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    Celestron does not seem to be concerned about the focal ratio(F10-11) on their scopes. I know that in photography lenses, f stop (Aperture) is almost everything in terms of light gathering, why is this?

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    Quote Originally Posted by Kushla View Post
    Celestron does not seem to be concerned about the focal ratio(F10-11) on their scopes. I know that in photography lenses, f stop (Aperture) is almost everything in terms of light gathering, why is this?
    Most SCT's are designed to a baseline f/10 focal ratio. For imaging, they are adaptable to focal ratios between f/2 (i.e., replacement of the secondary with a camera/imager at the focal point of the primary mirror) and f/6-ish (use of a sub-aperture corrector, i.e. focal reducer). In addition to reducing the focal ratio, use of either technique also provides a wider FOV.

    In addition to this optical adaptability, these OTA's are normally mounted on moderate to high-precision GEM's for moderate to long-exposure imaging. The exposure duration makes up for the relatively slow focal ratio, while the mount's mechanical tracking precision (most often accompanied by auto-guiding) keeps the image field centered precisely over the exposure duration.

    The SCT is sort of a "workhorse", used for visual and imaging applications - while no one telescope design truly covers the span of applications, the SCT is close enough, and adaptable enough. The f/10 baseline doesn't pose a significant problem for an imager, and for a visual user it provides an adequate, if less bright/contrasty view.
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