3.5 with the 1.7x adapter gives ~5.6 as the maximum aperture so that
would make sense.
On 11/10/2010 11:01 PM, Subash wrote:
On Wed, 10 Nov 2010 22:47:46 -0500
"P. J. Alling"<[email protected]> wrote:
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.
that's reassuring to know. i guessed it could be because of the
slower f/4, though the user manual does list a f3.5 zoom...
thanks, subash
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