NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar distance measurement in ideal conditions: attainable accuracy.
From: Alexandre Eremenko
Date: 2013 Jan 18, 19:01 -0500
From: Alexandre Eremenko
Date: 2013 Jan 18, 19:01 -0500
Greg, Thanks I will try it. What is is supposed to do ? center your eye against the eyepiece? What is the size of the central hole? Alex. > Alex, > > See attached images of scope ocular peep. I used a hole punch through a > piece of thin plastic which was cut to fit in front of the ocular lens. > File folder material will work for trials. Tape in place for experiment. > If it works then make a better one. The peep worked for me on lunars. For > conventional observations the peep is removed. > > Greg Rudzinski > > > [NavList] Re: [NavList 21998] Re: Lunar distance measurement in ideal > conditions: attainable accuracy. > From: Alexandre Eremenko > Date: 18 Jan 2013 18:17 > Greg, > I think I checked all this many times, as well as I could. > And I know that my vision deteriorates with age, and I do not > see stars very clearly without a telescope. > But vision deterioration would give larger dispection, scattering, > not the systematic, constant bias that I observe. > > Conserinng the sextant itself it was checked by Freiberger, > and never traveled much since. > I never noticed any changes in the perpendicularity or index correction. > The bias existed before and after Freiberger's check. > I did not tell this to Freiberger > people because the sextant was almost new then, I had little experience, > and not so much statistics as I have now. > > Freiberger people did not adjust it, except putting some grease > in the night scope eyepiece, because it was slightly shaking. > And they issued a certificate with a table of corrections > in seconds (!), for every 10 degrees, > and the largest correction in this table is 7" :-) > I could never detect any correlation between this table of correction > and observations, and I never use these corrections. > > I agree that the error is small, and can > be easily dealt with because it is constant. But still I was looking for > explanation > and could not find it. > > Alex. > > >> Alex, >> >> 0.3' is a very small remaining systematic error. Declaring this personal >> error may be the best way to go here but before you do that check: >> >> 1. Index mirror perpendicularity >> 2. Side error >> 3. Scope is parallel to frame >> 4. Scope centered on horizon mirror >> 5. Lenses clean >> 6. Focus on Moon craters to get best sharpness >> 7. Lenses free of condensation >> 8. Eye centered in ocular >> 9. Star or Planet split by Moon's limb (not tangent) >> 10. Sufficient shading in place >> >> What I found that caused an unexplained systematic error was not looking >> directly through the center of the ocular lens and then directly through >> the center of the objective lens. Looking from one side of the ocular >> lens >> to the far side of the objective lens caused a noticeable shift of the >> image. A solution for this is to make an ocular peep sight then hold >> your >> eye back off of the peep a bit. This forces centering. >> >> >> Greg Rudzinski >> > > > > ---------------------------------------------------------------- > 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/img/122002.f1-img_1605.jpg > > Attached File: http://fer3.com/arc/img/122002.f1-img_1609.jpg > > > : http://fer3.com/arc/m2.aspx?i=122002 > > >