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Occasional Contributor
Posts: 7
Registered: ‎10-18-2020

extension tube question

I need to know the inside diameter of the Canon 12mm extension tube

I want to use the extension tube between my 1.4X III teleconverter and my 100mm 2.8 L macro (which are otherwise non-compatible). I have read where people are using this combo successfully BUT the protruding portion of the converter will not fit inside my old set of Kenko extension tubes so I would like to know if it will fit with the Canon before buying the new extension tube.


I have the R5 and the focus stacking ability makes macro work even more fabulous so I want to take full advantage of the equipment I have.


Posts: 11,226
Registered: ‎08-13-2015

Re: extension tube question

[ Edited ]

".....I have read where people are using this combo successfully BUT the protruding portion of the converter will not fit inside my old set of Kenko extension tubes so I would like to know if it will fit...."


Somehow I doubt it.  The exact dimension is probably irrelevant.  If it fits a Canon mount, then another set of tubes will most likely have a similar size and fit.  Or in your case, won't fit.


Maybe you should ask the people who seem to have success.  But, before you do, I think you're chasing a something down a rabbit hole.  I think that you need to better understand how the gear works.  Let's forget about the claims of others for a moment.


Extension tubes work by decreasing the Minimum Focusing Distnce, which comes at the cost of a dramatic reduction in the Maximum Focusing Distance.  In other words, using extension tubes means you lose the ability to focus to Inifinity, or across the average size room for that matter.  A true macro lens already has a pretty short MFD.  


MFD is measured from the image sensor, not the front of the lens.  It is possible that you can shorten the MFD to the point that it is inside of the barrel of the lens!  It happens to people al the time.  We frequently get posts from people asking why can't they focus on anything when using extension tubes.  The reason is because they have stacked too many and the focus plane is inside of the lens barrel.


Using extension tubes with a macro lens means your will rapidly approach the point of diminishing returns.  The most likely outcome is that MFD will be reduced to the point that the lens is so close that ambient light will no longer be able to adequately light up your subject.  The lens will cast a shadow over the subject, which may require you add special lighting gear.


Canon teleconverters are made to work with specific telephoto lenses.  I do not think any macro lenses are included in the list of compatible lenses.  An incompatible lens may cause the camera to display an error message.  Nearly all of the compatible lenses have 300mm focal lengths, or longer.  One notable exception are the 70-200 lenses.


If you're using a third party, budget teleconverter, then it may "work" with your macro lens, or at least seem to.  the image quality of it is probably not on par with the Canon teleconverters, and the macro lens will only magnify those differences.


If you're still convinced that the setup should work, then I strongly suggest that you contact the people who claimed it works.  I do not think it will work, and your experiences so far have proven that to be true.  


"Doctor told me to get out and walk, so I bought a Canon."
Posts: 13,684
Registered: ‎12-07-2012

Re: extension tube question

You know I am not a big fan of any adapter, tel-con or tubes.


I agree with all that is said above because sometimes the trouble you go through just to get them to work properly isn't worth it. The more you try to push adapters or extension tubes the  more difficult it becomes until, like stated above, it won't work at all.

EOS 1DX and 1D Mk IV and several lenses!
Occasional Contributor
Posts: 7
Registered: ‎10-18-2020

Re: extension tube question

Thanks for the reply and sorry you had to go to all the trouble of describing the effects of teleconverters and extension tubes - I am VERY familiar with the optics etc. I also should not have said "I read" about this setup. I did read about it but also saw it being used in an online tutorial given by a professional photographer so I know it can be done. But in the tutorial, you did not see the "brand" or "model" of the converter or extension tubes I wish to find out :-) And the tutorial is several years old so not easy to get a response to a question although I have sent one of course. When it comes to "diminishing returns" - I don't know if you have done much macro work but any increase in magnification can be welcome depending on the set-up and with the 100mm lens you do have a little room to work with. So I've done lots of macro work using extension tubes in combo with my macro lens. And when I feel a need to use an extension tube with my macro the last thing I am worried about is not being able to "focus across the room" :-) Of course "lens shadow" is something everyone is aware of if they have ever tried macro work - I use a nice macro ring flash and portable light sources, reflectors etc depending on the situation to get around that issue.
In terms of lens compatibility with the extension tubes - I think the only reason for the "problem" is the physical mismatch. I only know it works with the macro-extension combo because I've seen the video of this professional using it. It works beautifully with my 100-400 L II.  Canon would have clearly had their engineers design a teleconverter for the "long lens user" market because that is certainly where the main demand is and why I have one. But the ability to combine with the macro allows for greater mag which is often what macro enthusiasts are "chasing" much of the time. Note that the inner diameter of extension tubes I already have not are perhaps just 1mm too narrow so a different model may very well be just big enough to fit so I am hopeful. Unfortunately, you can't go into most photography stores and try because so many of them don't stock extension tubes and I don't live anywhere near one of the very large camera store. I would note that "my experiences so far" are having a single brand of extension tubes - so I think it's fair to dig a little deeper than that before giving up :-)
Thanks again for your detailed response - I really do appreciate it. 

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