by ʇolɐǝz ǝɥʇ qoq

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The f/number is used to gauge the light passing power of a lens. The camera lens projects an image of the outside world onto the surface of the digital imaging chip (or film). The key factors are: Scene brightness, the sensitivity (ISO), the working dimeter of the lens (aperture), and the focal length. The f/number calculation is the focal length divided by ...


Yes. 5.6 becomes 8.0 If you add a 1.4x extender (teleconverter) you will now have a 140-560mm f/6.3-f/8 lens. Keep in mind that most cameras will only autofocus to a limit of f/5.6 and f/8 will be too dark for the AF to work. Newer high end cameras like the 7D Mk II and 5D Mk III will attempt to AF with f/8 lenses. Even if AF works (as in "the camera will ...


I have the Promaster Spectrum7 1.4x TC. Even at f5.6 plus the 1.4 TC my 7D tries to focus, sometimes it's successful, sometimes not, but often I get a soft image. I think because the Tokina 400mm F/5.6 is still recognized as that lens without the TC, and picks up on the MicroAdjustment setting I have set to correct the lens WITHOUT the TC. I'm assuming ...

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