# Kenko extension tube help



## gngan (Mar 8, 2011)

Hello,

I just bought the Kenko extension tube DG. I am not sure if it's working properly or not. I test it on 550D with 24-105. I find it hard to auto focus with 12 and 20mm (tube). It will focus on a particular distance and not focus with other distance. I tried MF and it will only focus on a particular distance. I can't take normal pictures when the tubes is/are attached.

I tried stacking 12 and 20mm tube and it focus with particular distance. When i tried the 36mm; it can't AF/MF. I tried stacking all three but can't AF and MF.

Then i tried it with with my 10-22 lens and it can't AF/MF with any of the tubes but DG is suppose to be compatible with EF-S lenses.

Am i not using it correctly or the tubes aren't working?


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## Leisersan (Mar 8, 2011)

What are you trying to accomplish using the tubes?


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## Jamesy (Mar 8, 2011)

Not 100% but the tubes might be putting the focus inside the lens. I have a 17-55/2.8 and Kenko tubes and I cannot use them together. My 50/85/135 primes work great with tubes as well as my 70-200 f4/IS. Try a longer focal length lens and see if that works.


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## Admin US West (Mar 8, 2011)

gngan said:


> Hello,
> 
> I just bought the Kenko extension tube DG. I am not sure if it's working properly or not. I test it on 550D with 24-105. I find it hard to auto focus with 12 and 20mm (tube). It will focus on a particular distance and not focus with other distance. I tried MF and it will only focus on a particular distance. I can't take normal pictures when the tubes is/are attached.
> 
> ...



Tubes are very limiting, you can easilly lose 2-3 stops of light which means a f/4 lens becomes f/8 or f/11, not enough light to autofocus. You can only focus with a tube when the lens is close to the subject. Don't expect to focus a few feet away. With a EF-S lens you are likely liited to a very close focus distance.

http://www.thkphoto.com/products/kenko/slrc-04.html


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## gngan (Mar 9, 2011)

The longest focal length i have is 24-105 and that's why i am worried if the 36mm tube isn't working. Let me try the 50mm prime and see if it works. When you guys say close focus distance; do you mean the distance between the lens and the object or the distance in the view (zoomed) and the object?


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## gene_can_sing (Mar 9, 2011)

The extension tubes are not user friendly at all. Auto focus does not work really. For Macro stuff, you should just manual focus, even on the expensive macro lenses, most people just manual focus with macro.

There are only certain Canon lenses that work with Extension tube. Do a google because I know there is a list of the working lenses.

My advice, just get a real macro lens. The tubes are just not worth the headache. Also, you have a very set distance that you can focus on with the tubes. Very limiting.


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## gngan (Mar 9, 2011)

That sucks. I've searched for a pretty long time and thought it should work. The problem i have with my Kenko is that the 36mm tube can't AF/MF with my 24-105. I googled "compatible lens for extension tube" but nothing showed up. Do you have any link?


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## nismohks (Mar 9, 2011)

i have the kenko extension tubes too and i use it with my 7d

for the 10-22 any one of the extension tubes will put focus inside the lens. ie. u wont be able to focus anything at all even with using the shortest tube since the camera would never be able to get close enough to the subject to be able to get a focus on. if u have a kit lens 18-55 or something try using that @50mm+ and it should work.

with the 24-105, area u trying this with the lens set at 24? if so, u will also encounter the same issue.

i dont have the 24-105, but with my 24-70 the minimum focal length i need in order to be able to focus when using the 36mm is at 47mm and with the lens right up against my subject (in my case a screw on one of my lenses)

so try redoing your tests with the zoom set at the long end and then gradually work wider to find the minimum required distance. more likely, it is because the extension tubes are moving the minimum focusing distance so close that the theoretical point would be inside the lens. 

you have to consider that the focusing distance is not measure from the end of the lens to the subject. it is from the sensor to the subject.

let us know how u go


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## gngan (Mar 9, 2011)

nismohks said:


> i have the kenko extension tubes too and i use it with my 7d
> 
> for the 10-22 any one of the extension tubes will put focus inside the lens. ie. u wont be able to focus anything at all even with using the shortest tube since the camera would never be able to get close enough to the subject to be able to get a focus on. if u have a kit lens 18-55 or something try using that @50mm+ and it should work.
> 
> ...



Thank you very much for the suggestion. The 36mm tube can focus on 24-105 (set as 60). I am a little disappointed that 10-22 can't be used. Does that mean you will at least 50mm+ in order to focus properly with tubes?


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## nismohks (Mar 9, 2011)

yer the 10-22 is just too wide for extension tubes to be used.

for my 50 f1.4 using the 36mm i can focus on something 7cm away from the front of the lens, but nowhere before and after.

my 24 f1.4 will focus ONLY with the 12mm and thats with the lens pressed up against the subject.

my 10-22 will not focus with any tubes

dont worry about your tubes being faulty. the issue you are seeing is a technical limitation. if you are still concerned for the EFS usability just find any other EFS lens and it will work. ive used my tubes with my mate's efs 17-55 f2.8 and my old 17-85 f4-5.6 so they definitely work


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