ask the labs

Outdoor Performance

Karlen McLean, ABOC, NCLC

DARN SHOOTIN'

Q I've recently heard about using an inverted D-seg bifocal segment for competitive pistol shooting.

My questions are:

Is there such a thing?

How is it made?

How does it work?

A Shooters are trained to fully extend but not lock, their arms. For most people, that results in a focal length of about 20 to 24 inches at the very far end of the effective bifocal range when utilizing the site on the target.

The focal length can be greater for a handgun with a non-conceal length barrel. So, if a shooter typically wears a +2.50D add for example, they might use a +1.25 or +1.50D add here. Emerging presbyopes, say those wearing a +1.50 or lower add might be out of luck due to the lack of availability of add powers in D-segs much below +1.00D.

I checked with the senior sidearm instructor for both the Minnesota Division of Natural Resources and State Patrol. Without knowing anything about optics, she said she felt the focal range was too great for a bifocal and that most shooters with corrective lenses use the distance portion only for aiming.

That said if you thought this might be successful for a highly specialized incidence or person, you could fabricate an upside-down bifocal by generating the lenses left for right and then edging them inverted. They would have to be blocked for this intent, in order to overcome the typical nasal decentration of the segment.

— Robert Gustin, vice president, business development, Walman Optical, Minneapolis, Minn.

If you have a question you'd like to have answered in Ask the Labs, send it to Karlen McLean. Email: karlen.mclean@wolterskluwer.com. Fax: 215-643-1705. An archive of past Ask the Labs columns can be found on the Eyecare Business website at www.eyecarebusiness.com.