Hi, this probably is a dumb question but here goes anyway, recently I read that all f/stops or aperture settings let in the same amount of light at each stop regardless of the brand of lens or size of lens ie F8 on a nikor 105 macro lens allows the same light in as f8 on a 70 - 200mm canon lens. So here is my question my brother in law owns a Ziess 100 mm macro lens which goes from f2 to f22 and we own a nikor 105 mm and it starts at f2.8 and finishes at f40, so although at F8 both lens supposedly allow the same amount of light in IS the depth of field the same at f8 on both lens or is F8 on the Ziess equal to f16 or there abouts on the nikor or because the nikor goes to f40 does that give it an overall greater DOF.