Nikon D vs DX lens

[archisext]

Guys/Gals,

was going thru my brother's stash of camera parts yesterday and came across a sigma 28-80 D macro lens. cleaned it up and tried hooking it up to my D80. In Autofocus mode i can hear the lens trying to focus, but it doesn't seem to be doing anything.
while trying to manually focus it, it offers alot of resistance compared to when its off the camera body. why??????
tried surfing the web for some info as to why this happens. Is it because its a D lens? or its just backward compatibility issues coz it's a third party lens? or maybe the lens has seen better days.
Help! its really bugging me.

 

[ExplorerZ]

both D and DX got nothing to do with focusing.

 

[ziploc]

When trying to manual focus a AFD (or compatible) lens, remember to switch your camera to manual focus mode. The switch is to the right of the lens on the camera body with marking of M,S,C with the lens facing you. Just switch that to M. Otherwise you're forcing the AF motor to turn, and might damage it if done excessively.

 

[Squid]

"D" refers to AF-D lens from Nikon which transmits distance information to the camera for focusing.

"DX" refers to DX lens which is not suitable for full-frame SLR or DSLR. They are considered as "cropped" lens sutiable for Nikon's cropped DSLR camera.

Interpretation of "D" and "DX" can be obtained from Nikon Imaging web page.

 

[longkangman]

Guys/Gals,

tried surfing the web for some info as to why this happens. Is it because its a D lens? or its just backward compatibility issues coz it's a third party lens? or maybe the lens has seen better days.
Help! its really bugging me.

You may have to send in for re-chip or firmware upgrade.

 

[hirowen]

both D and DX got nothing to do with focusing.

I second that.

 

[archisext]

oh ok. so it might just be a compatibility problem then? or just a broken lens then. will try calling sigma to see how much it cost to fix.
thanks for the help guys.
much appreciated.

 

[jmmtn4aj]

both D and DX got nothing to do with focusing.

Well, besides that all DX lenses have internal motors whereas only some full frame ones do