I bought the 2.8/15 last December with the specific intention to use it with my LEE filter system. The stock lens doesn’t allow this, because of the integrated, non-removable hood. The plan was to get the lens, play a little with it, and send it back to Zeiss for a hood removal surgery if it turns out to be a keeper.
A couple of weeks later I got the modified lens, but I noticed during the very first test that left side performance has dropped considerably. I know, the 5DS R is a merciless beast, but I also knew that the lens could perform better. So immediately contacted Zeiss about the issue.
What followed is a story of exemplary customer service. I’ve sent a few test images, and after a bit of discussion they recommended a focal flange distance adjustment to let the lens focus a little beyond the otherwise hard infinity stop.
A short technical explanation why this was a good idea: all my Zeisses have pronounced field curvature – ie. when I set the focus for the image center, sides may become soft, and when focusing for the best corner performance, the center goes out of focus. This is business as usual with the 5DS R and high performance lenses.
The 15mm Distagon’s image field is arching away from the camera on the sides, meaning that I would need to focus beyond infinity to bring the corners into focus. But the hard infinity stop did not allow this. This is something you won’t see on twenty-something megapixel cameras, but the 5DS R is more than demanding.
The lens went back to Zeiss again, and after some more discussion we agreed to stick with the original plan: adjust the focal flange distance. During which I received way more information than a usual service would ever send. Focus variation test results from their lab and such. The goal was to extract every last bit of performance possible while obeying the laws on physics and the realities of manufacturing tolerances.
With the fine-tuned lens in my hand, I was curious to find out the results.
Honestly, I’m impressed. Left side performance is better than ever. Although there’s still a bit of difference in optimal focus distances between the left and right, that’s nothing I can’t mitigate with proper depth of field selection and focus bracketing. What surprised me is that peak center performance is also higher now.
The moral of the story: when you approach a service with such a claim, they usually tell you that the lens performs “within specifications” (which is a polite way of saying that they don’t care). Been there, done that. But not Zeiss. They were keen to provide me the best possible instrument for my ultra wide angle photography – and they succeeded.
Oh, and regarding the surgery – the hoodless lens have some 6mm smaller diameter than the original. It’s a better fit in my bag now. A screw-in metal front lens cap was also included in the modification package, but I’m using a 95mm Otus lens cap instead. It’s much easier to handle, and the risk of scratching the front element is way less with a plastic lens cap.