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Nikon 70-200/4: Torque on the Lens Mount vs 70-200/2.8

Nikon 70-200/4 VR with optional RT-1 tripod foot
Nikon 70-200/4 VR with optional RT-1 tripod foot

See my ongoing review of the Nikon 70-200mm f/4G ED VR.

Torque on the lens mount can subtly affect image sharpness by applying a tilt or swing; this is why heavy lenses have a tripod foot.

Always support heavy lenses directly; do not allow the lens mount to take the stress as it can be subtly bent (5-10 microns of skew shows up easily enough, yet is invisible to the eye).

Jack M writes:

Would you measure the center of gravity of the Nikon 70-200/4 for me? Balance the lens on your finger. Measure the distance from the rear rubber gasket to the balance point. A rough measurement estimate to the nearest tenth of an inch would be great. You might want to do this over a pillow. :-)

The calculation is a simple one. Force x moment arm = torque. The moment arm, sometimes called a lever arm, is the distance measurement that I'm requesting. I calculate torque (with the force of gravity perpendicular to the lens axis) on the camera lens mount flange for my two heaviest lens as:

Nikkor 70-200 f/2.8 VR II without both the lens hood and the mounting foot: 1.34 foot-pounds
Nikkor 14-24 f/2.8: 0.44 foot-pounds

I supplied the figure (including the hood) to Jack M and he replies:

0.30 feet x 1.87 pounds = 0.56 foot-pounds of torque for the Nikon 70-200/4.

This is less than half to torque applied by the 70-200 f/2.8 lens and certainly supports your observation about the feel of the lens on the camera. I don't know what Nikon's spec is for max torque on the lens mount flange, but at approximately 0.1 ft-lbs more applied torque than the 14-24, the 70-200 f/4 would seem to fall in the class of lenses that do not require a lens mount foot. (weight source: B&H web site)

DIGLLOYD: On the camera, it feels like a large difference in carrying the ƒ/4 versus ƒ/2.8 lens. I am comfortable with the 70-200/4 being supported by the lens mount, but the 70-200/2.8 VR II is definitely beyond the stress I would ever want to apply to my camera mounts.

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