This page shows how the Pentax-A 120mm f/4 performs on the demanding mosaic target.
I took an immediate liking to the Pentax 120mm f/4. I used a loaner from a reader. It’s solidly built, and it uses an old-style focusing helicoid with plenty of “throw” for fine focus adjustments, all the way to 1:1 on a 44 X 33mm sensor.
I haven’t tried the autofocus FA version, but I doubt that it will compare favorably for manual focus, because AF lenses are usually a compromise in ergonomics, lacking a focusing helicoid.
Using the AF focus assist on the 645D consistently results in front focus and thus a blurred subject. This is true with the 120/4, and with other lenses I tried. Caution advised, and use of fine focus adjust feature might help (not yet tested).
For this test, I focused manually with 3 trials. Not all attempts were as good as the one shown here.
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