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Tip of the Month

Easy Macro with Extension Tubes and Zoom Lenses

October 2011

steller jay feather
I didn't have a macro lens with me in Yellowstone, but with a 25mm extension tube
and my 28-300mm zoom, set at 50mm, I still had a half-life-size image of this Steller's Jay primary feather.

Cropped, with some sharpening added via NIK Sharpener Pro, gives me a real macro image, in the order of about 1:1 or greater.

Macro photography implies 1:3 magnifications or greater. True macro lenses usually focus down to a reproduction ratio of 1:1 or 1:2, but near-macro is often considered a higher ratios, of 1:3 or 1:4. These numbers can be considered like fractions, with 1:2 referring to 1/2 life size, 1:3 as 1/3rd life size, etc., based upon film or a full-frame sensor. Crop factors on smaller sensor cameras will actually make the image appear greater than these ratios, but again, that is because of the crop factor.

Extension tubes can transform a close-focusing lens into a macro, or near macro lens, by 'extending' the minimum focus. Doing so, you'll be able to focus closer to your subject but at a cost, as the distance focus is compromised. With a narrow extension ring and a big telephoto that loss of distance may be almost unnoticeable, as it would be if you added a 12mm tube to a 600mm lens with a 2X converter behind it. But at the other extreme, say adding a 25mm extension tube to a 70-200mm zoom, you'll definitely lose infinity focus and, at 70mm, may not have focus further than 6 feet or so.

The trick behind using extension tubes with a zoom lens is to understand the following:

Magnification Ratio = length of the extension tube/length of prime lens

Consider this, if you have a big image size, or a big magnification ratio like 1:2 or 1:1, you'll have a big image size. At any given focal length, wouldn't that imply that to get a bigger image you would have to get closer? Without using a tube, if you wanted a bigger image size you would simply move closer, until you reached your minimum focusing distance. Accordingly, if you added an extension tube, allowing you to extend your minimum focus and get closer, you'll have a greater magnfication.

But here's the rub. Minimum focus varies by the focal length, and if you simply slap on an extenstion tube you might get results or, as we've often seen, you just can't get the combination to work. Now, consider that formula above and think this through. If you had a 25mm tube and a 70-200mm lens zoomed to 70mm, you'd have 25/70, just about a 1:3 magnification ratio. That's a pretty large image size compared to a 1:8 ratio, as you'd have if you zoomed to 200mm (25mm/200 = 1/8), and to have a bigger image (1:3) with a smaller lens (70mm) it stands to reason you would have to be closer, right? And you will be, with the front element of the lens less than 6.5 inches from the subject! At 200mm, and 1:8, your working distance will be 24 inches or so, which is a far more comfortable distance.

The maximum focusing distance changes, too, and at 70mm that maximum distance is essentially the same as the minimum distance, 6.5 inches or so, while at 200mm it extends a bit past the normal minimum focusing distance of 4.5 feet. So, what does this mean?

Well, if you're zoomed to 70mm you must be 6.5 inches away. If you're zoomed to 100mm, you'll be further away, but not as far away as you'd be when zoomed to 200mm. You can 'tweak' image size (reproduction ratio) and working distance by zooming in or out, and if you know the working range with your extension tube you can use the extension tube and lens effectively. For example, with my lens I'd have a working distance range of infinity to 4.5 feet without an extension tube, and 6.5 inches to about 5 feet with an extension tube, depending upon where the lens is set on the zoom and, towards the 200mm end, whether the lens is focused at the minimum distance or towards infinity.

Where people get into trouble is when they forget this, and try to get the image in focus when they're too close for the focal length, or too far away. If you can remember the basic range you have with the tube, as in my case 6.5 inches to 4.5 feet, and you are within that range, then by zooming, and perhaps focusing, you'll pop your subject into focus. Or you can simply move in or out until the subject pops into focus, based upon the focal length you're using.

Perhaps this is elementary to you, but believe me, I've so often heard participants of our Digital Complete Nature Photo Course say that they have extension tubes, but they don't know how to use them! Some say that they worked the one time they used the tubes but then wouldn't work the next time. Why? They were either too close or too far away for the focal length in use.

Understanding this, you can use a zoom lens as a substitute macro lens when carrying a macro is impractical. When we travel by air, to India, Kenya, or Yellowstone, where we suspect little use of a true macro lens we'll bring along a 25mm extension tube instead. Then, if we need to get close and to near macro ranges, we can do so with the tube and a zoom. And, if I need to get closer to a bird or mammal or reptile or flower and I'm using my 500mm telephoto, I can add the extension tube and focus closer. I won't reach macro ranges (25/500 = 1:20) but I will be able to focus closer.




Previous Tips, July 2009 onward


FotoSharp Camou Rain Covers
Canon 17mm T/S Lens
Locking Button for the Canon 7D

NIK HDR Program

Silver Efex Pro for Black and White Images

Beware the DELL Software Solution Rip Off
How and What We Pack for Trips

Canon Digital Learning Center

The Movie Mode with the Canon Mark IV
Batch Renaming in Bridge and CS5
Alternate Uses of some Bogen Products

Hoodman Products

Using High ISO and Live View for Focusing in Dim Light

Art Print Scams for Hungry Photographers

Hungry Vultures ruin vehicles in the Everglades

Use a Short Lens for Depth of Field

Get Professional Help!

Mini-Molar Bag
Access America Trip Insurance
Bogen Base for Macro Work

Archived Tips of the Month
prior to July 2009
Most of my original Tips of the Month for the last several
years are available through this link. The 'look' is from my
original web site, although if I ever have enough time I might redo these pages to match the new web site But that's not a high priority.