The subject is a ISO 12233 resolution test chart printed out with a 600x600 dpi laser printer scaled down to fit 8.5x11 paper. Due to the varying focal lengths, the tripod will be repositioned for each lens, in an attempt to achieve a similar resulting image.

My goal here isn't to find out what the absolute resolution is, but to rather provide some baseline as to how the FA 50mm stacks up against a new DA lens and an old M42 lens of similar aperture and focal length. Output images are 1500x1500 crops with four 300x300 corner crops super-imposed to the final image corners. A perfectly parallel image subject was not achieved, so keep that in mind when viewing the corner crops as they could show more flat field error than the center.

Aperture, shutter speed, and ISO test specifics:

• F1.4, 1/20th second, ISO 100 (FA 50mm, Mamiya 55mm)
• F2.8, 1/6th second, ISO 100 (FA 50mm, DA 40mm LTD, Mamiya 55mm)
• F5.6, 0.6 seconds, ISO 100 (FA 50mm, DA 40mm LTD, Mamiya 55mm)
• F16, 5 seconds, ISO 100 (FA 50mm, DA 40mm LTD, Mamiya 55mm)

The camera body that will be used is a K10D. The lenses are a Pentax smc FA 50mm F1.4, a Pentax DA 40mm F2.8 Limited and a Mamiya/Sekor 55mm Auto F1.4 M42 mount with a K-mount conversion ring.

The shutter speed and ISO will be fixed values for each aperture setting. All images will be shot in DNG RAW mode and the resulting files will be exported in Photoshop CS2 using defaults in camera raw.

Testing Results

Let's analyze the output starting from the widest aperture samples and moving smaller from there.

At F1.4 the Mamiya 55mm lens has an edge on the FA 50 in corner sharpness, but the FA 50mm is considerably sharper in the center of the frame.

Moving to F2.8 we now have the three lenses available to look at. Right off the bat at F2.8 the DA 40mm Limited starts kicking photons and taking names with high overall contrast and sharpness and low chromatic aberrations. The FA 50mm seems to be sharpest in the center of the frame out of all three at F2.8, whereas the DA 40mm and Mamiya are pretty close in corner sharpness (lower left). The FA 50mm is still struggling with aberrations and lack of sharpness in the corners.

At F5.6 the FA 50mm made a vast improvement in overall image quality. The Mamiya is starting to show its age compared to these newer designs as it now looking to be 3rd place in overall quality. The DA 40mm takes the victory at F5.6 in all aspects, but the FA 50mm isn't a slouch either.

At F16, overall quality is equalizing among the lenses as the DA 40mm starts producing more aberrations and the Mamiya stays strong in everything but contrast. I find that the FA 50mm takes the lead in that round as it has the least border aberrations.