smc Pentax-FA 645 45-85mm f/4.5 lens performance

In the quest for a lens with a focal length that would be considered close to normal, I tried the following two lenses:

  • smc PENTAX-DFA 645 55mm F2.8 AL SDM AW [IF]
  • smc PENTAX-FA 645 45mm F2.8

The first is the lens that was originally released with the Pentax 645D camera. While the image sharpness was fine at the centre, the soft edges were not acceptable for the type of work I do. Same comments are true for the 45mm lens. I returned both and purchased a 45-85mm zoom to see what it can do.

In my blog post on the 45mm fixed lens, I photographed a brick wall to see how the centre versus corner sharpness compared. The same wall is featured below with the 45-85mm set to 45mm and an aperture of f/8. Due to the closer camera to subject distance of the asphalt in the lower corners, I’ve chosen a crop slightly up from the bottom of the frame.

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 - overall view

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 – overall view

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 - top left corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 – top left corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 - top right corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 – top right corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 - bottom right corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 – bottom right corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 - bottom left corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 – bottom left corner

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 - bottom left corner with chromatic aberration adjustment enabled

Pentax-FA 645 45-85mm f/4.5 lens shot at 45mm f/8 – bottom left corner with chromatic aberration adjustment enabled

The crops from this image demonstrate the superior performance of the 45-85mm zoom compared to the 45mm f/2.8 fixed lens. The centre and corners, except for the top right, are consistently sharp and exhibit good detail. Focus was set to Auto as it is generally more reliable than my eye. Camera was on a tripod and ISO was at 200.

The second last image in the series shows the chromatic aberration that can show up with this lens when it is shot at 45mm. Turning on the correction in Adobe Lightroom (same as Adobe Camera Raw) eliminates the colour fringing very effectively. The lens exhibits barrel distortion which can also be removed by enabling the lens corrections.

I was very impressed with the performance of this lens at the wide end of the zoom range. In the more than three years that have elapsed since shooting this test and creating this post, I have shot with this lens extensively. Focusing manually is challenging with the slow maximum aperture, however I have found using autofocus is mostly reliable and any shortcomings in image sharpness have usually been related to insufficient depth of field or not choosing a focus point that maximizes the available depth of field.