Right now is the honeymoon phase of the Sony α7 releases, where a golden light shines over the universe and the Sony α7 can do no wrong. One of its vaunted features in the minds of its most ardent supporters is that it's a better camera body for every other lens ever made, especially Leica lenses. All you need is an adapter...
Perhaps, and then perhaps not. The first word of caution I read comes from The Online Photographer (yes, those guys) and a post made back last Wednesday titled "Two Reasons..." Give credit to Mike Johnston for publishing both sides of issue, in this case the use of Leica lenses via an adapter on the Sony α7 bodies.
The first reason in the post is a link back to Roger Cicala's article "There Is No Free Lunch, Episode 763: Lens Adapters" at LensRentals. I'd read that post already, and was glad to see it referenced in the post. If you haven't already, go read Roger's post, and pay close attention to the summary in "What Does It Mean in the Real World?" at the end of the article. It's not all gloom and doom, but it's not all sunshine and unicorns either.
The second reason was a comment that Mike elevated into that post, written by Bruno Masset. The key take-away from Bruno's comments are how Leica lenses on the Sony α7 "...hoping to use (for instance) old wide-angle rangefinder Leica lenses using mount adapters, are going to discover how mediocre the imaging performance of such lenses might be on a digital sensor." It comes down to how Sony has tuned the sensor at the corners to work with FE lenses, with a specific flange-to-sensor distance of 18mm, compared to Leica's M-mount 27.8mm distance. Leica has tuned their sensor, especially in the corners, to work with their lenses and their mount. The Leica lens and body are a system. So is the Sony α7. You purchase a Leica adapter to use your Leica lens on your new Sony body, and it won't work well because the Leica lens is now too far away from the sensor by about 10mm.
There's nothing wrong with this, and in the case of the Sony α7 it's vital to have it considering how close a 135mm sized sensor is to the exit pupil of any E mount lens. And therein lies the problem. A sensor with microlenses that are angled to make the best of the 18mm distance between flange and sensor will not work anywhere as well for lenses that are further away from the sensor, especially those on adapters and especially away from dead center.
Sure enough, over on a post by Ron Scheffler, "Sony a7 torture test with Leica, Zeiss, Voigtlander rangefinder lenses," he writes and I quote:
My take on the results: I’m hoping these lenses will fare better on the a7R. Results on the a7 are for the most part disappointing. All I can surmise at the moment is that the toppings on the a7′s sensor work against achieving optimal (or in some cases, good enough) results with the rangefinder lenses I had available for this test.I personally don't think it will be any better (but no worse) on the 7R.
This is not a slam against Sony, but a word to the wise: if you're going to buy Sony then use Sony, not just for best results, but even for good enough. I know there's a bit of pent up anger against Leica over the exorbitant price and mediocre quality of the Leica digital bodies (especially the M-9), but buying a 7 or 7R may not be the right solution. The Sony FE lens selection might be a big thin at the moment, but if you want to get the best from the Sony system, then invest in lenses specifically made for the Sony system.
Flange focal distance - http://en.wikipedia.org/wiki/Flange_focal_distance