Kenko Extension Tubes
Original article:
Kenko Extension Tubes
Updated: Mar 20, 2008
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.
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.
Source: ID=00242|kenko extension tubes, macro