In article <4t7nj9$2e2@mars.mahidol.ac.th>, rakmt@mucc.mahidol.ac.th says...
>I consider extend macro ability on my 70-300 to 1:1. Since this one has
>magnification of 1:2, I'm in decision between Raynox macro explorer CM2000
>and extension tube. I know that extension tube give good quality but lost
>much light compare to Raynox. My question is/are..
> 1) How about the quality of picture Raynox produced compare to
>extension tube, compare at 1:1.
> 2) I quess that the depth of focus should be the same
>compare at 1:1 of two equipments, right?
> 3) How about the distance between lens and subject , compare at
>1:1 of two equipments.

Whether a tube or a good (usually achromatic) close-up lens will give
better results is very dependent on the particular zoom you are using,
so it is difficult to say without trying both on your lens. You can get
some idea, though, by comparing the image quality of the lens at the aperture and focal-length you want to use at mid-distance vs. minimum
distance - if the quality is definitely worse at closest focus, the
achromat will probably work better than the tube (though focusing the
zoom lens to infinity and using the tubes alone for close-focus can
often work well). Good achromats are made by Sigma, Nikon, Canon,
Minolta, and Leitz, I think. DOF will be the same at the same (close) magnification and aperture, independent of how you achieve it. The
greatest magnification with tubes will occur at the shortest
focal-length of the zoom; the greatest magnification with the
close-up lens will occur at the longest focal-length (but the CU
lens works by shortening the FL of the lens.....). Distance to the
subject at a given magnification will vary with the combination of
FL and close-up device used (a VERY long tube on the longest FL
will give the greatest distance, but will be impractical).
Use f11-16 for sharpest results.
Hope This Helps