Average Reviews:
(More customer reviews)I've had these for a few years now. They're built really well, and in all this time they have developed absolutely no signs of wear.
Tubes are really pretty basic in construction. There are no glass elements, just mounts on each end and a pass-through for the lens data terminals. These are well-built, and as such they fulfill their intended purpose - that being that you now have an easy, less messy alternative to taping a cardboard toilet paper tube between your lens and camera body (and yes, you can do that if you want to go the low-tech route. Just make sure you seal the light leaks!) Any other issues are likely to be caused by a misunderstanding of the tube's purpose, not by the tube itself.
There seems to be a lot of confusion regarding extension tubes, based on some of the reviews I've read. While it would be difficult, without diagrams, to explain exactly how an extension tube works and the effect it has on focus distance and magnification, I can at least try to help with some of the problems people seem to be experiencing in these reviews.
1) There are two distinct versions of these tubes. On the 36mm tube, you will see either "for C/AF" or "for C/AFs". The ones that say "for C/AF" do not support the Canon EF-S mount. They support only the EF mount. If any of your lenses are EF-S, then you will need the ones that say "for C/AFs". Functionally, they are equivalent, but the "C/AFs" models can mount both types of lenses. As of now, it is impossible for me to tell which version is being sold here. I have to assume that they are selling the "C/AFs" model.
2) Extension tubes do not "magnify", technically. They increase the distance between the lens and the sensor. Imagine a projector sitting a foot from the wall, projecting an image on that wall. Using a pen, you outline the outer edge of that projected image on the wall. That's the outline of your "sensor". The image fills the "sensor". Now add more distance between the projector and the wall (that's what an extension tube does). It's the same image, but now it's projected onto a larger surface, flowing over the boundaries of the "sensor". So now the "sensor" only records the part of the image in the very center, just enlarged due to the added distance from the projector.
3) Moving the lens farther away from the sensor alters the usable focus distance for that lens. Don't take these numbers as truth (it's just an example), but a lens that normally focuses from 3ft to infinity might focus from 6 inches to 2 feet, once the extension tube is put on. How drastic the change is depends on the length of the tube and the focal length of the lens (See the next point).
4) The lens focal length has a huge impact on the focus range, but not necessarily in the direction you'd think. Longer lenses (like 200mm or 300mm) won't see as much difference in focal range with the smaller tubes. While there is a difference, you still won't be able to get close enough to really improve the magnification significantly. Wider lenses show a more drastic change. I have used my shortest tube (least "magnification") on my 17-40mm f/4L. Even though it's the shortest tube, when zoomed out to 17mm, the camera will actually only focus INSIDE THE LENS. Meaning even if I lay a dime on the glass of my lens, it's still not close enough to be in focus. That's why so many people like to use their tubes with a 50mm f/1.8. It's a nice medium-length lens that can allow really close focus while still being usable.
5) There's no such thing as a free lunch! Remember the projector reference in #2? Well, just like the tubes, the farther that projector gets from the wall, the darker the projection will be due to light falloff. Meaning you will lose light when you use tubes. The amount you lose increases exponentially with the added distance from the sensor. So in many cases you will need to mount on a tripod or use external lighting. Also, any imperfections in the lens (aberrations, fringing, etc) will be effectively "magnified" just as much as the image itself. And the lens resolution limits will also be made much more obvious since the sensor will be recording a smaller section of the overall image circle provided by the lens. However, it's important to note that the benefits usually will outweigh the drawbacks, especially when the tubes are used within reason (i.e. I wouldn't do resolution-critical photos with all three tubes stacked together).
Hopefully this information is useful to someone. If I said anything confusing or if you see any mistakes, please let me know and I'll be happy to make adjustments/corrections/clarifications as necessary. But as far as the product itself goes, these are excellent, solid extension tubes with a great fit, no light leaks, and a nice light weight.
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Kenko DG Auto Extension Tube Set for the Canon EOS AF Mount.Extension tubes are designed to enable a lens to focus closer than its normal set minimum focusing distance. Getting closer has the effect of magnifying your subject (making it appear larger in the viewfinder and in your pictures). They are exceptionally useful for macro photography, enabling you to convert almost any lens into a macro lens at a fraction of the cost while maintaining its original optical quality.The extension tubes have no optics. They are mounted in between the camera body and lens to create more distance between the lens and film plane. By moving the lens father away from the film or CCD sensor in the camera, the lens is forced to focus much closer than normal. The greater the length of the extension tube, the closer the lens can focus.The KENKO AUTO EXTENSION TUBE SET contains three tubes of different length, a 12 mm, 20 mm, and 36 mm, which can be used individually or in any combination to obtain the desired magnification. Kenko also makes a UNITUBE 12 mm or 25 mm which can be purchased individually.Kenko's Auto Focus extension tubes are designed with all the circuitry and mechanical coupling to maintain auto focus and TTL auto exposure with most Canon lenses given there is enough light to activate the cameras AF system properly.Please Note;1. When using extension tubes the lens will not focus to infinity. The focus range will be greatly limited to a very close focusing distance.2. There is light fall of
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