f2.8 and f4 Comparison

Zeiss ZF 25mm f2.8 (Wide Open)

Zeiss ZF 25mm f2.8 at f2.8 (wide open). 100% crop: lower-right corner from Nikon D2X

Spot-on wide aperture performance, this: Leica-like. How gracefully this resolution is maintained into the real corners remains to be seen . . .

Performance Comparison at f4 (Centre Frame)

Nikon 24mm f2 AIS at f4 (Centre)
Zeiss ZF 25mm f2.8 at f4 (Centre)

Considering the ZF is giving away a whole stop, it’s impressive how it brings to the table all the traditional Zeiss attributes one stop down from wide open: microcontrast and, to a lesser extent, resolution, are clearly superior to the Nikon f2 at f4, rendering a much more ‘believable’ 3D image. Detailed tests of its wide open performance corner to corner will be the subject of another test, but there is reason to believe that the ZF’s wide aperture performance will be exceptional. Here’s a 100% crop from the extreme lower-right corner of an APS sized capture:

Performance Comparison at f4 (Centre Frame)

Nikon 24mm f2 AIS at f5.6 (Centre)
Zeiss ZF 25mm f2.8 at f5.6 (Centre)

Apart from the exposure, which pumps more midtone information into the Nikon shot, the primary different centre frame between these centre f5.6 crops is distortion: Zeiss has clearly paid a lot of attention to geometric distortion with their new, potentially class-leading ZF. The corner crops demonstrate that chromatic aberrations are well corrected, too.

Performance Comparison at f5.6 (APS-sensor ‘corner’)

Nikon 24mm f2 AIS at f5.6 (Corner)
Zeiss ZF 25mm f2.8 at f5.6 (Corner)

I’m not sure this ‘corner’ performance is unbeatable at this aperture: the Canon 24mm f1.4 L is exemplary at f5.6 across the frame, and the little Olympus 24mm is starting to come on song . . . however, compared with Nikon’s best at 24mm, the Zeiss ZF shines again: straight lines, no red halos and marginal resolution loss.

Performance Comparison at f8-f9.5 (Centre Frame)

Nikon 24mm f2 AIS at f8 (Centre)
Zeiss ZF 25mm f2.8 at f9.5 (Centre)

One or two point to note here: the ZF was tested at f9.5 against the Nikon’s f8. Either the f2 rates its apertures rather too optimistically, or perhaps the f2.8 is a little faster than it pretends to be . . . the lens certainly looks big enough to be an f2. Also note the typically cool colour rendition of the Zeiss: though the natural lighting in this series of shots varies somewhat, the Nikon f2 is consistently warmer.

Performance Comparison at f8-f9.5 (APS-sensor ‘corner’)

Nikon 24mm f2 AIS at f8 (Corner)
Zeiss ZF 25mm f2.8 at f9.5 (Corner)

Typically, both Nikon and Zeiss wide angles like to be stopped down to at least f8 to deliver their best; once again, though, the new ZF outstrips the ancient AIS lens by a significant margin.