Hello all, I need a SLR telephoto zoom lens for shooting very clear pictures of adults in daylight at 60-85 yards. I need the images to be clear enough to clearly make out someone's face to the point where you could recognize it if you knew the person (not like nose-hairs close but recognizably close). They will be still images or very slow moving so I can have a slower shutter speed and smaller aperture. I don't need a specific brand recommendation, just the upper range of the focal length. I guess my question is will a 200-400mm lens be sufficient or do I need to step up to a bird-photographing lens at 600+? I'm an amateur but I know enough to use a tripod at those distances to avoid blurring but is there anything else I should be aware of in shooting at that distance? Since daylight will be the light source and the objects mostly stationary, I'm guessing f3.5 - f5.6 will be ok for max aperture?