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: Which diameter of the sun in digital photos ?
    From: George Huxtable
    Date: 2009 Aug 21, 15:55 +0100

    A discrepancy of 8% is hard to accept. Something is wrong, as Marcel
    suspects. And such a big discrepancy should be easy to check for.
    
    I suspect the angular calibration of his camera Perhaps he should check that
    more simply, in terms of the angle subtended by an object a few metres away,
    rather than by relying on distant topography. Near enough to that he can
    check dimensions with a tape, yet large enough so that the camera focus
    doesn't need to change from infinity, and also so that uncertainty in the
    position of the effective optical centre of the lens is unimportant (within
    much better than 8%).
    
    Alternatively, even though Marcel considers that the Sun image is not
    overexposed, perhaps it is, and he is looking at a bright halo of light
    around it.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "Marcel Tschudin" 
    To: 
    Sent: Friday, August 21, 2009 12:49 PM
    Subject: [NavList 9583] Which diameter of the sun in digital photos ?
    
    
    |
    | For investigating the refraction near the horizon I perform systematic
    | observations by photographing sunsets. So far I used the horizontal
    | diameter of the sun as a reference scale (pixel per degree) for
    | measuring the sun's position above the apparent horizon.
    |
    | Recently I compared this scale to one derived from pictures of
    | landscapes and found to my surprise that they differ by around 8%; the
    | sun is systematically slightly larger.
    |
    | The scale in landscape photos has been measured with distinct features
    | and the distances measured with Google Earth. The scale for (not
    | overexposed) sun photos has been calculated with the angular size of
    | the sun for the corresponding days; this size is based on the sun's
    | diameter (of the photosphere) and the earth's distance.
    |
    | The difference is not related to refraction since the measurements are
    | made in horizontal direction.  Any idea, why those two scales differ?
    | It is known that some CCDs have a leak in the IR, also the one in my
    | camera. Could this be responsible for it? Does anyone know more on
    | this?
    |
    | Marcel
    |
    | |
    
    
    --~--~---------~--~----~------------~-------~--~----~
    NavList message boards: www.fer3.com/arc
    Or post by email to: NavList@fer3.com
    To unsubscribe, email NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    
    

       
    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