What is Extension Tube?
Extension Tube is a great and comparatively inexpensive way to get started in macro photography. You can match it with a nifty fifty (50mm F1.8 lens) and get more than 1:1 magnification. You can also use it with your existing 1:1 macro lens and go beyond 1:1 magnification (life size). Extension Tube is available in Canon mount, Nikon mount, Sony mount etc. If you are not sure whether you really like macro, this is a good way to test the water and to get your feet wet.
It looks like this and normally consists of 3 tubes of 12mm, 20mm and 36mm.
What lens is the Extension Tube compatible with?
It works great with macro lenses such as the Tamron 60mm, Canon 60mm, Canon 50mm F/2.5, Nikon 60mm F/2.8, Tamron SP90, Canon 100mm, Nikon 105mm, Sigma 105, and even Sigma 150mm. Kenko Extension Tubes set consists of three tubes of different lengths: 12mm, 20mm and 36mm.
How does Extension Tubes work?
Extension tubes allows a lens to focus closer than its normal set minimum focusing distance. That has the same effect as magnifying your subject i.e higher magnification. Extension Tube will enable you to convert almost any lens into a macro lens at a fraction of the cost while maintaining its original optical quality.
How many Extension Tubes should I use?
A set of Extension Tubes consists of a 12mm, 20mm and 36mm tubes. You can use either just one, or any two, or all three together to achieve different magnification. The longer the combination you use, the higher the magnification you can achieve. Extension Tube works on non macro lenses too: 50mm f/1.8, 70-200, 300mm, 400mm etc.
Any IQ degradation?
There are no optics in the Extension Tubes so there will be little or no IQ loss.
What Magnification can I achieve?
Magnification achievable when using Extension Tubes with 1:1 macro lens. Thanks to KJTeng for some of the info on magnifications here:
With Tamron SP90, Canon 100mm, Nikon 105mm - approximately 2:1 (2X life size)
With Nikon 60mm macro - approximately 2.53:1 (2.53X!!!. Add a 1.4X Teleconverter and it will be more than 3X)
With Sigma 150 - approximately 2:1 (2x life size), this is a little surprising!
Magnification gained = length of tubes / focal length
For example, with the nifty fifty 50mm F1.8 and full set of 68 mm of tubes
Magnification gained = 68/50 = 1.36X.
Obviously this doesn't really apply to macro lenses. Therefore the best way to find out is to shoot an mm scale ruler as explained in this post.
Only two types of tubes!
Yes, only two types, basically, if you ignore the brand names.
i. those without electrical circuitry nor mechanical coupling - you get a set for less than USD10 if you know where to look! No TTL, no AF.
ii. those with electrical circuitry and mechanical coupling -these will cost more, obviously, but I highly recommend it though. Unlike the type with no electrical circuitry and no mechanical coupling, you can still control your aperture freely, and your view finder won't be dim either because you don't have to pre-set your aperture to the usual macro setting of normally F11.
Your ETTL will still work as normal too! This is very important because it takes a lot of lighting guesswork out of the equation. I almost always shoot in ETTL mode, and use FEC to control my light.
There are many other brands other than Kenko. Google is your best friend so do your homework!
Add a 1.4X Teleconverter for even higher magnification - roughly another 0.4X to whatever you get from the extension tubes!
Finally, if you want even higher magnification, like 3X to 5X, then you must check out DMF SuperMacro!