The 18mm Batis has a remarkable design and manages clearly better crispness in the far corners at f4 than the Heliar at f11, but the thing you may not have thought of is this: depth of field. As generous as this is at 18mm, think again at what is in those corners with an 18mm lens. The top corners are likely to have either sky, foliage or buildings that is considerably further away than the grass/rocks/tarmac close to your feet in the bottom corners. In many cases, the subject matter in the bottom corners is 1m away, plus or minus. This means f4 still does not cut it for depth of field and you end up in f8-f11 territory, where the advantage of the Batis diminishes somewhat (but is still visible). Surprisingly, the Zeiss 18mm f2.8 Batis had some decentering. The top left was never quite as sharp as the other corners, but got close by f5.6. This corner was still a touch better than the corners of the Heliar, but stood out simply because the other corners were perfect. This was not something I had expected with a ‘real Zeiss’ lens and is a first for me. I’ve got four Zeiss ZM lenses (for Leica M mount) and not one shows any decentering on my Leica Monochrom. I would have thought this just a freak sample with the 18mm Batis being decentered, but experience with the 25mm Batis told me otherwise (see later).
Click below for next page!