One issue would be that the focusing is not being done properly to align the images coming thru both the lenses. The other issue is, if this instrument was dropped or banged against something, that might have caused the prism to shift. If so, that prism needs to be realigned to get the images to align and for you to get a sharp image. You will need to open it and realign the prism or get it done thru someone proficient in rectifying such instruments.