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Archive 2012 · Help with using extension tubes for macros
  
 
mediahound
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p.1 #1 · p.1 #1 · Help with using extension tubes for macros


I have the 90 TS-E lens and just purchased a set of Kenko extension tubes but admittedly have no idea what I'm doing with regards to macros.

If I want to get roughly a 1:1 macro, which of the 3 piece Kenko set should I install?




Aug 08, 2012 at 02:01 AM
galenapass
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p.1 #2 · p.1 #2 · Help with using extension tubes for macros


Extension tubes increases lens magnification by an amount equal to the extension distance divided by the lens focal length.

For example, adding a 25 mm extension tube to a 90 mm lens will give a magnification gain of 0.277X. Now, if the lens's original magnification was 0.25X, then the new magnification will be 0.277X+0.25X=0.52X. I don't know what the 90 TSE native magnification is so you will have to use the principle above to figure it out.



Aug 08, 2012 at 02:11 AM
Ian.Dobinson
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p.1 #3 · p.1 #3 · Help with using extension tubes for macros


According to canon museum , the max mag of the 90tse is .29 with a mfd of .5m (always remember the mfd is from the sensor plane and not the front of the lens)

So looking at the Above formular you mag will be .56 with the 25mm on



Aug 08, 2012 at 04:53 AM
Ian.Dobinson
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p.1 #4 · p.1 #4 · Help with using extension tubes for macros


Assuming the kenko set has 36-20-12mm tubes I think the 36&20 together will get yo .91mag
And all 3 would be 1.04 mag



Aug 08, 2012 at 04:59 AM
 

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wickerprints
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p.1 #5 · p.1 #5 · Help with using extension tubes for macros


You know, the simplest thing to do is to just take photographs of a ruler. At 1:1, the markings on the ruler will correspond to the dimensions of the sensor, so for a 24x36 mm sensor, the image will show 36mm of the ruler along the longer dimension. Empirical measurement generally wins against theoretical calculation.

The bonus is that you will be able to determine with reasonable precision the resulting magnifications of all 8 combinations of the lens + tubes (including the case with no tubes). You may even wish to measure the minimum magnifications when using tubes--simply turn the lens to infinity focus (one way to do this precisely is to manually focus on a star at night), and then with various tubes attached, adjust the subject distance until the ruler is in sharp focus. You might need a fairly long ruler (or be able to measure an object with a tape measure), but you only have to do this once--afterward, you will know what ranges of magnifications each configuration will yield. And if you are really interested, you can use a tripod and measure the working distance at each min/max. It's a good exercise for anyone interested in macro photography.



Aug 08, 2012 at 05:13 AM
Imagemaster
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p.1 #6 · p.1 #6 · Help with using extension tubes for macros


http://www.fredmiranda.com/forum/board/45


Aug 08, 2012 at 01:55 PM
mediahound
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p.1 #7 · p.1 #7 · Help with using extension tubes for macros


Thanks for the information all, I appreciate!




Aug 08, 2012 at 09:02 PM





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