| |
You are here: Experts > Science > Space and Astronomy for Kids > Astronomy > 4.5 or 5 inch newtonian reflector
Astronomy - 4.5 or 5 inch newtonian reflector
Expert: Paul Wagner - 10/18/2009
Question
Dear Mr. Wagner;
I am on a limited budget and am considering either a 4.5 or 5 inch newtonian reflector by Celestron. Both of them are under $200 and come with identical equatorial mounts. My question is which would be the better choice. Someone told me that the 5 inch scope in that price range would be heavier than the 4.5 inch scope and therefore be more shaky on the tripod. I do not know whether or not this is true. the 5 inch scope has a focal lenght of 1000mm and is 20 inches long. The 4.5 inch scope, on th other hand, has the secondary mirror supported by a single stalk and I heard that collimating the secondary mirror on these scope is more difficulting than collimating the ones with the four-vane spider like the 5 inch scope has. It has a focal lenght of 900mm and is longer by being about 36 inches.
Any advice/suggestions would be appreciated.
Clear skies.
Randy
Answer
Hi Randy
There is little difference between these scopes---except that the 5 inch wll gather a bit more light. I am a little confused by your comparison, because the 4.5, with a 900mm focal length, is about 36 inches long. The 5 inch, with a 1000mm focal length, must be pretty darn close to 39 inches long. Is there something I am missing? Is the 5 inch a schmidt cassegrain or folder tube reflector? If so, then you are paying a lot of money for that--it would be much more expensive than the 4.5. If you want a bigger and better scope than the 4.5, I would look at a 6 inch Newtonian reflector, which won't be that much more expensive, and will almost double the amount of light you gather.
And while collimation is important in these scopes, it is not hard to do with the single stalk diagonal. The real problem with those is that as you get into bigger scopes, the have to be stronger and heavier...and that impacts a lot of design elements, both physical and optical, for the scope.
Paul Wagner
Add to this Answer Ask a Question
|
|
