Nikon’s PROSTAFF 5 Riflescope with BDC Distance Lock function has an optical system located in the first focal plane, which allows the riflescope to maintain its scale and distance proportion on a target throughout the entire zoom range. The greatest benefit of these new BDC Distance Lock-equipped riflescopes will be for those who use Nikon’s Spot On™ Ballistic Program and BDC reticles to compensate for bullet drop at extended ranges.
BDC Distance Lock Reticle
Up until now, all of Nikon’s riflescopes have been in the second focal plane, which means that as shooters zoom from the lowest magnification to the highest, the reticle appears the same size in your field-of-view but is changing size in relation to your target. For Spot On users, this has meant that the aiming points provided by the popular ballistic app have been specific to one magnification (typically the highest power).
With the new BDC Distance Lock function that keeps everything in the first focal plane, the aiming points provided by the Spot On application will be the same, regardless of what magnification the riflescope is set at. This is made possible because with a first focal plane riflescope, the reticle stays the same size in relation to your target.