Looking for Answers about Nikon Inc. AF-S DX NIKKOR 16-85mm f/3.5-5.6G ED VR?

The 16-85mm lens is a DX lens which means it is designed for the smaller APS-C sized image sensors of Nikon's DX series of digital SLR cameras. The D3x (along with the D3s, D3, and D700) all use a 'full-frame' 35mm sized sensor. While the lens is compatible with the camera, you will not be using the full image sensor and will end up shooting images using just a smaller portion of the sensor at a reduced resolution.

If you don't have other DX cameras you need to use this lens on, you may want to consider searching among lenses designed for full frame. A suggestion would be the 28-300mm VR lens.

This lens is for the dx format. Maybe the d3 x could use it but only half the sensor shall be used, the pictures shall have half the max. megs in the d3 x , check with your dealer.

You can use it on the 3x but in crop mode which kind of defeats the idea of having a D3x in the first place. If its wide angle you are after why not look at getting a 17-35 2.8, superb lens that it is.andwork very well o

DX lenses on FX cameras provide vignetting because they were purposely made to to fit cameras with cropped sensors.

You may also want to check out this article from Nikonusa.com:

What lenses can I use on the Nikon D5100, D5000, D3200, D3100, D3000, D60, D40X, and D40?
http://support.nikonusa.com/app/answers/detail/a_id/16436

Second part of your questions, the D5100 does not have a built in focus drive, so you need lenses with a AF-S or the older AF-I designation. They have built in focus motors. If you look up the specs for a camera it will tell you what classification of lenses are compatible but won't list them individually.

Yes, definitely.

Its perfect for that.

Very good at the wide angle end. Some distortion as expected. Is equivalent to 24mm on my D300.

Yes, I use this lens with the D5100 - its incredible sharpness really brings alot of detail to the 16Mp sensor in this camera!

Here's a great article that explains which NIKKOR lenses are compatible with which types of Nikon cameras: http://www.nikonusa.com/Learn-And-E...

yes

yes

as has been said before:
massive supply issues with all Nikon stuff since the floods last year.. :-( hoping it'l be sorted soon (question above) i'm wanting a new camera as mine has problems.

It's not only compatible, it's a great match for that camera!

Cheers,

Frank