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  1. #1
    Patrick Candace's Avatar
    Patrick Candace Guest

    Default best way to increase focal length of new webcam to match old?



    My old webcam used the ICX098 CCD. The new one uses a ICX424. According to
    my calculations, I must boost the focal length of my system by about 30% to
    equal the focal length of the 098. What is the best way to do this?
    Someone told me an extension tube would do the trick, but of what length and
    where would it be installed- between the new camera and barlow, ahead of the
    barlow, etc?

    Thanks,
    Patrick



  2. #2
    Martin Brown's Avatar
    Martin Brown Guest

    Default best way to increase focal length of new webcam to match old?

    Patrick Candace wrote:


    Between the barlow and the camera chip to increase magnification.

    Regards,
    Martin Brown

  3. #3
    Roger Hamlett's Avatar
    Roger Hamlett Guest

    Default best way to increase focal length of new webcam to match old?


    "Patrick Candace" <90210@pyr.bet> wrote in message
    newsGcxe.15599$eM6.12883@newsread3.news.atl.earthlink. net...
    You are talking about image scale with regards to the chips, not focal
    length. You don't 'change the focal length of a webcam'. You change the
    effective focal length of the scope, to give approximately the same image
    scale.
    Now a 30% increase is less than most focal magnifiers will provide.
    However it then sounds as if you already have a Barlow in use?. If so,
    then an extension tube will work. You want to increase the distance
    between the chip, and the lens of the Barlow. The amount will depend on
    the focal length of your Barlow. For example, most 'typical' Barlow
    lenses, give about 2*, with the eyepiece directly in the Barlow, and more
    like *3, with the Barlow put in front of a diagonal, then the lens into
    the diagonal (here the diagonal is acting like the extension tube,
    lengthening the light path between the lens and the eyepiece.
    If you look at your Barlow, you will see that it has a lens assembly, and
    above it a tube. The eyepiece will normally have it's focal plane close to
    the top of this tube, and your CCD, probably has it's focal plane just a
    few mm above this point (meaning that the Barlow will actually give a
    little more than 2*). If you increase this length by 30%, then the Barlow
    should give the required extra magnification. In most cases, I'd guess
    that a 1" to 2" extension tube, would give the sort of increase you are
    after.

    Best Wishes



 

 

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