Nikon D5100 shooting black photos?

I recently received an older 135mm lens for my nikon most likely dating back to the late 80s or early 90s. Its switched to manual mode and can shoot video perfectly fine. When I go to take pictures, the photos turn out completely black unless I greatly decrease the shutter speed.

Decreasing the shutter speed only gets me slightly brighter pictures. I understand this is most likely caused by some incompatibility with the lens and camera but I want to know if there's anything I can do to at least brighten the photos or change some settings around

You can't change any settings manual mode is your only option… I don't mention this much because it isn't the easiest thing to do… And to be honest it's more about me 'showing off' than anything else… For a bit of fun i'll stick a manual lens on my D5100… The lightmeter won't function so you need to guess the 'exposure'… It isn't difficult for someone that works with cameras constantly… It impresses newcomers though.

I don't recommend this to 'newbies' although it isn't a bad thing to experiment with… You could look into some of the hand held exposure/light meters and use that to get your correct exposure… They are pretty accurate.

Because your camera can't meter with the older lenses your only option is to shoot 'blind' (guess the exposure) or use a hand held meter.

Shoot in manual mode. Raise the ISO to 400, shoot at f8 and bracket shutter speed from 60 to 200. Change the aperture and bracket from f4 to f11 to see where you get the best exposure.
Older Nikon lenses usually will not engage the computer in the camera.

read up here: http://mir.com.my/rb/photography/companies/nikon/nikkoresources/135mmnikkor/index.htm