Depth of field at a focal length of 200mm, F4.5 with a subject distance of 30 meters is 3.8 meters.
If you focus on the nearest point the you are losing 1/3 focus towards the back.
Remember also that focus works a single plane so you need to take that into account as well.
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|| Canon 20D x2 | 17-40L | 24-70L | 100 USM Macro | 100-400L IS | 580EX ||
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