Need Macro Tube Guidance

I had a 100mm Macro lens but didn't shoot Macro seriously so it got sold being that my 70-200mm covers that range. However, there are times when I need that odd close-up (1:1 not mandatory). I do have the Canon 24-70mm which has a decent wannabe-a-macro feature, doesn't work all that bad, but sometimes I want to hit it a bit closer. I see that Canon makes a 12mm and a 25mm tube. Is the 12mm with the 70mm end of my lens enough to make a quarter or a dime look formidable? Obviously I'd rather get the 12mm for the price, but not if the 12mm barely does anything. If it DOES allow closer focusing then great! I'm not looking to read the serial number on the bottom of a cricket's left eyeball, just get closer than the lens does now. Any thoughts or experience with these things? BTW, my camera is full frame if that adds to the equation. Sorry, I do realize this is a bit of an ambiguous question!

Paul, I'm not sure if I can answer your question adequately because I'm not a hardcore macro shooter. However, I do use my 24-70mm with Kenko extension tubes on a crop body when I shoot frogs in Costa Rica. I find myself using the 12mm tube most often, and it provides decent closeups of poison dart frogs (which are pretty small).

Max

Thanks Max! Pretty much what I was hoping to hear. If someone replied and said "no no no, the 12mm does nothing, you need 25mm to even see the effect", then I'd spring for it. Looks like the 12mm will give me that small punch I need.
Thanks!

Paul, typically you can get 1:1 magnification by adding the same amount of extension (tubes) as the focal length of the lens that you are using (assuming full frame sensor); e.g., add 24mm of extension to a 24mm lens for 1:1; 12mm extension on 24 mm lens gives you wide angle close-up which can be an interesting look. so at the wide-angle end of your lens, the extension tube would work well. You can also add a close-up "lens" that you screw on to the front of your lens (just like a filter) without any light loss which you'll likely get with extension tubes. You can use both extension tubes and close-up "filters" together to get even more magnification. If you get the close-up "filters" go for the double-element ones (two pieces of glass) which are better than the single-element ones but they are not inexpensive. Canon has close-up "lens" - I'd suggest the 500D. Here's a review with a sample image taken with the 500D near the end of the review - http://www.photos-of-the-year.com/canon-macro/ You can also use teleconverters if you have any (again loss of light) and in combination with either extension tubes or close-up "lens". If you use the teleconverter and extension tube, put the teleconverter on the camera body first and then mount the extension tube on the converter (which will thus increase the extension) and then mount the lens on the extension tube. Hope that helps.
cheers,
David
www.rainbowspirit.com

I use the kenko 25mm uniplus tube on my D700 (full frame) with great results with my 24-70 and 70-200. - http://www.bhphotovideo.com/c/product/392234-REG/Kenko_UNITUBE25DGC_25mm_Uniplus_Tube_DG.html

There is a mathematical relationship between the lens and the extension tube. If you know the specs of your lens and the length of the extensin tube you can enter it in this calculator: http://home.comcast.net/~NikonD70/Tools/Simple_Close-up_Calculator/Simple_Close-up_Calculator.htm

I shot for years with a zoom and a set of off brand extension tubes. I highly recommend the set, because they offer a variety of extensions and you can adjust as needed. With a non-macro lens, you'll start to see image degradation as you approach 1:1, but if you use less magnification, the images will look good. An extension tube is hollow (no optics) so as long as they provide full capabilities for auto focus, depth-of-field preview, etc. there's no reason to pay the premium for Canon tubes.

Ditto to what Mark says about the off brand tubes (Kenko). You usually get a 12,20, & 35 tube in the kit and with no electronics, they are VERY light. You can also stack them to get more than 36mm of extension if needed. Also stack them while transporting & they are quite compact.

All great info, thanks everybody!