Why are lens extension tubes useful?
When a photographer increases the distance of the lens further away from the body of the camera, it allows them to move closer to what they are photographing while at the same time keeping focus.
LENS EXTENSION & EFFECTIVE F-STOP
In order for a camera lens to focus progressively closer, the lens apparatus has to move further from the camera's sensor (called "extension").
The S8000 is impressively slim for a camera that packs a 10x zoom lens, but the gentle contour around the lens extension certainly helps make it appear even thinner than it actually is.
Converter/ Lens converter
Lens extension that increases or shortens the focal distance. (Macro-converter, tele-converter, wide-angle converter)
CPU
Central Processing Unit. The main processor of a PC (personal computer).
If your camera cannot meter in stop down mode, you'll have to use a light meter and factor in exposure compensation for the distance of the lens extension and use the camera in full manual exposure mode.
These are convenient but optically poor (get a cheap used set, which probably won't be any worse than a new set), even compared to lens extensions. If you're stacking them, put the most powerful (biggest number) one on first.
I hold the paper to the camera and read off the correction depending on lens extension. Calumet sells calculator sticks, which are rulers marked with the factors for different lenses.
[5] (Note that the magnification m here is negative for the common case where the image is inverted.) In photography, the working f-number is described as the f-number corrected for lens extensions by a "bellows factor".
 See also: Digital, Focus, Digital camera, Manual, Image
  
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