Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Spotting scope technique, success wow!!...
    From: Gary LaPook
    Date: 2015 Dec 22, 06:34 +0000
    In the future I will continue to check the IE every time I take observations in order to catch any damage or big change in  the IE. but as long as it stays small i will ignore those IEs and use the one i just found, 0.0.' because those other determinations are not as accurate as this one.

    gl




    From: Gary LaPook <NoReply_LaPook@fer3.com>
    To: garylapook---.net 
    Sent: Monday, December 21, 2015 9:45 PM
    Subject: [NavList] Re: Spotting scope technique, success wow!!...

    That really works. I set up my Tamaya and sighted on a radio tower on a ridge 6.8 NM away. Whenever I took sights I always determined the IE either by using the horizon on the sun's edges method and it was always withing a few tents of a minute of zero. Using the 20 power scope I it turned out to be 0.0'. I then did it over again 20 times, alternating the direction that I approached colimation and it turned out 0.0' each time. The image was sharp and crisp. It really works! 
    Next I put my SNO-T on the tripod and the first thing I noticed was how blurry the image was after being relfected of the two mirrors. I had never realized what poor quality mirrors were on this sextant but the high magnification revealed this problem. the SNO-T is supposed to have a first surface index mirror but mine is a second surface so the mirror must have been replaced at some point. See attached photos.
    gl
    ================================================================================================
    Re: Spotting scope technique, success wow!!...
    From: Mark Coady
    Date: 2015 Dec 21, 19:42 -0800
     I find the sun method on my astra sometimes comes out dead on by happy accident, sometimes misses by .1 - .2 with the 7 power scope.
    I recall a good 20/20 human eye resolves 1 minute. Correct me if I am wrong, that means a 4 power I believe would give you a quarter of that....  .25'  and a 7 power 1/7 of that....  .14'  which is why I embraced a 7 power for lunars very quickly. .......... the other thing is the sextant itself claims a built in seconds of arc resolution limit ....the best claim 9" by manufacture (High end C & P and Tamaya but then tell you you can't read better than 12" in the fine print), while an astra claims I recall 18", because an aluminum arc can't be ground as precisely as brass. That is all a bit esoteric...as to what it really impacts.....but it implies some backlash error built in.  
    Because I started on plastic I got aware of backlash...So when we do the index correction on metal, do I always turn one way, or do I forget the backlash and twiddle both ways.  This has to add a little. Add to this the weather, humidity, filter choice, etc. adn its easy to see how index gets fuzzy sometimes. I find the astra has  one nice feature...color bias filters so the reflected and direct sun can be different shades.  Something that frustrates me with the C & P, which lacks this feature, just because I like it.
    I found the scope method, going only CCW, produced the ability to get zeroed out to practically no discernable error at 20 x.  Back to 7 power, I seemed on distant objects to stay reliably within +/- .1 on test, going one way only on a hard dock with no movement. I kept landing right near zero..sometimes on, sometimes off +/-.   This may be as good as my horrid technique permits. It was damp warm winter air..and thus a slight distant haze. I will try the sun method next chance I get...my guess is I will still miss a little because my eyes aren't super precise and all the other accumulated factors.
    I find the more I do readings, the closer I get to uniform results. Seems I develop unconscious actions which are more precise through repitition.  Beign a perfectionist by nature, I have a tendancy to overshoot to convince myself I was actually right and then back up...which is counter to best accuracy I am convinced.
    For what its worth....read with a skeptical eye and correct me if I missed somewhere......I'd rather be embaressed by my own stupididty than forever wrong. 


    Attached File:

    (20151218_152051.jpg: Open and save)

    Attached File:

    (20151218_152036.jpg: Open and save)

    Attached File:

    (20151218_152021.jpg: Open and save)



       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site