Inspired by the best and cheapest lens thread, I was browsing lenses on B&H, and saw extension tubes listed. And it looks to me like the cheapest Pentax AF extension tube is the Tamron 1.4x teleconverter with lens removed, for $50. The tubes without lenses cost around $150.
What in the world is up with that? Does it really cost that much more to *not* grind, polish, coat, and install glass? -- "A nice adaptation of conditions will make almost any hypothesis agree with the phenomena. This will please the imagination but does not advance our knowledge." -- J. Black, 1803.
