Quote:
Originally Posted by brian nordstrom
 Here is my 10 inch f10 newt with a 1 inch diagonal , thats her in 2 pieces .
the Dobbo base , next to Goldie , and the top 1/2 , now you want to see Jupiter in this baby !!  .
Go buy an 10 inch f/5 , it will give great views up to about 200x , thats where my 5 inch f/13 is just comming on song ..
Brian . |
Brian the F- Ratio of the telescope has nothing to do with the magnification it is capable of supporting. What determines that are the following parameters:-
1) The thermal stability of the optics
2) The quality of the optics
3) the aperture of the optics
4) The atmospheric conditions (seeing)
Given good thermal conditions and seeing, it's a pretty poor 10" telescope that will not go infinitely higher than 200X on anything. That's only 20X per inch of aperture. A good telescope irrespective of F-ratio should do at least 40X and generally 50X per inch of aperture under favourable conditions, irrespective of F-ratio. In the early days it was a lot easier to make a good F10 mirror than it was to make a good F5 mirror, consequently, some of the faster mirrors were of poor quality and would not hold up under high power, but that changed decades ago. Skilled opticians are now producing < F5 optics which are of outstanding quality and capable of excellent high power planetary performance. The design parameters of the telescope where it has a thin mirror which cools fast and a small < 20% central obstruction are the most important factors and far more important than the F-ratio.
I have two 10"/F5 'ish telescopes. One is a 10"/F5 tubed dobsonian with a GSO mirror (which is very good) and the other is a 10"/F5.3 SDM truss dobsonian with a Mark Suchting mirror. Once the scopes have cooled properly they will both pull 500X plus under favourable conditions, on their ear.
Cheers,
John B