Wide Angle Camera Lenses on the Sony a7R
The Sony a7R is a 36MP full frame(35mm film size sensor) camera, that many photo enthusiasts purchased with the intention of mounting legacy and 3rd party camera lenses on. The picture quality is outstanding with just about any camera lens, but there can be issues with wide angle lenses, so we’ll highlight that issue in this post. To be more specific, wide angle rangefinder lenses are generally the most problematic, but even some standard wide angle camera lenses don’t work well on the Sony a7R. The focal ranges where these issues really show up is typically 24mm and wider, with the 35mm and up lens range being generally acceptable, with most lenses.
The problem can manifest itself as smeared corners, and/or out-of-focus blurry areas that cover the entire sides of the picture. The smeared corner issue will typically show up both before and after the infinity focus point. The OOF(out of focus) area problem is most noticeable after infinity focus, when shooting landscape pictures in particular. The OOF lens shots may look great when shooting subjects up close, but then be unacceptable for shooting big areas, that need sharp focus across the entire plane of the picture. The center of the picture is usually very sharp, in perfect focus, but then the picture falls apart gradually, starting about a third of the way in, from each side. This post will dwell on the latter problem in particular, using legacy film camera lenses, because they are cheap and plentiful.
There are a number of examples of this OOF area problem on the internet, but it’s not always noticeable, because the picture needs to be evaluated as it comes out of the camera, unprocessed, and at full size. Our first sample picture was taken by a Kiron 28mm f2.o lens, which is a nice piece of manual focus glass. This Colorado landscape shot was taken by uhoh7, who returned his Sony a7R, and purchased the Sony a7 instead. Look at the mountain range, and how only the middle third of it is in sharp focus, while the sides of the picture are very OOF.
If your bandwidth is limited, the thumbnail pic links to a 100% cropped version, edited down to three narrow strips, that illustrates the problem clearly. The full-sized 12MB version is linked below the thumbnail:
http://www.flickr.com/photos/55299472@N07/11769495364/sizes/o/in/photostream/
Here is another example of the blurry sides problem, shot at f8 with a Sigma 24mm f2.8. This lens is no slouch, it got a 4.0 rating at photodo, tested on a crop sensor camera. The center is sharp, but the sides are very blurry at this aperture, so the picture was also shot at f11 and f16. Notice how the telephone wires on the left hand side are much cleaner by f16, but at the expense of slightly less resolution in the center. The reeds along the lake are also a good basis for comparison. *Make sure that your browser is set to display pictures at full size*:
Lens diffraction testing on the Sony a7R, using a Sigma 24mm f2.8 lens.
Not all 24mm/28mm prime lenses that are put on the Sony a7R show such a wide disparity in resolution, between the center and the sides, so you’ll have to evaluate your glass accordingly. You can find out more about when diffraction starts affecting resolution at http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm Stay tuned to this website for further landscape lens testing, with a Pentax SMC 24mm 2.8 lens, and a Canon FDn 24mm 2.8.
Dan Euritt
