It probably may have been knocked out of place in shipping.... (like that never happens)... a SPANNER tool is what is needed to access a good grip on those nuts. those are available at a full service tool/hardware store. you want to adjust till you have an equal black area around the image. while you're at the tool/hardware store get a little ounce bottle of model car paint to apply to the nuts you adjusted to lock them down. Then with compressed air gently blow out dust a flacks of paint loose in the viewfinder.