That may be dust on the prism inside of the adapter. We have a dust trap built in so this is what you need to do.

1) Remove your 35mm
2) Loosen the set screws that hold the front tube on the adapter
3) Remove the front tube exposing the ground glass element
4) Use compressed air (we recommend the Rocket Air Blaster) and gently blow both sides of the ground glass being careful not to touch or disturb the black plastic holder suspending it on the posts. NOTE: If using a can of compressed air, be very, very careful not to spray any of the compression fluid out by turning the can updside down while spraying. This can create a hard to clean mess.
5) Direct some compressed air beneath the ground glass element around the perimeter of the condenser lens (glass lens located directly behind the ground glass)
6) Blow air into the edges all the way around the condenser lens. This will force the dust inside the adapter into the dust trap.
7) Look through the adapter and see if the dust has cleared from the view.
8) If it all looks good, carefully re-assemble and you will be good to go.