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I use a Nocto (Yokohama Japan, web site in Japanese only) adapter for all my classic Contax lenses on an NEX 7. I understand that Kipon makes an adapter for the 50mm Zeiss lenses to NEX, but I think that a quality adapter is needed for a quality lens.
Tried to post the Google translate link but no go. I suggest yo search for "nocto.jp" then select a translator. On the left side of the main page you will see some thumbnails. Click on the picture of an Olympus with a Contax adapter on it. 3rd from top. On the new page scroll down to the items withno picture shown. The 6th from the top in the left column is the Contax-C to NEX adapter at 52500 Yen. It is currently out of stock, Kipon has a CRF-NEX adapter on e-bay at $185.07. A lot less than the Nocto at $600+. It ma serve your purpose. It was not available when I got the Nocto.
If it has an internal bayonet mounting and a focusing helix it will work. No need to worry about a focusing scale or depth of field scale as you're focusing thru the lens at your working f-stop. The same applies to any focus shift you may hear of (not an issue when viewing snd focusing thru the lens.
The post war 1.5 Sonnar's optimal f-stop is between f5.6 and 8. On the NEX 7 I would not stop down below f11 on any lens due to the defraction limit set by the high resolution sensor.
Again best of luck and enjoy your new adapter and Sonnar 50mm 1:1.5 on the Nex 7.
Be careful buying a less expensive adapter as many are for the outer bayonet only and will not take the 50mm lenses.
See my flickr pics as the newest is with a pre-war CZJ 5cm f1.5 Sonnar on the NEX 7. It's a little out of focus so I'll re-shoot it today.
I use NIK Software's Tonal Contrast, Contrast Only and Sharpener Only on the ARW file and then remove color noise with Photoshop. Finally I convert to a JPG and apply Versace's Midtone Contouring, flatten and save.