Newtonian reflector tube measurement

[justinshort010]

Hello ist me again had anyone have time to explain or tell me how much extra should I be leaving when I cut my telescope my focal length is 2.46 from my secondary mirror ihow much extra should I provide thanks everyone 

[NGC 1502]

Hi there, it would greatly help if you could give some more information.

It sounds like you’re constructing a Newtonian reflector.  The focal length is the distance from the surface of the primary mirror to the focal plane- that’s where the image is formed and can be examined in the eyepiece. You say the focal length is 2.46. Do you mean 2.46 feet, 750mm?

In a Newtonian reflector the focal length is the total distance from the primary mirror surface, to the surface of the secondary mirror, to the focal plane at the focuser.

Please help us with more details so we can help you. Alternatively you could search for Newtonian telescope construction, there’s a huge amount of info available.

Ed.

[Louis D]

IIRC, rough rule of thumb is to make the tube the same length as the focal length and the tube diameter 2 inches wider than the mirror if using a 2 inch focuser.