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PHOTOKID

03/16/2007 06:16:30 AM · #1

Hey all,

Could someone please give me a quick run down on how to use an extension tube. Such as, what happens as your extension tube length increases and basic ideas of magnification(as the length goes up mag goes up?)

Thanks
Rich

ralph

Nikon Z9

03/16/2007 07:45:04 AM · #2

a short answer;
the lens projects light against the sensor
so further away the projection is larger (and a drop off of light increases)
thus you get magnification

dwterry

Canon EOS-1D Mark III

Canon EF 24-70mm f/2.8L USM

03/16/2007 08:10:26 AM · #3

Extension tubes allow you to move closer to your subject. The trade-off is that you lose the ability to focus on infinity. So extension tubes are used for macro work. The longer the extension tube, the closer you can get to the subject, and the larger the subject becomes. Add an extension tube to a lens that is already capable of 1:1 macro (such as the Canon 100mm 2.8) and you've got an awesome combination.

PHOTOKID

03/16/2007 08:55:55 AM · #4

Thanks Guys,

So for kind of small stuff I need a short extentsion tube and the smaller it is the larger I need. Got it.

Thanks
Rich

hyperfocal

Nikon D7000

Nikon MF 105mm f/2.5 AIS

03/16/2007 09:17:05 AM · #5

FYI the needed extension to get to 1:1 is equal to the focal length of the lens (focused to infinity), so with your 50mm f1.4 that would take 50mm extension tube. If you put that same 50mm on your Tamron and you would get close to 2:1 @ 28mm and about 3/4 life size @ 75mm (@ infinity). It depends on the focusing mount of the lens exactly how much magnification is possible. Also many modern IF lenses uses focal length shortening as if focuses closer, so the magnification increases more than you would expect for the stated focal length. For example the focal length of the Nikkor AF 105mm f2.8 macro is only 60mm @ its minimum focusing distance.

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