ASA 4" Ritchey-Chretien Field Flattener

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    ASA 4" Ritchey-Chretien Field Flattener

    ASA 4" Ritchey-Chretien Field Flattener

    When using a Ritchey-Chretien telescope system, it should be used with a field-flattening accessory lens to achieve a larger useful field of view over a truly flat image plane. This is because a Ritchey-Chretien scope without a corrector is only marginally better than a classical 2-mirror Cassegrain scope. ASA provides this corrector lens, the 4" Ritchey-Chretien Field Flattener, which will considerably improve your imaging performance. This corrector lens will flatten the final image over an 80mm diameter image circle on your Ritchey-Chretien scope.

    Given its large cell diameter, this ASA 4" Ritchey-Chretien Field Flattener will produce an 80mm image circle which is more than adequate coverage for a Kodak KAF-16803 CCD Sensor (which is 36.8mm x 36.8mm in size)! This ASA lens is somewhat different from their other correctors, in that it is fabricated from two lenses, each 92mm (3.622") in diameter, which can be integrated into a corrector system which is specific to the client's existing telescope and application! By adjusting the air space between these lenses, ASA can tailor this flattener lens to suit almost any larger Ritchey-Chretien telescope.

    Data obtained by ASA's physicist and designer, Philipp Keller shows that even at a field radius of 30mm, most of the energy contained within a well-focused star image falls within the Airy diffraction disk at a specific wavelength. The results are pinpoint stars from the edge of your CCD's field all the way to the center of the image. A (Ritchey-Chretien) telescope system with this field flattening lens installed will provide imaging performance which is much better than typical seeing limits will allow. Your star images will thus be limited primarily by seeing conditions at any given time.

    The pertinent dimensions of the ASA 4" Ritchey-Chretien Field Flattener are:

    • OD of mating surface, front cell barrel = 102mm (4")
    • OD of rear cell = 122mm
    • OAL = 55.61mm
    • ID of imager attachment, rear cell = 111.20mm
    • FFD = approximately 108mm (depends on telescope FL)
    • FFD (Flange focal distance) = Location of CCD plane behind flange
    • Moves focus back behind the original focal plane by only 4.57mm

    This ASA corrector lens is a special order item. Please email OPT or give one of our Telescope experts a call at 1-800-483-6287, to discuss details.


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