupa metoda  descrisa aici pe blog  :

The adapter to 1.25'' standard was machined of steel and consist of barrel, retainer and filed stop.The blackening of the steel was made at home as descibed elsewhere on the blog:


Iata ocularul gata curatat ,pregatit pentru ''prima lumina " a telescopului RFT :
The ocular ready for the ''first light'' :



Am reusit sa testez telescopul RFT dar numai pe cerul dominat de Luna Plina.
Constatari : 
-Campul vizual real este in jur de 3 grade la grosismentul de 18x ,obtinut cu ocularul Plossl 31 mm.
Campul vizual aparent al ocularului Plossl 31 mm este cu aproximativ 10% mai mare decat cel al ocularului Sirius Plossl 25mm.
De unde convingerea mea ca obtin cu adevarat un camp vizual efectiv de trei grade pe telescopul RFT.
-Desi am insistat timp indelungat pe colimarea oglinzii secundare ,aceasta nu este inca perfect colimata.Am constatat la lumina zilei ca butucul si bratele paianjenului secundarei sunt excentrice fata de axa optica.
Am rezolvat cu usurinta stele duble si multiple Iota Ori /tripla, Sigma Ori /tripla , Beta Mon / tripla , Zeta Ori , Lambda Ori,Trapezul cu patru stele .
Totusi nu am reusit sa rezolv stele duble cu separatie mai mica de 1.8''.Astfel am fost oprit la stele de dificultatea dublei Eta Ori.

I was able to test the RFT reflector only on the sky strongly lit by the Full Moon.
Findings :
-The real visual field is around 3 degrees at 18x obtained with the 31 mm Plossl ocular.
The apparent field of view of the 31mm Plossl is 10% wider than that of the Sirius 25mm Plossl ,so I;m confident about achieving the targeted 3 degree real field.
-I spent a lot of time colimating the secondary mirror.However there is still work to do ,I found next day the hub and arms of the spider as being eccentric to the optical axis.
The telescope easily split double and multiple stars such Iota Ori /triple ,Sigma Ori /triple , Beta Mon /triple ,Zeta Ori ,Lambda Ori , four stars in Trapezium.
However ,I was not able to split below a separation of 1.8''.
So I was stopped after splitting double stars  like Eta Ori.


............................................................................................................................................................

The previous incarnation...

First,the mirror was cut, polished and parabolised  by amateur astronomer Attila Csillag  of Arad, in a series of three identical mirrors.Parabolisation of the first mirror went very well, is powering since then Attila's  RFT reflector.

                        On  the second mirror the parabola resulted zoned ,the zone  from 0,7R   outward being  in a parabolic surface with a slightly different focal length.
This become my RFT mirror.
Correction of the defect was made by the Hungarian optician Csatlos Geza  who resumed the process from the grinding with the finest abrasive.
In the picture ,one can see the signature of Csatlos Geza ,reflected by the Aluminium coating.
Oglinda a fost debitata ,slefuita si parabolizata intai de catre astronomul amator aradean Csillag Attila ,intr-o serie de trei  oglinzi identice.
Parabolizarea primei oglinzi a decurs foarte bine ,ea echipeaza reflectorul RFT al lui Attila.
La a doua oglinda insa ,parabola a iesit zonata ,zona de la 0,7R spre margine a rezultat intr-o suprafata parabolica cu un focal usor diferit.
Corectarea acestui defect a fost efectuata de catre opticianul Csatlos Geza din Ungaria care a reluat procesul de la slefuirea cu cel mai fin abraziv.
Se vede partial semnatura lui Csatlos Geza pe spatele oglinzii ,reflectata de stratul de aluminiu.









Am montat intai oglinda intr-o montura azimutala in furca cu un singur brat si pe care o avea Attila disponibila.
Initially , I mounted the mirror in an  azimuthal  single fork arm mount that  Attila had available.



Dupa ce a stat in acea montura vreo zece ani ,timp in care a fost rar utilizata ,am considerat ca a venit timpul pentru realizarea unei noi monturi.
After staying in the mount ten years, being rarely used, I thought it was time to make a new mounting for it.

Componente ale tubului optic.
La stanga ,portocularul filetat pe standard de 2 inch si placa adaptoare la raza tubului.
In mijloc,barilletul oglinzii principale.
La dreapta placa de montare a tubului optic pe montura.
Parts of the optical tube.
Left, the   2-inch threaded focuser and his adapter plate to the radius of the tube.
Middle,the cell of the primary mirror.
Right ,the mounting plate of the OTA to the telescope mount
  


Placa -suport a oglinzii principale este gaurita pentru usurarea ventilatiei naturale.
Oglinda va fi lipita la 0,4 R ,unde se vad petele galbene,cu silicon.
Suportii laterali ,din partea ''de jos'' a oglinzii ,sunt la 90 grade ,nu la 120 grade ,dupa cum ne sfatuieste Texereau
( in poza , reazemele laterale  din dreapta si din centru - sus ).
 The primary mirror plate is drilled for easy natural ventilation.
The mirror will be silicone glued at 0.4 R, where are the yellow dots.
Side supports ,( from the 'bottom' of the mirror ) , are spaced at 90 degrees, not at 120 degrees, as advises by Texereau.
(  the side supports at the right and  center - up ,in the picture).
Viitorul tub optic ,cu cateva dintre componentele mecanice.
Under development OTA ,with some of the mechanical parts.

Actualizare.Updating. 3 Mai 2015

Confectionare diafragma portocularului ,dupa recomandarile lui Mel Bartels.
Making the focuser baffle,according to Mel Bartels recommendations.



http://www.bbastrodesigns.com/baffle.html



Grunduire.Primer painting.



Vopsire interna si externa.
More painting.