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Old Jan 22, 2013, 10:01 AM   #1
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Default Best focal length for .....

What is the best focal length to have when you are using extension tubes ? Is a 50mm focal length better than say a 100mm ? Which focal length will give you the biggest magnification ? Thanks.
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Old Jan 22, 2013, 10:24 AM   #2
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For a given extension tube, the shorter the focal length, the bigger the magnification gain using that tube. OTOH, at some point the tube becomes too long for the focusing distance that would result from using it -- which is generally shorter with shorter focal lengths.

[ETA: This tutorial: http://www.cambridgeincolour.com/tut...es-closeup.htm includes a calculator to allow you to determine how the focus distance and magnification changes with extension tubes.]

Last edited by tclune; Jan 22, 2013 at 12:00 PM.
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Old Jan 22, 2013, 10:59 AM   #3
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What do you want to shoot?

For macro work, the most important consideration is focal length, and you select the focal length based on what you want to shoot.

I've enjoyed great success with a 70-210mm f/4 1:4 "macro" lens with a 12mm extension tube.

Back when I had my Minolta SRT-101, Rokkor 50mm f/1.4 lens, and Vivitar bellows, I was looking through the viewfinder when a fly landed on the objective lens. All I saw was the six legs attached to the out of focus body. Before I realized what I was looking at and could press the shutter release, it flew away.

Remember that, while extension tubes contain no optical elements of their own, they magnify the flaws in the lens you use them with.
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Old Jan 23, 2013, 4:10 AM   #4
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Using the same tube length, the shorter focal length will always give the greater magnification, but at a closer distance.

Assuming you are getting the autofocus tubes, just start with a lens you have. That's the advantage of the auto tubes. You don't have to buy a lens to go with them.

If you use the "blank tubes", like some of us do, then you need a manual focus, manual aperture lens or a lot of functions don't work. That's fine with the liveview m4/3, but a lot of dslr users don't like that setup.

As long as you have a typical kit zoom or 50mm prime or longer zoom to use, you should be ok to start using the auto tubes like the Kenko.
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Old Jan 23, 2013, 6:31 AM   #5
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Using extension tubes means you'll probably experience some light los, so the viewfinder will be dimmer. If you'll be using a dim lens with the tube(s), it could get pretty dark in there. The kit lens is pretty dim at 55mm, which is why many use tubes with faster lenses.
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