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Pentax SMC-FA 28-70mm f/4.0

October 23, 2010

I got a new toy in the mail yesterday.  I’d been frustrated with my other zooms.  Their optics are good, but they all end or begin around 50mm.  50mm is one of my favorite focal lengths for family photography, so it was awkward.

I decided to get a zoom that started around 28 to 35 and ended around 70 to 100.  I scanned the list at Stan’s Pentax Site and, liking the reviews of the 28-70mm f/4, bought one off for $86, including shipping.

I got to take it out yesterday and here’s what I found:

  • It gives great colors and contrast.
  • Auto-focus is fast in bright light.  (I haven’t used it yet in low light.)
  • Bokeh is good at 70mm, but a little ugly at 28mm.

28mm f/4.0 - This is what I mean by not-so-lovely bokeh.

Ike on the merry-go-round - 28mm f/4.0

70mm, f/4.0 - At 70mm, the bokeh is much nicer.

Maple leaves - 65mm f/8.0

The quality of the bokeh relates to shape of the aperture.  Ken Rockwell has a good explanation here.

Looking down the lens as I fiddle with the aperture ring, it makes perfect sense that the bokeh would be prettier at 70mm than at 28mm.  At 28mm the aperture is an octagon, at 70mm the aperture is a circle.

So, if I want portraits, I’ll zoom in.  (Really, if I want portraits, I’ll use a different lens.)  But overall, I’m very pleased with this lens.

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