It can be used of course, but for these focal lengths the 1.4-L converter is definitely a better choice
Inquiring minds want to know - Why is it the better choice?
Ken Waller
The A1.4X-L and A2X-L teleconverters both have lens groups that protrude into the barrels of the lenses to which they are attached. As a result they only fit certain long lenses that have room for the prodruding lens groups. I'm not an optical designer, so I cannot say why this configuration is better, but I presume that Pentax engineers designed them this way for a reason.
--Mark
