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Would have been nice had you linked us to the thread you are talking about, so we know the context, but I'll take a crack at it... all lenses have a focal length, which is the minimum distance a subject can be seen in focus. say your camera lens can focus on a subject 2 feet away to infinity, but even at 2 feet the subject (snail eggs) is not enlarged enough to see properly. (even our eyes have a focal length; hold your fist out at arms length, then slowly bring it to one eye. where your fist goes out of focus is your eyes focal length, or around 6") you can't move your camera closer, or your photo will go out of focus, so what do you do? you get a magnifying glass which typically has a focal length of 0" to 10". have the magnifying glass focus on the subject, then 2 feet away have the camera focus on the image in the magnifying glass. get it? you've effectively enlarged the subject from two to ten times more magnification while still at the distance your camera can properly focus and take a good photo. A side point to keep in mind is many of todays cameras have a physical zoom and a digital zoom. the physical zoom actually moves the lens to the maximum magnification possible within a designated focal length, while the digital zoom does nothing more than enlarge the center of the digital photo stored in the memory of your viewfinder. so digital zoom really does not help if you are trying to take a detailed close up photo... and that's why "the magnifying glass trick" can come and save the day by enlarging and enhancing the detail of the actual subject itself, not just zooming into the digital image of it. BTW it's for this reason that many digital cameras with a close-up "scene" or "theme" mode setting, automatically disables the digital zoom while in that mode.
 
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