NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Inverting telescope for sextant
From: Alexandre Eremenko
Date: 2013 Dec 20, 14:13 -0500
From: Alexandre Eremenko
Date: 2013 Dec 20, 14:13 -0500
Noell, Your computation looks correct to me, but take into account that your telescope will probably have lower quality than a factory made one. They usually use the eyepiece consisting of several lenses, to remove the chromatic aberration. One-lens eyepiece will probably have somewhat lower quality of the image. Alex. > The "outside in the sun" folks were correct. the focal length of the > objective lens is 150 mm and Yes, I wear glasses. After thinking all of > this through, I sketched out and attached where I think I am. > 3 X erect scope. > 150 mm focal length of the objective lens. > 110 length of the main body of the scope. > The eyepiece lens should have a focal length of about -50 mm. > The lenses should be arranged with the 150 - 50 or about 100 mm apart. > At the 100 mm mark, the rays from the objective lens will be about 6 mm > across. > The eyepiece holder/sliding tube has a 7 mm aperture towards the objective > lens. > The best choices from Surplus Shed seems to be a DCV (Double Concave) lens > of 10.9 mm x -52 or a 6.77 x -49. There are ACH (Achromatic) lenses > available of 9.5 x -49 and 7.0 x -45. The ACH 9.5 x -49 seems like the > best choice. For $4 to $7 each, I'll probably get an assortment. > > Comments are welcome. > Regards, Noell > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- > > Attached File: http://fer3.com/arc/imgx/Lens-choices-for-3X-erect-sc.pdf > > > : http://fer3.com/arc/m2.aspx?i=125861 > > > >