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  1. #1
    Roland Herrera's Avatar
    Roland Herrera Guest

    Default Frogs, toads... and chromatic abberation



    Group,

    I'm serious : I have a backyard / patio but the frogs and toads come out
    at night and creep up on me. I hate the things, and would love to get rid of
    them, but I'm frightened to go anywhere near them. They actually cut short
    my observing tonight.... what shall I do ?

    Roland Herrera

    P.S. My OMC140 gave a blue edge and a red opposite edge to Mars tonight...
    this looks like a huge amount to chromatic abberation... ( I took away star
    diagonal to eliminate that particular possibility ) - Is strong chromatic
    abberation normal in Matsukovs ? Mars was a fuzzy blob, mostly... polar cap
    clear and dark marking in that half, but poor detail.



  2. #2
    Michael A. Covington's Avatar
    Michael A. Covington Guest

    Default Frogs, toads... and chromatic abberation

    > I'm serious : I have a backyard / patio but the frogs and toads come
    out
    of

    They won't hurt you. What's to be afraid of?

    star
    cap

    Chromatic aberration in the telescope would be symmetrical, and, no, Maks
    don't have much of it. When a planet is red on one edge and blue on the
    opposite edge, it's because of atmospheric dispersion (chromatic aberration
    in the air, not the telescope). The cure? Make Mars rise higher in the sky



    --
    Clear skies,

    Michael Covington -- www.covingtoninnovations.com
    Author, Astrophotography for the Amateur
    and (new) How to Use a Computerized Telescope




  3. #3
    Robin Leadbeater's Avatar
    Robin Leadbeater Guest

    Default Frogs, toads... and chromatic abberation


    "Roland Herrera" <wps@blueyonder.co.uk> wrote in message
    newsHr9b.64$Vs2.49@news-binary.blueyonder.co.uk...
    out
    of
    star
    cap
    Hi Roland,

    I can put your mind at rest over the Chromatic Aberation. It is caused by
    the atmosphere. It is particularly noticeable on Mars because it is so low.
    Try looking at a star near the horizon, you will see the same effect. now
    look at one overhead and you should see it is gone. Mars is terrible here
    tonight from Cumbria. Poor transparency and seeing and getting worse - a
    fuzzy wobbly blob. This face of mars is not particularly interesting
    either. I have just given up trying to image tonight.

    Sorry I do not have any suggestions to scare the frogs away though!

    Here is hoping for some
    Clear Steady Skies

    Robin
    ----------------------------------------------------------------
    Robin Leadbeater
    N54.75 W3.24
    www.leadbeaterhome.fsnet.co.uk/astro.htm
    ----------------------------------------------------------------



  4. #4
    Michael A. Covington's Avatar
    Michael A. Covington Guest

    Default Frogs, toads... and chromatic abberation

    My daughter suggests that a cat would scare away the frogs.



  5. #5
    ChrisH's Avatar
    ChrisH Guest

    Default Frogs, toads... and chromatic abberation

    On Tue, 16 Sep 2003 00:12:11 +0100, "Roland Herrera"
    <wps@blueyonder.co.uk> wrote:

    I know what you mean, just don't go out observing in your bare feet
    'cause it's a right bastard getting the squishy bits out from between
    your toes. Wear a pair of wellies.


    This is atmospheric dispersion and nothing to do with your telescope.
    What we are cursed with in the UK with Mars being so low in the sky.

    ChrisH

    UK Astro Ads: http://www.UKAstroAds.co.uk

  6. #6
    ChrisH's Avatar
    ChrisH Guest

    Default Frogs, toads... and chromatic abberation

    On Mon, 15 Sep 2003 21:51:45 -0400, "Michael A. Covington"
    <Michael@CovingtonInnovations.com> wrote:


    I have a family of hedgehogs living under the shed, they'll clear a
    garden of frogs in nothing flat. Unfortunately they've got disgusting
    table manners and frogs are quite crunchy.

    ChrisH

    UK Astro Ads: http://www.UKAstroAds.co.uk

  7. #7
    Stephen Tonkin's Avatar
    Stephen Tonkin Guest

    Default Frogs, toads... and chromatic abberation

    Roland Herrera <wps@blueyonder.co.uk> wrote:

    Get a cat.


    Don't worry, it's due to dispersion of light by the atmosphere. You will
    find it with any bright object at low-ish altitude. If you really want
    to see the effect in all its glory, watch a bright star like Sirius rise
    (get up early) -- it appears to flash different colours.

    Best,
    Stephen

    --
    + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
    + Stephen Tonkin | ATM Resources; Astro-Tutorials; Astro Books +
    + (N51.162 E0.995) | <http://www.astunit.com> +
    + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +

  8. #8
    Darren's Avatar
    Darren Guest

    Default Frogs, toads... and chromatic abberation


    "Roland Herrera" <wps@blueyonder.co.uk> wrote in message
    newsHr9b.64$Vs2.49@news-binary.blueyonder.co.uk...
    out
    of

    Don't give up in the face of frogs and toads. By avoiding them and letting
    them rule your actions you're on the way to obtaining a phobia. I have/had a
    phobia of spiders and am now in recovery, the trick is to not get one in the
    first place.

    If you want info on how to beat your fear, mail me (watch out for the
    obvious spam block on my email address) and I'll talk it through with you.
    The basic idea, as horrible as it seems at first, is to face your fear and
    keep calm. It DOES work!

    Good luck,

    Darren



  9. #9
    ChrisH's Avatar
    ChrisH Guest

    Default Frogs, toads... and chromatic abberation

    On Tue, 16 Sep 2003 05:22:31 +0100, Stephen Tonkin
    <nospam@astunit.com> wrote:


    My neighbour's cat just catches frogs deposits them inside their house
    like some sort of trophy. :-)) Does the same with mice and birds - I
    suppose it thinks it's clever.

    ChrisH

    UK Astro Ads: http://www.UKAstroAds.co.uk

  10. #10
    Mike Dworetsky's Avatar
    Mike Dworetsky Guest

    Default Frogs, toads... and chromatic abberation



    "Roland Herrera" <wps@blueyonder.co.uk> wrote in message
    newsHr9b.64$Vs2.49@news-binary.blueyonder.co.uk...
    out
    of
    star
    cap

    This is atmospheric chromatic dispersion, not chromatic aberration (CA).
    Your Mak probably has negligible CA and is an excellent planetary telescope.

    There are ways to cancel atmospheric dispersion, specifically by inserting a
    thin prism in the light path. The prism needs to be the right shape and
    direction (in altazimuth--dispersion is vertical) to do this correctly.

    Atmospheric dispersion is effectively negligible for zenith angles less than
    45 degrees. It is caused by the fact that the atmosphere refracts blue
    light more than red light, raising its altitude above the horizon and
    drawing a star image out into a short spectrum. For a planet, this results
    in one blue limb (top) and an opposite red limb.

    There are such prisms on the market, in the UK they are sold by TTL (Trutek)
    and Edmund Scientific. Usually the angle needed at the apex is between 1
    degree and 8 degrees (for very low objects). There is also a variable
    design called a Risley Prism which is used at professional observatories and
    by some amateurs.

    Ask at

    http://www.trutek-uk.com/ who sell the Astrovid PADC (prismatic atmospheric
    dispersion correctors). You can read about it on the Astrovid web site.

    There was an article about this in Aug Sky and telescope, but they did not
    mention the PADC product specifically.

    --
    Mike Dworetsky

    (Remove "pants" spamblock to send e-mail)



 

 
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