I want to say a few words about the quality of these two helicoids. The workmanship leaves a lot to be desired. The 12-17mm is way too tight to focus. The 17-31mm has either sand or metal grounds inside the focusing mechanism. I can feel the grinding when turning the focusing ring. It's also not very smooth. My Vivitar 2X macro focusing helicoid is light years better. Too bad it's just not thin enough. In any case, it allows me to use the Ortal 75mm f2 lens.
How well does it work? It works, but the lens is just so heavy. I kept turning the aperture ring on the front when trying to focus, instead of the focusing ring near the mount. If you have some good glass worth putting on your camera, but without the focusing ring, this helicoid may be worth it. I know I will make good use of it as I have so many weird stuff to try it on.
Took the lens out this evening and after dropping Ryan in the music class, I walked around and took some night pictures. Too bad it was so windy and cold. My hands were practically frozen after 15 minutes without gloves. The strong wind made sharp pictures almost impossible using a flimsy and tiny tripod, but a few turned out ok. I really like this lens. Will update when I get a chance to use it more.
DVP at Night -- NEX-5 & Taylor-Hobson Ortal 75mm f2. Click to see larger.