Recently I started using a Voigtländer Ultra Wide Heliar 12mm/5.6 on my Sony NEX-7. In two other articles I already described how to configure your NEX-7 for maximum assistance with manual lenses, how to attach the lens to the camera and how to post-process the images to eliminate the magenta cast in the corners.
As I am aware of the fact, that any combination of lens and body has it’s maximum sharpness at a specific aperture I did a series of test images to find this maximum. My subject was the front of a building. It has a nearly flat surface and the clinker bricks contain a lot of fractal details. The camera was mounted on a tripod whose distance to the wall was approximately 15 meters (approximately 50 feet). Images were taken with self-timer to prevent any camera-shake. Focus was set at the first exposure which was taken at f=5.6. The image quality was set to RAW (6,000 pixel * 4,000 pixel).
While post-processing the images I did the following:
- conversion from ARW- to DNG-format
(Adobe DNG Converter 184.108.40.2061)
- correction of magenta cast in the corners and vignetting with cornerfix
- correction of chromatic aberration in Adobe Camera Raw
(ChromaticAberrationR = -15, ChromaticAberrationB = +8)
- correction of distortion in Adobe Camera Raw
(LensManualDistortionAmount = +3, PerspectiveScale = 101)
- input sharpening in Adobe Camera Raw
(Sharpn. = 25, Shrp.Radius = +1.0, Shrp.Detail = 25, Shrp.EdgeMasking = 0)
- noise reduction in Adobe Camera Raw
(LuminanceSmoothing = 0, Col.NoiseReduction = 25, Col.NoiseRed.Detail = 50)
The following image (at f=8) was scaled to 1,500 pixel * 1,000 pixel, sharpened and saved for web with a quality-setting of 60%.
For each of the marked locations in the full image I extracted a square (250 pixel * 250 pixel) which I will present at it’s original resolution. These images are not sharpened except for the same input sharpening with the raw converter. They are saved for web with a quality-setting of 60%.
In my opinion it’s easy to see that the Voigtländer Ultra Wide Heliar 12mm/5.6 reaches it’s maximum sharpness at an aperture around 8 on a Sony NEX-7. If you stop further down diffraction starts to limit the resolution. For further reading on this issue try to start at this page at diglloyd.com.