ask the labs
Stress Less, Shoot Better
Karlen McLean, ABOC, NCLC
Eliminating lens stress makes for better lens durability and performance, and knowing what to recommend for photographers helps hobbyists and professionals get the most out of their eyewear.
ELIMINATE STRESS
Q What lens materials and techniques are best when trying to help avoid stress fractures when fabricating and mounting drilled and grooved rimless lenses?
A Polycarbonate, 1.60, 1.67, and Trivex are all good lens material choices for fabricating rimless.
For drilled rimless, the key to avoiding stress fractures is to ensure that the drill bit is clean and sharp, the pressure and speed are proper for the material being drilled, the holes are drilled to the proper size for mounting type, and you must bevel the edge of the drill holes. Failure to bevel the drill holes is the surest way to create fractures.
Poly is our material of choice for drilled rimless and can be manufactured with minimal stress when done properly.
For grooved rimless, ensure that the blade is sharp and clean and that the sizing is correct. Be aware that very light tension on the monofilament line can create stress fractures in materials such as poly, and warpage in other materials.
— Michael C. Vitale, director, corporate quality, Essilor of America, Inc., Dallas
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The Clear Picture Q What type of lenses would you recommend for this presbyopic photographer: OD) −6.25 +0.75 × 170; OS) −7.00 +0.50 × 20, with an add of +2.00 OU? A Certainly the patient needs good near vision and distance vision, so AR is in order, and I'd use a material with as low an Abbe value as is practical for the frame that's selected. Presbyopes need their add for most viewfinders, so either a high seg or short corridor PAL should be considered. Additional information is needed: 1. The patient should bring in his camera/cameras so the visual demands can be assessed; 2. Ask if the patient is using external light meters, enlargers, and/or a light tube for sorting; 3. The patient should demonstrate how he's sighting through the viewfinders, and that should be taken into consideration in the lens design, especially if this is a professional photographer or skilled amateur. — Ron Cooke, Jr., chief executive officer, Diversified Ophthalmics, Inc., Cincinnati |
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. An archive of past Ask the Labs columns can be found on the Eyecare Business website at www.eyecarebusiness.com.
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