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Kenko Extension Tubes

Original article:  Kenko Extension Tubes

Updated: Mar 20, 2008

Kenko Extension Tubes - Photo: Those of you, who have been keeping up, know that I have been experimenting with macro photography. At first I looked at the dedicated macro lens offerings from Canon and Sigma respectively. Obviously as with anyone else, cost is a consideration; but not the only consideration for me. Since I enjoy the outdoors and traveling, many of my photographic subjects are, well, you can guess, around the outdoors and travel. There is an adage that I try to live by - pack light, no I mean really light - problem is photography and packing light do not necessarily go hand in hand.

Kenko Extension Tubes with end caps - Photo: So for me weight and bulk of equipment are also a real consideration. Seeing how large dedicated macro lenses can be gave me pause, after all on most days how often are you going to pull out your macro lens? With just the basic gear of mine, I'm already carrying more than I want; cutting back where I can on other things packed. But there is only so much weight you can save by changing your toothbrush for a traveler’s toothbrush, and even less weight saved by sawing that traveler’s toothbrush in half. Trust me, I don't need a scale to tell you that the weight savings don't add up to another lens.

My research led me towards two alternative options for macro photography: a screw on macro filter and extension tubes. The great benefit of both these approaches is that you can take almost any existing lens and give it some macro capabilities. Double duty. The downside are they are not as easy to work with and some light loss. I opted to try the extension tubes, mainly because I have been fighting with the screw in filter holder that I already have and didn't want to add more to that frustration. (I mention the screw-in filter for your benefit and consideration - Canon 500D is an example (Nikon users don't fret, there seems to be more Nikon users of the Canon 500D than Canon users)).

Minimum Focusing Distance
Kenko makes an 'auto' extension tube version for Canon, Nikon, and Minolta mounts - in other words, it has electronic pickups so your camera can still auto focus, set the aperture, and do the other electronic computerized magic that it does. These Kenko tubes seem to be the de facto standard. The Kenko tubes can be purchased as a set that includes 12mm, 24mm, and 36mm lengths – each length can be used alone or in combination. The extension tubes sit between the SLR body and the lens, by moving the lens further away from the sensor the minimum focusing range is moved closer. I'm not sure why this is so, I don't believe it's important, although I keeping wondering why this is so, I'll let you know if I figure it out. The reason that it works on most lenses and not all is that if you mount extension tubes to a wide angle lens the focusing range is beyond the front glass of the lens. In other words that bug you are trying to shoot would not only have to be smashed against the front of your lens, but it would actually have to be inside your lens to be in focus.

Maximum Focusing Distance
Keep in mind, the extension tubes not only change the minimum, but also the maximum focusing distance. You would have to have that bug about 4 inches away with the 50mm and the 24mm extension tube mounted; 3 inches away and you won't be able to get it into focus, 6 inches away and you won't be able to get it in focus. Get it? The extension tubes create a focusing zone. The longer the extension tube the closer the zone is to the front of the lens. Setup and composition take time as you swap out tubes and move your tripod around. Your friends will be tapping their feet waiting patiently as you try to shoot your buggy subjects - on second thought you better go out into the field alone or with other photographers while you get the hang of your extension tubes and lens combinations.

Lens Focal Length Matters
Keep in mind, the longer the focal length of the lens the further away the minimum distance is. So while your buggy subject is in focus 4 inches away from the 50mm, he will be 6 inches away from the 85mm. The reason that the 70-200mm zoom is a popular lens to use extension tubes is that you can change the focal length by zooming (without the lens changing length dimensions). So instead of moving your tripod around you can make adjustments with the zoom. I really recommend using the zoom approach when learning how to use extension tubes, if you have the appropriate zoom - one that does not expand in length as you zoom in and out.

Exposure Compensation
As mentioned before there is light loss when using the extension tubes. You will need to compensate for this by stopping down. There doesn't seem to be any exactness as to how much you need to stop down. I myself am still experimenting with this. Apparently the longer the tube, the more light loss, the more you will need to compensate the exposure.

So far I'm really sold on the extension tube as a good alternative option to a dedicated macro lens. The tubes contain no optical elements; they are just spacers between the SLR and the lens. They don't add much weight to my already heavy pack and I've gotten results that I'm really happy with.

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