The Sony A7R has only been in testor's hands a few short weeks, but nearly everyone praises it for excellent resolution and dynamic range, comparable to the Nikon 800e. This is not a surprise as the A7R uses the same 36 mp sensor without an anti-aliasing filter as does the Nikon. It is a mirrorless, full frame design, so has a very short registration distance; from the rear lens element to the sensor, and thus has the space to take an adapter that fits between a Canon EF lens and the Sony camera body. Nikons and other non-Canon bodies use a longer registration distance so you cannot fit a Canon lens on a Nikon body. For Canon owners happy with their Canon glass, but wanting the advantages of increased dynamic range and higher resolution of the 36 mp sensor, there has been a flurry of consideration of the Sony A7R adapted to EF mount leses.
There are several very long threads on Fred Miranda forum, among others, that discuss this possibility. I summarize the first listed above, as of Dec 19. Also there are several even longer threads for adapting other lenses to this camera on the Miranda Alternative Lenses forum.
1. Generally speaking, it works and one can realize improved resolution and increased dynamic range over any Canon body, especially at the center of the image. However there are caveats:
2. Lens adapters in general (use of non native lenses) can introduce mis-alignments
In fact, it would appear based upon Roger's measurements that the lens adapter that doesn't introduce some misalignment is rare, although the impact, say of softer corners or asymmetrical softness, may not be noticed at all in actual use. For those looking for SOTA sharpness this is an all too frequently an issue seen by users. Typically the issue is comparing the identical high quality Canon mount lens on a 5DIII Vs an A7R. A typical result is that at the image center a substantial improvement is seen due to the higher resolution and dynamic range of the Sony sensor. But at the image edge/corner, that resolution improvement with the A7R is no longer seen and may even be worse. By purchasing additional units for test Fred Miranda is trying to deduce if this performance drop off is a sample to sample misalignment of bodies, adapters or lenses. It may not be any of these but a limitation in the micro-lens design of the Sony sensor. This may take several months to sort out.
3. These alignment issues are much more frequent in Wide Angle lenses, and full shifting with a WA Canon TSE design can also generate mechanical vignetting, not to mention problems with distortions, reduced contrast and softening in the corners, with or without extreme lens shifts. However this is not a universally reported IQ limitation. One user has found that adding non reflective material to the inside of the metabones adapter can minimize the loss of contrast due to internal reflections within the adapter.
4. There are only a few adapters that will allow full communication between the adapted Canon lens and Sony A7R body. The Metabones version III seems to work best. Even then, the AF is quite slow compared to a Canon 5DIII, say. This combination of A7R and EF lens is not for sports or wildlife shooters who track moving subjects.
5. Like all modern Canon dSLRs, the Sony A7 has the capability of electronic first curtain shutter, but the Sony A7R does not have this capability. For WA or normal focal lengths, this is probably not an issue but for those using telephoto lenses the lack of electronic first curtain will result is a small loss of sharpness due to vibration when the shutter speed is slow (perhaps 1/125-1/10 depending upon focal length). IS is not a cure all, and some users have reported IS as making the problems worse.
6. The Sony A7R captures a compressed, lossy RAW file. Some photographers have at least a potential issue with this format, but its impossible to know how much better a lossless RAW might be.
7. Physically most photographers seem to love the much smaller size of the mirrorless Sony bodies. It makes for potentially a much lighter, more compact kit. However the downside it that a bulky EF lens on an adapter can make tripod mounting of the adapted combination rather awkward. For example extra standoff clearance is needed for large diameter lenses and to allow lens movement clearance for lens shifting & rotating WA TSE designs.
So far the A7R/EF lens experiment is working, but the combination certainly will not please all shooters, particularly those who depend a lot upon AF. In fact the combination comes with a host of unique work-arounds, but the added dynamic range and resolution performance may be well worth it for some. At least we Canon owners hope that the adapted Sonys will induce Canon to introduce a high pixel body much sooner than it might otherwise.