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Archive 2013 · Extension tubes -- max. magnification?

  
 
warthog
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p.1 #1 · p.1 #1 · Extension tubes -- max. magnification?


Sorry in advance for a question that will show off my ignorance, but I appreciate any input you all can give. I have a project that requires me to take macro pictures of some very small electrical components. I have a 5dII body and a full set of Kenko extension tubes (36mm, 20mm, and 12mm). My question is, which of my lenses in combination with which tubes is going to give me maximum usable magnification? The target components are going to be on a test bench, and focal plane depth is not a major consideration.

A web search yielded the equation "Additional Magnification = (Extension Tube Length)/(Lens Focal Length)" My available lenses are:

20-35 f/2.8L
28-75 f/2.8 (tamron)
24-105 f/4L IS
50 f/1.4
85 f/1.8
90 ts f/2.8
135 f/2.0L
70-200 f/2.8L IS I
70-300 f/4L

Is it as simple as the 20-35 at 20mm paired with the three tubes together (68mm) is going to have max magnification (68/20 = 3.4x magnification)? Or is there more to it than that?

Thanks in advance for any thoughts; no answer is too basic as I've only ever messed around with macro stuff on a whim. The only lens I've used so far is the 90 ts, because it is manual focus and seems to give the finest manual adjustments.



May 20, 2013 at 01:56 PM
Imagemaster
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p.1 #2 · p.1 #2 · Extension tubes -- max. magnification?


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


May 20, 2013 at 01:58 PM
warthog
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p.1 #3 · p.1 #3 · Extension tubes -- max. magnification?


Thanks. I've re-posted my question in the macro forum.


May 20, 2013 at 02:38 PM
acjd
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p.1 #4 · p.1 #4 · Extension tubes -- max. magnification?


Do the math.

Go here and find your lens. Find the original magnification. Then go here and plug the numbers in the first calculator. Done



May 20, 2013 at 02:44 PM
Ian.Dobinson
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p.1 #5 · p.1 #5 · Extension tubes -- max. magnification?


acjd wrote:
Do the math.

Go here and find your lens. Find the original magnification. Then go here and plug the numbers in the first calculator. Done


+1
I was just about to post the cambridge link . its very helpfull.

also its best to work out what the true focal lenght of any lens is first (by setting the tube to 0). then add the tube size in

eg the canon 24-105 in your list has an MFD of .45cm with a mag of .23 . but if you look at the calc that mag @105 mm would give a MFD of .69cm
so in fact its tru focal length can be worked out as 68.5mm

so now you know that you can work out what each tube would give
12mm = mag .41 mfd 33cm
25mm = mag .59 mfd 29cm
36mm = mag .76 mfd 28mm

also dont forget the MFD is taken from the sensor not the front of the lens .



May 20, 2013 at 05:10 PM





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