I was trying to shoot some over/unders recently with the Canon EOS1DMKII, Seacam housing, superdome, and 15mm lens. It was an identical scenario to shots I'd done many times before with the same port on a Nikon F100 and D1X with Nikkor 16mm. But even though both Nikon and Canon fisheye lenses cover the same angle of view, they behaved differently though the port.
Using AF, the Nikon lens would pretty well lock on the subject, but the Canon lens was consistently confused by the water droplets on the dome and would lock on there. This could be for several reasons:
- Closer focus with Canon?
- Quicker AF?
- Choice of AF zones?
(Note on close focus - I just researched that aspect and found Nikkor 16mm is 9.84 inches for minimum focus, while Canon focuses as near as 8 inches. No doubt that is the primary reason it focuses on droplets on that particular dome)
For whatever reason it was a hassle. Of course I could have shifted to a single AF point and the odds are I could have targeted that on a distant subject rather than a water drop on the dome. Or I could have gone to Custom Function 4-1 and used the * button. But I found I preferred the control of manual focus. Of course I did not have a MF gear for the 15mm at the time (I do now).
I bring this up only to note the difference between the two cameras/lenses, and to note that Canon shooters may wish to consider a MF gear for the 15mm, if only for over/unders. Underwater of course this is not an issue, and the extreme depth of field of these lenses will handle most compositions.
