For part 3 of this series, I will go over the use of extension tubes in relation to macro photography. What are extension tubes? They are simply spacers that one can put between the camera body and the lens of choice. By doing this you push the optics away from the film plane therefore increasing the size of the image, like when you look through a magnifying glass , the more you push the glass away the larger the image gets.
There are many different brands of extension tubes available: Canon, Nikon and Kenko just to name a few, Kenko are probably the most used by beginners, they are inexpensive and made well , you can get a set of three for the price of one of the other brands. Kenko tubes come in three sizes 12mm, 20mm, and 36mm for a total of 68mm of extension.
Depending on the brand and model you can purchase some that will maintain the auto focus of the lens and metering of the camera.
Advantages of using tubes.
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No optics inside of tube to degrade image quality
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Can be used on all lenses.
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Can increase image size on all lens even dedicated macro lens.
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Will allow all lens to focus closer but with the loss of infinity focus.
Disadvantages
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Loss of light
There is a formula for figuring the amount of magnification, based on the amount of extension used relative to the focal length of the lens.
Tube length, divided by focal length = added magnification.
Example, 50mm of extension divided by 50mm normal lens = 1 or 1to1, life size.
If you take a 50 macro that is already at 1to1 and add 25mm you get 2, Or 2x life size.
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In the samples below you will see a picture of a penny shot with a 50 f1.4 and 48mm of extension, I used the Kenko 36mm and 12mm: this is the closest I could get to 50 without going over. What I want to show you is the use of a 50 at 1to1 using tubes and then one with a dedicated macro that is already 1to1.
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50mmf 1.4 with 48mm extension
working distance 2"
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180mm Macro at 1to1
Working distance 9"
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For our next example, we will use our 100-300, 4.5-5.6 lenses with 68mm of extension and some real world shooting. Before we go to the pictures please understand that you can get the same effects with a 75-300 , 70-200 or 80-400 or any good zoom , as you will see the smaller the zoom the larger the image size or magnification, but also at a closer working distance.
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100-300 4.5, 5.6 w/ 68mm extension lens set at 100mm
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100-300 4.5, 5.6 w/ 68mm extension lens set at 135mm
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100-300 4.5, 5.6 w/ 68mm extension lens set at 200mm
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100-300 4.5, 5.6 w/ 68mm extension lens set at 300mm
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For this next example I will use this assortment of magnification enhancing accessories.
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500D
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Extension Tubes
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Extenders
Extenders are in effect, extension tubes with optics. They come in several powers; most common are the 1.4x and 2x. Nikon makes a new 1.7x. They can increase the overall power of your lens by 1.4, 1.7 or 2x for example. Take a 70-200 add a 2x extender to it and you get the effective focal length of 140-400mm. The addition of these can come in very handy for macro work.
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Here, I will show you comparative shots taken with the 70-200 f2.8 IS lens. All shots were with the lens set at 200 mm and the focus set at its closest focus distance. Accessories used were the 500D, 1.4x extender and 68mm extension tubes and a combo of all the above.
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The first image is with the 70-200 and 500D Flower dia. Is 9/16"
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70-200, 1.4x and 500D
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70-200, 68mm extension tubes
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70-200, 68mm, and 1.4x
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70-200, 68mm, 1.4x and 500D
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As you can see there is quite a variance in image size being created by the added tools for image size enhancement. There is not much advantage to adding the 1.4 to a lens when tubes are involved. Remember, the larger the lens the smaller the image size will be when using tubes. The advantage of the extenders is greater when used in combo with a diopter like the 500D. I won't go into anymore detail with the use of the 1.4 or 2x extenders, they are pretty self explanatory.
I hope you have enjoyed this part 3 of Macro for Beginners.
Tom Hicks
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Back to Part Two
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