Quantaray autofocus

phototwin1

I have a Quantaray 28-90mm lens that I put on a friend's Nikon D3100. The lens would not focus automatically but would focus manually. Why would the autofocus not work?

bruto

What camera did it work on? Nikon autofocus lenses use one of two systems to auto focus. The earlier ones, usually labelled either just AF or AFD, have no internal motor, but depend on a motor in the camera (informally called "screwdriver" lenses). The D3xxx and 5xxx family do not have a motor, and will auto focus only with AFS lenses that have their own motor.

To be sure, look at the mount end of the lens. If it has the slotted driver for the AF, it's not an AFS.

phototwin1

The lens in question is a Quantaray lens with a Nikon mount. The autofocus worked on a Nikon D80, but not on a Nikon D3100.

bruto

The Nikon D80 has a focus motor. It will auto focus with older AF lenses, while a D3100 will not. For AF to work, the lens itself must have a focus motor. In Nikon parlance this is AFS. Other manufacturers use other designations.

Look at the lens flange itself. Here is a link to a picture of an older style AF lens, showing the AF mechancial connection. If this is present on the lens in question, it will not auto focus on your D3100, though it will function fine in all other ways, and will do no harm.

https://i.stack.imgur.com/JHLRR.jpg