I bought a Nikon rim fire rifle scope in 3-9x40 for 22 lr. At 50 yds or more it is fine but when I went to shoot indoors at the 50 ft range it will not focus properly. I tried with it set on 3x all the way to 9x. I can get either the crosshairs or target very clear but not both. Is this a problem with the scope or is the parallax not set right ?