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Thread: Coma and chromatic aberration ??

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    Question Coma and chromatic aberration ??



    Hello again everyone, I got to thinking about my telescopes,
    I have a Skywatcher SW102 102mm x 510mm (f/5) Achromatic refractor.
    A Saxon 80mm x 600mm (f7.5) refractor.
    A Bintel 200mm x 800mm (f/4) Fast Imaging OTA.

    Now here's my rant !!

    the SW102 is a great little scope, crystal clear, sharp as a tack but suffers from chromatic aberration !!

    The Bintel imaging OTA is fast f4, gathers light really well but suffers from Coma !! can be corrected with a field flattener but reduces it to about f6 and still not guaranteed perfectly flat images !

    The Saxon ED80 is fantastic, takes brilliant images and is my favorite scope but has a fairly narrow FOV.

    I want to purchase a new scope, I am thinking along the lines of a 6" short tube refractor for superior wide FOV...................BUT !!

    I know that if I purchase a 6" non ED glass refractor I'll be paying around $700 - $800 dollars AU and still be haunted by chromatic aberration
    for the same spec in ED glass I will be paying around $3000 - $4000 AU.

    Does anyone out there in Astronomy world no a work around reducing chromatic aberration in non ED refractors or suggest a good alternative ??
    I want to stick with short tube as I don't use a guiding setup !!

    Regards Ivan

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    Skywatcher SW102 Short Tube refractor.
    Bintel. BT200 f/4 Imaging OTA.
    Skywatcher AZ EQ6 GT Mount.

    MAY THE CLEAR SKY"S BE WITH YOU.............ALWAYS !

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    Default Re: Coma and chromatic aberration ??

    Hi Ice,

    I've been looking at the Baader Semi-APO filter as a remedy for my ST80's CA. But I can't seem to get a whole lot of info on this filter as it is pretty new. The product description makes it look like it is exactly what's needed. But we know how straight forward a manufacturers product description is. But Baader is a quality name, so I would sure like to hear if anyone has one and does it work!

    Thanks, clear skies,
    JT
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    Default Re: Coma and chromatic aberration ??

    Hi JT and thanks for the info, I'll do some research on it and see what comes up

    Clear Sky's
    Saxon ED80 Short tube refractor.
    Skywatcher SW102 Short Tube refractor.
    Bintel. BT200 f/4 Imaging OTA.
    Skywatcher AZ EQ6 GT Mount.

    MAY THE CLEAR SKY"S BE WITH YOU.............ALWAYS !

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    Default Re: Coma and chromatic aberration ??

    Hi Guys,
    I just saw this thread, so my response is a bit late! I have the Baader "Fringe Killer" filter, which I understand is basically the same as the "Semi-APO". It does a reasonable job of cutting blue/purple fringing for my Stellarview 70ED (which despite the ED glass is not an "Apo"- and they don't claim it to be). Baader claim it keeps the colour balance, but it does so at the cost of giving the image a yellow-ish tinge. This is not objectionable to me, but it may be to some people.
    With the SV scope the false colour is really only noticeable at high power, and for day-time use you can see fringing of objects with bright backgrounds (like tree branches against the sky). When I use the filter this is cut considerably, but then the sky colour is a greenish blue!
    I haven't tried the filter with a non-ED achromat.
    I guess the bottom line is that filters can help, but can't completely cure problems like this...
    All the best,

    - Dean

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    Default Re: Coma and chromatic aberration ??

    Why not pick up one of the bintel f/4 newts, and a Baader MPCC-III coma corrector - doesn't affect your focal ratio, and removes the coma nicely....

 

 

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