Do not believe about the horrors of the front-back focus! At the minimum focusing distance, the depth of field at f / 1.4 is very small, taking into account shutter speed, shutter speed, focus type, subject dynamics, etc. ! But the manufacturers of equipment, of course, also contributed - the accuracy of determining the distance to the subject is directly proportional to the cost of the carcass! Of course, the D5 will hit the target more accurately than the D3100). ! Try to give more light, use an external flash if possible, increase the shutter speed, it is possible to change the look and speed of focusing on the carcass - go for it! Do not blame everything on the lens)
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