Focus

[Beldav]

Hello, im new and i am having problems. I recently had a new tube made for my Celestron 114eq. Tube length 1000mm.

Focul length from face of primary to Secondary 855mm.

Have collimated using cap and laser.

My problem is that what ever eye piece i use i cant reach focus. Even using a barlow wont help.

I am trying to focus on mountains in the distance to allign my finder scope.

Please help

[D4N]

I believe this is a bird jones design, do you still have the corrector lens in place?

 

This scope is quoted as being 1000mm focal length (457mm physical length), did you get your figures wrong or are you trying to modify it somehow?

[Cornelius Varley]

4 hours ago, Beldav said:

Hello, im new and i am having problems. I recently had a new tube made for my Celestron 114eq. Tube length 1000mm.

Focul length from face of primary to Secondary 855mm.

Have collimated using cap and laser.

My problem is that what ever eye piece i use i cant reach focus. Even using a barlow wont help.

I am trying to focus on mountains in the distance to allign my finder scope.

Please help

What was the length of the original tube ? And which model telescope ? If the 114 is a Jones-Bird 114/1000 then replacing the short tube with a longer one won't work. The Jones-Bird design incorporates a barlow/corrector lens within the focuser to achieve the focal length and to correct spherical aberrations.  It won't work either if the telescope was originally the 114/500.

[Cornelius Varley]

A longer explanation.

The Celestron 114/1000 reflector telescope which is supplied with either an eq mount (Astromaster 114/1000), SLT mount (Nexstar 114/1000) or LCM mount (LCM 114/1000) is a Jones-Bird reflector. Celestron also sell a long tube 114/900 Newtonian reflector on an eq1 mount (Powerseeker 114/900). The 114/1000 telescope uses a short focal length spherical mirror, probably 500mm, and a barlow type corrector lens within the focuser which gives the telescope an overall focal length of 1000mm and also corrects the primary mirrors spherical aberration. Although the telescope is usually called a Jones-Bird it is more correctly described as a barlowed reflector, a Jones-Bird has a slightly different optical layout. Using the primary mirror in a longer tube won't work because the mirror has a shorter focal length and still needs the barlow/corrector lens placed at the correct distance from the primary for it to achieve focus.