Kenko Extension Tubes : Uniplus vs. Tube Set?

[Tony Printezis]

Hi all,


I'd like to get one or two extension tubes to improve the focusing distance of my lenses (mainly my 24-105 and my 70-200). I've been looking at the Kenko tubes. Does anyone know what the difference is between the two Uniplus tubes (12mm and 25mm) and the Tube Set (12mm, 20mm, and 36mm), apart from the set having difference tube sizes? Is 36mm pushing the limits of what an extension tube can do (given that Canon doesn't make one at that size)? And will I be OK with just the 25mm (potentially coupled with the 12mm)?


Thanks!


Tony

[Jon Ruyle]

With extension tubes, my philosophy is "the more the merrier". I have the kenko set, and can recommend it. I don't know about the uniplus.



Is 36mm pushing the limits of what an extension tube can do (given that Canon doesn't make one at that size)?


I'm not sure what you mean. Longer extension tubes will always allow you to focus closer. The 36 works very well. In fact, I often use the 12, 20, and 36 together (tiny bit wobbly with a heavy lens, but no practical issues). I wish there was a readily available 100mm extension tube.



And will I be OK with just the 25mm (potentially coupled with the 12mm)?


It just depends on how much maginification you want and what focal length you are using. At 24mm, the 12 and 25 together would give you well over 1:1 magnification (and little or no working distance), and would probably be plenty. On the other hand, at 200mm, even the 12+20+36 together won't even give you 1:1.

[Tony Printezis]

Jon,


Hi! Thanks for the comments.



I'm not sure what you mean. Longer extension tubes will always allow you to focus closer.


Well, as I understand it longer extension tubes might introduce vignetting. Also, do they cause the camera to only use a smaller part of the lens (i.e., the middle of it)? Depending on the quality of the lens, can't this reduce imagine quality?



It just depends on how much maginification you want and what focal length you are using.


To be honest, I don't know! I like using my 70-200 (f4 IS) for flowers etc. so from what you've said, the longer the focal length, the longer the extension tube that's needed to increase the magnification.


BTW, does it make sense to combine extension tubes with the 1.4x extender?


Tony

[Jon Ruyle]

Well, as I understand it longer extension tubes might introduce vignetting.


Vignetting is possible in principle, but when shooting closeups one typically uses small apertures, and thus it isn't a problem (if the aperture and ccd are both smaller than the inside of the tube, then no vignetting). In any case, I haven't had trouble with this.



To be honest, I don't know! I like using my 70-200 (f4 IS) for flowers etc


If you aren't sure or are shooting with long lenses, I would recommend the Kenko for more versatility and more total extension.



from what you've said, the longer the focal length, the longer the extension tube that's needed to increase the magnification.


The rule is: divide the length of tubes used by the focal length. Add this to the magnification (without tubes). This is the magnification with tubes. For example, if you have a 100mm lens and you add a 25mm extension tube, you get an additional 1/4=.25 magnification. If the 100mm lens started with a max magnification of .15, your new magnification would be .15 + .25 = .40. If it was was a macro lens (max magnification = 1.00), then your new max magnification would be 1.00 + .25 = 1.25. So the effect is more dramatic when used with lenses that don't already have good magnification. (That said, I often use tubes with macro lenses).



BTW, does it make sense to combine extension tubes with the 1.4x extender?


Sure. Extenders increase magnification (a 1.4x extender multiplies your magnification by 1.4 as well as the focal length). You get even more magnification if you put the extender between the 1.4x extender and the lens (I *think* that's right... I might be confused and it might be the other way around)

[Colin]

Well, I know that they can be too big if they move the focusing distance inside the physical space of the lens itself. At some point, it just don't work [:)]

[Jon Ruyle]

True enough, Colin. Short lenses often seem to have focal distances inside the lens when moved too far from the ccd.


Longer lenses don't suffer from this problem as far as I know. (You could put a mile of extension tubes on a 100mm macro and still have several centimeters of working distance).