For all of the particulars on this lens, Ken Rockwell has an in depth review. http://www.kenrockwell.com/zeiss/slr/21mm-f28.htm.
I can tell you from personal correspondence that Ken is not a Sony fanboy.
My prime directive when backpacking in the Sierras was to keep my gear and myself as light as possible. So you might ask, “Why in the world would you buy a lens that is so big and heavy (25.4 ounces) that it could be used as a boat anchor?” With the Nikon to Sony Metabones adapter, the lens is just shy of 2 pounds. That is only one pound lighter than my tent.
One could probably wonder whether I have a camera with a lens on it or a lens with a camera on it because this prime lens is more that twice as heavy as my camera. However, if I could only have one wide-angle lens, this would be it. I researched this lens as best I could on the internet and YouTube but there are few photographs taken with this manual lens and the A7R.
I first encountered this lens as one of the Contax/Yashika lenses. It is also remains available as a Canon and Nikon mount lens. I have read enough to know that wide-angle lenses can be subject to distortions, flare and vignetting. There are also problems with using polarizing filters. I used a circular polarizing filter this morning.
I couldn't wait to try some shots this morning and started just after sunrise. While the first hour of the day offers a wonderful angle for sunlight illumination, it posed problems with my photographs that I had not anticipated and didn't notice in the electronic viewfinder. I varied the aperture from f2.8 to f22. When I downloaded the photographs, I was somewhat surprised to see corner vignetting on some of the photographs (wide open). This was easily rectified in Photoshop with the filter adjustment tool.
However, there were also problems in the sky in the center of some photographs. I think this was a function of the low sun angle and or the polarizer and or where I stood in relation to the sun.
Where were the photographs what I was looking for? Overall, I was very happy with what I saw. I had also ordered a 82mm UV filter and replaced the polarizer when I got home. Problem solved. No vignetting and no dark spots in the sky in the center. I have included some photographs with some explanations underneath.
Click On Photographs To Enlarge
Problem Created By Low Sun Angle and Circular Polarizer Filter
Problem In Right Top Lesser Degree
Noticeable Issue Here
Circular Polarizer Replaced With UV Filter
This lens has great potential as I learn more about using it with a UV filter and find the location that is best suited to the strengths of a wide angle lens. I think cloudless skies are a particular problem for a wide angle lens with a circular polarizing filter. Deep in mountain basins and passes seem like great spots for this lens. Guess I'll have to take off a couple more pounds and forget about the polarizing filter.