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07-22-2010, 02:16 PM   #1
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Extension Tubes

I have three extension tubes (original pentax ones) and am unsure about the difference between the three of them. The guy that I got them from said that he used them on the 120mm lense, and sometimes used them all at the same time. I'm not sure what the difference is between each extension tube, and when you'd use all three together.

Any help is greatly appreciated.

07-22-2010, 02:39 PM - 1 Like   #2
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extension tubes are used to change the maximum and minimum focus distances of the lens for close up work.

they are different lengths, and can be used individually or in any combination as desired based upon the magnification ratio desired.

as a simple point, 1:1 macro is achieved when the extenstion tube length is equal to 2 times the lens focal length and the subject is 2 times the focal length away from the lens.

the extension set tube you have is probably totalling 65mm and if used on a 120mm lens would let you achieve in total magnification of about 1:0.7, but you would have a very limited working distance range of only about 200 +/- 10 mm (as a guess)

there are tons of calculations available on the web for extension tubes.

you should seriously consider a tripod when using extension tubes
07-22-2010, 02:39 PM   #3
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Here is an overview for using extension tubes. They are for macro photography. The "poor-man's macro lens", as they say. The longer the tube, the closer you can focus. You can kind of have to just try the different lengths and/or combination of them depending on how close you are trying to focus on something.
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