When I originally joined this forum, I had exactly one lens for my D800--a Zeiss 100mm Macro-planar. I added a 15mm Distagon, 55mm Otus, a 135mm ZA, and the 35mm and 80mm G-series Nikkor lenses. With these lenses, I took a lot of photos and posted them here: pictures of moss, mushrooms, horses, street scenes, a wedding, and a lot of sports.
For all those images I was very happy with my cameras and the lenses I was using, particularly the Otus and a 35mm Leica summilux I had picked up. However, I had been curious about medium format from the beginning. My first real camera--a Yashica two and a quarter was almost medium format, and I knew my uncle used a 4x5 to shoot his paintings for his portfolio. What I'd seen on the Internet regarding Hasselblads and Pentax digital cameras though was very exciting. The prices made the cameras impossible, but still--I always wondered what they'd be like.
More recently, just when Phase One phased out their DF+ camera and the 2xx line of IQ backs, they put the other gear on sale. So I got a DF+ and an IQ250 for a reasonable price. This system uses SK leaf shutter lenses and I simply cannot mount any of my other lenses to this camera. The sensor is bigger, meaning the mount is bigger also--too big for 35mm lenses.
After buying the P1 gear, I ran a number of tests against (primarily) the Otus. My conclusion was that the Otus is better than the SK lenses because its color control is a lot better. The SK lenses have noticeable LOCA when shot a certain way but the Otus never has this problem. That said, the P1 sensor is better than the D800 or A7r sensor, so the colour rendition is better overall. As long as LOCA is controlled for by stopping down the lens and not pointing it directly at a light, the results are good.
All of this is to say that it is amazing to me that the Otus is so much better in this way than the SK lenses. I am shooting the P1 a lot more lately because it is easier to use than the D800 or A7r despite its greater bulk and weight, but I really wish Zeiss would make lenses that could fit on the P1--preferably with AF. I used the P1 for a portfolio shoot in Thailand that I posted here recently and am happy with the results, but also remember that several photos needed careful retouching to eliminate purple fringing.