Pentacon 50mm 1.8 on Nikon SLR compatibility?

This is a really old lens I found. It has an adapter for F-mount and I tried it on a Nikon FM-10 and it seems to work. This lens is really weird though. When you turn the aperture ring it does nothing and is always wide open. There's a button on the side of the lens that you can press down and the more you press it down the smaller the aperture gets (f1.8 to f16). The lens also seems to meter correctly. I haven't took any pictures yet just testing it without film. Do you think this lens will work even though you have to use the button to control the aperture?

Added (1). Oh and when you press it down the viewfinder get's darker so this a stop down metering lens.

Added (2). ***I just figured it out, you set the aperture you want and press hold the stop down button and take the picture. The blades will go to that aperture. Now I'm wondering if the pictures will come out right I won't know till I try.

Not all facilities of the lens will be transferred to the Nikon by that adaptor. If there's a 'manual stop down switch' (maybe M/A) on the side of the lens set that to Manual and stop the lens down like that, but the view will be dark through the lens. That's how things were in the old days! Actually it sounds as though you have found 'manual stop-down' already. All you can do now is try - probably most pics will come out fine.

The side-tab stopdown suggests this is a rebadged Meyer Oreston*, a great lense very much in demand. Later Pentacon lenses were multi-coated and had a auto/manual switch to handle the diaphragm. *The East German photo-industry like it's western counterpart, was full of people having great ideas. All the screw mount Pentacons are based on Meyer designs.