Yesterday I received the Pentax Magnifier FB that I ordered from B&H.
It fits the *ist DS perfectly: slides over the eyepiece after removing
the standard rubber protection, flips up and out of the way for normal
viewing, then clicks down into place to allow precision manual
focusing. The ocular is rubber coated and turns for focusing. It's very
compact and doesn't get in the way when flipped up ... you could leave
it on the camera nearly all the time and not notice it, although it
will get in the way if you fit an external flash unit.
It makes doing precision focusing a breeze! Works especially well if
you are using wide angle lenses or doing macro work. $50 but well worth
it.
Godfrey