That combination works very well together. The largest problem is
achieving focus lock. Pentax doesn't recommend the AF 1.7x being used
with lenses having a slower maximum aperture than f2.8. This results in
a maximum aperture equivalent to f4.6. Using it with an f4.0 lens gives
a maximum aperture of ~f6.7 which is 2/3 of a stop slower than the
slowest maximum aperture, (f5.6), I've ever seen on a Pentax auto focus
lens. At those apertures the cameras really struggle to focus in even
moderately low light conditions. However in bright light AF is no real
problem and the images are quite sharp.
On 11/10/2010 10:24 PM, Subash wrote:
hi,
does the pentax 1.7x TC work well with the A*300/4 (with the 'limited'
AF functionality it brings to manual focus lenses)? the user manual of
the TC does not mention this lens in the list of compatible lenses... if
things go as they should, i just might enabled with these two...
appreciate your inputs... thanks and regards, subash
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