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  1. #1
    Tom Wales's Avatar
    Tom Wales Guest

    Default OIII filter question



    I recently purchased a Teleview 1.25" OIII filter, tonight was the first
    chance I have had to use it and the only target I could find from the highly
    light polluted skies of my apartment complex was the ring nebula. Using the
    filter made it stand out much better than without. I decided to look for the
    Veil nebula and while sweeping the area where it should have been I noticed
    that while most stars in the FOV looked white there were a few that showed
    up green. Some would blink from green to white and back to green. I never
    did find the Veil which I attribute to the light pollution. Anyway the
    question is; why do some stars look green through the OIII filter and others
    white? And why do some seem to blink between white and green?

    Thanks and Clear Skies
    Tom Wales



  2. #2
    Nicola Montecchiari's Avatar
    Nicola Montecchiari Guest

    Default OIII filter question

    Tom Wales wrote:

    That filtre is made to be used also in light polluted skies so you should see it.


    A complete answer would require a university degree course in Optics. Briefly: the filtre is made with multiple interference layers that should be used at the centre of the field of view. As soon as you move the stars progressively far from the centre of the field of view, the different interference layers of the OIII do interfere in a non optimal way, and that is the result you see.

    Nicola
    http://astrofoto.laza.it

  3. #3
    justbeats's Avatar
    justbeats Guest

    Default OIII filter question

    "Tom Wales" <bbjazzman@nospam.verizon.net> wrote in message news:<3fq8d.10000$na.9122@trnddc04>...

    The color receptors in your eye are most sensitive in the green part
    of the spectrum. Under low light conditions, the color receptors stop
    working and you only get black and white vision. If a star were dim
    enough to be on the edge of colour perception, your eye will be
    flipping between using the rods and the cones which you would see as
    blinking between colour (green) and b&w (white).

    I suspect it was the brighter stars that appeared green and the dimmer
    ones white. The ones in between blinked...

    I'm sure I'll be corrected if I'm wrong :-)

    Cheers
    Beats

  4. #4
    Tom Wales's Avatar
    Tom Wales Guest

    Default OIII filter question

    Nicola and Beats, thanks for the answer. What you said makes a lot of sense,
    thinking back on it the green looking stars were the brighter ones and they
    were only green when they were out of the center of the FOV.

    Clear Skies,
    Tom



  5. #5
    Canopus's Avatar
    Canopus Guest

    Default OIII filter question

    "Tom Wales" <bbjazzman@nospam.verizon.net> wrote in message news:<3fq8d.10000$na.9122@trnddc04>...

    The OIII filter has passband in the green portion of the visible spectrum. See -

    http://www.lumicon.com/filterspec.htm

    - Canopus

 

 

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