Sean Esopenko

Infinity Focus of the Sky

June 26, 2010

My manual focusing Zeiss 35mm Distagon F2 is turning out to be a serious winner in astrophotography compared against my Canon 85mm F1.8. The reason why is because the Zeiss has a true infinity focus stop. Most auto-focus cameras allow focusing past infinity so that when the camera’s searching for focus it doesn’t harshly slam against the infinity point. This makes focusing subjects at true infinity, such as the night sky, difficult.

This time around I didn’t bring the Scotch Mount out either because I’m sorting out some issues with it. It seems as though cranking it from it’s fully lowered position gives a sort of “double exposure” instead of a smooth continuous movement. It appears to require a 1/4 turn or so before it starts moving.

Without the mount, the 35mm’s field of view was much more forgiving for a moving sky than the 85mm’s. I had to shoot at 15 second exposures with the 85mm while I shot at 30 seconds with the 35mm. Even though I took twice as many exposures with the 85mm, thus theoretically having the same exposure, the 85mm couldn’t record all the detail. I think it didn’t help that it was virtually impossible for me to properly focus the 85mm because my 5D classic doesn’t have live-view and the screen is messed up.

So in the end, in my case, the Zeiss 35mm proved the winner for astrophotography, giving even more versatility to this awesome lens.

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