After spending an hour with the 45mm on the Pentax 645D and capturing a variety of images, I headed back to the computer to evaluate the results. I’ve spent a over a week in denial. I’ve read online at the disappointing results of the manual focus version of this lens and somehow hoped the autofocus version wouldn’t be in the same boat. Not so.
Back to the brick wall…
Bear with me on these as there is a practical example at the end. For some users, the same soft detail in the corners issue that plagues the the 55mm may not be a characteristic that bothers them. When a client points out that the image is soft during a shoot, that is a huge problem in my books. 100% crops processed with sharpening but no lens corrections are below with f/stop noted underneath. The corner crops are shown from the lower left hand corner, however all four corners showed the same effect.
smc Pentax-FA 645 45mm f/2.8 lens on Pentax 645D – overall view
Center crop @ f/2.8 – soft, lacks in contrast
Center crop @ f/8 – improved sharpness and contrast
Center crop @ f/16 – sharpness is similar to f/8, little degradation from diffraction
Lower left hand corner @ f/2.8 – completely unusable (vignetting as expected)
Lower left hand corner @ f/8 – sharpness is improved, but doesn’t compare to the center
Lower left hand corner @ f/16 – still not delivering the detail of a 40MP sensor
Granted a photographer is not going to be making money shooting brick walls. As a more practical example, how does this affect image quality when shooting the front of a building? The excellent “Tapenade” restaurant in Steveston provides an example.
Positioned square to the building, this is the view of the south side.
Taking a center crop just to the left of the sidewalk and entrance shows good contrast and sharpness at f/9.
Sliding over to the left side of the image is another story. I’ve used Lightroom 3.3 to process the DNG files. Lens corrections were shut off to show a “truer” version of the results from this lens. I’m not averse to using technology wherever possible, so a version of the left side image will be shown with lens corrections turned on, too.
The grass and hedge are becoming a green blob without the detail shown in the center crop. There is also lateral (or transverse) chromatic aberration visible in the shutters. Turning on the lens correction feature in Lightroom 3.3 / Camera Raw 6.3 resolves this issue. Unfortunately it doesn’t improve the sharpenss.
While small JPEG crops don’t really cut it to show the issues being discussed here, the effects are certainly visible. Should you have sufficient bandwidth and want to see the original DNG files, they are available for download from the links below. Each files is nearly 70MB in size.
The Pentax 645D is a very capable medium format digital camera. The larger sensor compared to the 35mm full-frame cameras and lack of an anti-aliasing filter gives the camera an edge when high quality glass is used. Lens choice is key with this camera and the 645D owner needs to closely evaluate not only what is sufficient for their requirements, but how their particular lens performs as manufacturing tolerances come into play. Also, with so many used 645 lenses on the market, you don’t always know the history of the second-hand lens you’re putting on your camera.