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Margo, this "tele-extender" - in effect - DOUBLES lens focal length, as you know... The problem, then, is that - while you get a bigger image - you DECREASE the effective "light-gathering power", that-is (like in telescopes) the "F - RATIO" is doubled. I don't mean to "talk-down" to you, if you already know this. Simple fact is, that you will DOUBLE the size of the image - but that DECREASES the light reaching your sensor (FILM, in the old days) - by a FACTOR OF 4 . In camera-talk, you "lose 2 f-stops". If your lens is F/ 4, then this 2X "doubler" makes the F-ratio F/ 8 . So - for "action-shots" you'd better have a "big glass" lens , or else be shooting in bright light ... Good Luck, I've been there... -Mark T
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