Drivers, especially those pulling trailers and driving motor homes and vans, should know the limitations of the conventional mounted windshield mirror. Additional mirrors, to the sides and back of large vehicles, increase visibility and reduce ``blind spots.''
Mounting a convex lens on the inside of the rear window of a van or motor home cuts down on the ``blind spot'' immediately behind the vehicle. Use this lens when backing up or when driving in traffic to spot smaller cars which are following too closely behind.
You can also observe a car's actions if it's getting ready to pass your vehicle.
The disadvantage, however, is that a convex lens greatly distorts the distance of the approaching cars from behind. A car which is only a few feet behind you seems several times that distance when viewed through a convex lens. You can quickly correct this distance distortion by viewing the same car in normal perspective through the remaining portion of the rear window.
Motor homes, vans, and station wagons must have clear interior visibility to the rear window. A driver can easily use the convex lens by sighting through the mounted rearview windshield mirror. Make sure to mount the convex lens on the rear vertical window so that it is in line with the front windshield mirror.
You can always increase rear visibility by simply turning and looking through the convex lens. Then, too, passengers can report any obstructions behind the vehicle.
The ordinary flat-glass side mirror gives only a straight line of vision along the sides of the vehicle. The side-mounted convex mirror allows greater angular visibility to the sides. In highway travel, the flat mirror lets the driver see only one lane of traffic to the sides. The convex mirror, however, reflects vehicles which are adjacent to your own vehicle, a feat which the flat mirror cannot do.
In addition, the right-side convex mirror gives views of merging cars from expressway entrances and shows continuously the position of passed vehicles in relation to your own car.
A good practice when towing trailers is to combine convex with flat mirrors. Attach small stick-on convex mirrors to the flat glass in your standard mirror or to the bracket which holds the mirror to your car. Just be aware of the attached convex lens when making a traffic decision.
As to cost, convex lenses that stick onto a conventional mirror range in size from 3 to 5 inches in diameter and cost as much as $8. Larger convex mirrors, 5-by-7, 6- by-9, and with an 8-inch diameter, cost from $20 apiece to as much as $40 with side mounts and brackets.