Hi, i want to ask that is these lenses compatible with my Sony Alpha 200 with Sony 18-70 objective.

than you

If your Sony 18-50 is 55mm diameter they should be Those lenses are screw mounted on the front of the objective.

No idea but please let us know if they are. I'm curious myself.

EDIT: I just remembered, my mother had an older 32mm film camera, Nikon D series that quit working and was too expensive to fix. The external flash that came with it works with my digital but the lens did NOT. The lens threads are the same but there's some senors on the digital 18-55 mm lens that the standard 32mm lens seems to be missing. Pity too for a spare lens would have been nice.

So I think as long as they are both digital, you might be ok but please give us an update.