Do these
http://cgi.ebay.com/Extension-Tube-S...QQcmdZViewItem

scare anyone? They are like 1/8 the price of the ones adorame etc carry. It'd be with an old manual lens so no electrical contacts needed.

If they're really flimsy they could flex a lot or break with a heavier lens. Also if your camera requires any mechanical or electrical connection with the lens and those don't pass them through then you'll obviously lose some features.

Other than that you just have to be concerned with the lower quality air they likely used in the manufacture of these.

For that price, it's hard to say they wouldn't be worth trying. Looks like a set of similar lengths compared to the Kenko set which goes for about $170ish.

Looking closer, it seems you would have to shoot wide open. There is no method to pass the aperture controls.

with my tubes, it doesn't matter if i close my aperture. the DOF stays very extreme at all apertures.