what extension tube?

[t5Nitro]

What extension tube would I want to make the 100mm macro give even more extreme macros?

Would anything make it able to be similar to the mp-e65? The lens alone is just costly for me.

[Canon Bob]

To give you a rough idea, you'll need 56mm of extension tubes to double the maximum magnification....ie 2:1

Bob

[ben_r_]

No, you cant really match the MP-E 65mm, and even if you did you would need something the Canon twin light flashes just to have enough light to see anything and take a picture. There really isnt a substitute for the MP-E 65mm, its a highly specialized lens. You could how ever try getting a reversing filter ring and putting a 50mm backwards on the from of your 100mm macro. I have seen other do that and get some pretty good results. Check out the macro section and try posting this question in there.

[t5Nitro]

I wasn't quite sure how close the mp-e65 lens actually did. I just found some picture samples from it and that's extreme. I just wanted to go further than what the 100mm macro could do.

Is this what I would want to start out with?

http://www.bhphotovideo.com/c/product/375102-REG/Kenko_AEXTUBEDGC_Auto_Extension_Tube_Set.html

[Wilt]

Any extension used will get you closer than what the lens does by itself! The amount of extension will determine what reproduction ratio (magnification) can be achieved with the lens focused at 'infinity', and the built in focusing mechanism of the lens permits it to get even closer.

Reproduction ratio is simply determined as [extension tube length]/focal length

So 25mm tube on 100mm FL is 1:4 (image on sensor is 1/4 actual size)

[bigrig]

Is this what I would want to start out with?

http://www.bhphotovideo.com/c/product/375102-REG/Kenko_AEXTUBEDGC_Auto_Extension_Tube_Set.html
I don't own any tubes yet, but I am shopping around. I have heard some say that since they're just "air" inside the cheap ones aren't much different. Here's a set with metal mounts for about half that price - http://www.adorama.com/MCAETEOS.html

[ben_r_]

I had the Kenko ones (which are the most popular third party option) and didnt like how the metal grinded against the camera mount or lens. So I sold those and bought the Canon ones.

[krb]

The tubes are "just air" inside so you don't need expensive ones. But if you are using an EF lens then you will likely want the tubes to provide electrical connections so that you can change the aperture.

Most people get the Kenko set.

[KCMO Al]

Yes, but the Canon tubes contain "L" air. Vastly superior.
I own the Kenko ones and do not experience "grinding." They work very well and are a really great, relatively inexpensive accessory for any lens combination, and are really effective with macro lenses.