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General Photography
Macro
Questions about extension tubes
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<blockquote data-quote="480sparky" data-source="post: 566417" data-attributes="member: 15805"><p>Um, no it doesn't. If it is a 100mm lens without the tubes, it's still 100mm with them. Same thing when using bellows, or focusing any camera that uses bellows (folders, medium and large format cameras etc.)</p><p></p><p></p><p></p><p></p><p>Again, technically an incorrect statement. Well, maybe not 'incorrect', but certainly not based on optical physics.</p><p></p><p> Extension tubes and bellows don't do anything to a lens' focal points. Any lens has an infinite number of possible focus points at both paths along the optical line in 'front' and 'behind' the glass elements. What extension tubes do is allow one to choose a focus plane in 'front' of the lens that is closer to the camera by physically moving the lens further from the focus plane where the film of sensor sets. But the lens still has the same infinite number of focus points. Most are registered in the image as out-of-focus. Yet the focal length is still unchanged.</p></blockquote><p></p>
[QUOTE="480sparky, post: 566417, member: 15805"] Um, no it doesn't. If it is a 100mm lens without the tubes, it's still 100mm with them. Same thing when using bellows, or focusing any camera that uses bellows (folders, medium and large format cameras etc.) Again, technically an incorrect statement. Well, maybe not 'incorrect', but certainly not based on optical physics. Extension tubes and bellows don't do anything to a lens' focal points. Any lens has an infinite number of possible focus points at both paths along the optical line in 'front' and 'behind' the glass elements. What extension tubes do is allow one to choose a focus plane in 'front' of the lens that is closer to the camera by physically moving the lens further from the focus plane where the film of sensor sets. But the lens still has the same infinite number of focus points. Most are registered in the image as out-of-focus. Yet the focal length is still unchanged. [/QUOTE]
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