Quote Originally Posted by Dan Fromm View Post
Ralph, back when I was a beginning photographer Modern Photography ran educational articles on roughly a two year cycle. Every other year they published a piece "Extension tubes of diopters -- which is better?" The answer never changed. Which is better depended on the lens. The only way to know which was better with the lens in hand was to try both. MP is long gone but I don't think the answer has changed.
Since this thread is asking about the Pentax 67, I'm not sure that my experience with the Pentax 645 is germane, but here goes. I own the Pentax 120mm AF macro for that system, a set of extension tubes, (13.3, 26.6, and 39.9mm), and a Marumi 330 +3 diopter achromat in 67mm. I've printed "eye-sharp" 24x30" prints at 1.5x magnification using both approaches. On a copy stand, I typically use the extension tubes, but on a tripod I chose the close-up lens because the camera balance was better.

I've used the 75mm f/2.8 with the short tube for some "near macro" work, as the 5.5:1 reproduction ratio of that lens can be limiting at times. Before I got the 120mm, I even tried all three tubes once. The results were reasonable, but I honestly feel the 120mm gives better results and is far more convenient to use.

So compared to a dedicated macro lens, whether you choose close-up lenses or extension tubes you're trading off convenience and some optical performance for cost. On "normal" lenses, I suggest using tubes. But once you reach focal lengths of 135mm or so, I suggest using close-up lenses instead.