Ext Tube vs. Closeup Lens

[wordsandpictures]

I've been experimenting with different lens/extender combinations and just wondered if anyone could shed light on the question of using a Proxar F=1m on my 150mm Sonnar vs. using a Model 21 Extension Tube on the 150mm. I have not done extensive side-by-side testing yet, but the two approaches seem to yield similar results.

I'm tending to lean toward the extension tube approach because it allows me to work slightly further from the subject. I don't think depth-of-field is an issue because I'm working under very powerful studio lighting. All things being equal, will one of these approaches result in a sharper image?

[elkhornsun]

With the closeup lens you are adding magnification and reducing DOF and image quality,  though maybe not enough to notice.

With the extension tube you are changing the f-stop and the close focus distance. I would expect better image quality with the extension tube. George Lepp has made great use of the extension tube with telephotos and wide angle lenses for close up work.