Q. A "Little" Help from Our Friends
My co-worker and I are responsible for operating a surfacing and finishing lab for a retail store. We want to start surfacing high-index (generally 1.55) progressive lenses. We just can't seem to get them to turn out properly.

We use a quality one-step fining pad (recirculated water) and a top-of-the-line oversized "flock" style polishing pad. We generally fine between five and six minutes. Both operations are done at a lower speed at 20 psi. We make sure our polish is clean and at the proper baum. We are having difficulty getting enough surface area of the blank clear enough to accommodate larger frame sizes. To compensate, we extend polishing (and sometimes fining times) to achieve the desired results. The problem is by that time we rarely get the finished product to the required 1.5 center thickness and if we do, we tend to have distortion, "fuzziness," or incorrect optical powers. We have had the orbits checked on our cylinder machines and they're OK.

What are we doing wrong?

A.
Because of the highly technical nature of the subject, we contacted an expert -- Jay Little. He phoned the gentleman who sent in the question. Here is what Little told him:

My first question was about the temperature of their blocking alloy. They didn't know, and when they checked, it was 150 degrees. The maximum temperature should be 125 degrees. That alone would create enormous problems, especially on high index materials, which are softer and more prone to heat damage.

I asked about the condition of the centers in their cylinder blocks. The centers need to be sharp, not rounded. They hadn't changed centers for some time, so I requested they replace all the centers. I insisted there be at least 30 minutes for cooling between blocking and generating, something they had not been doing. I asked how the curves were coming from the generator. They told me they were slightly weak. A 6.00 D curve was coming out about 5.90 D, which meant they would be fining the center of the lens first. I had them recalibrate the generator so a 6.00 would come out at 6.02 D. In this way, they would be fining edges first, much preferred for plastic lenses.

I recommended a 64 x 24 stroke for fining and 68 x 28 stroke for polishing. The stroke must also be centered on the tool. If not, the curves will be affected. Like many labs, they used a one-step fining. With high index lenses, a brief one-minute second fine on a 3-micron pad provides a better surface for polishing. I am sending them some samples of a better polish and thicker polishing pads. I also suggested that a good source for useful information is to call the vendors of the equipment or supplies they use.--Jay Little, DAC Vision

Q. UV: Fact or Fiction?
Our lab's Perkin-Elmer UV spectrophotometer has consistently indicated that any and all plastics block 100 percent of UV. This includes plastic bags, hard plastic boxes, plastic bubble wrap, and even soft plastic containers. The scientist and tech that operate the equipment are confident that this is not bad or misinterpreted data. Occasionally, this lab has been used to set/change N.I.S.T. standards. I can't find anyone in the plastics or UV filter industry that verifies this. Why?

A.
I'm sorry to tell you that your data must either be interpreted wrong, the instrument read wrong, or the instrument calibrated improperly.

In my recent book, Spectral Transmittance of Lens Materials, published by the OLA, the data for CR 39 shows 10.3% UV transmittance. For AR-coated CR 39, UV transmission is 10.7%. 1.54 high index is 1.3% and polycarbonate is 0 percent.

To avoid any possible errors from misreading or misusing spectrophotometers, five different organizations were used to produce each transmission chart in the book. These companies included Corning, Essilor, Sola, Vision-Ease and Walman Optical. If there were any slight differences, they were averaged for the published data.

Keep in mind that the material tested must be a true plano, or data will be skewed. There is concrete published data to support the contention that not all lens materials block UV. One valid way to calibrate any type of UV meter is to check a plano polycarbonate lens. It should read zero UV transmission. Calibration must also be done on a regular basis to maintain accuracy.--Dan Torgersen, Walman Optical

Q. Looking for a Job?
We are looking for a trained optician for a new eyewear dispensary in a medical clinic. Is there a source for qualified opticians who are looking for a position?

A.
The National Academy of Opticianry has established a job bank on its Web site. Opticians looking for a job usually check that source first. It's open 24 hours a day and checking out job listings is always free. Companies looking for qualified opticians can also list their openings in the Academy's job bank at no cost to them. This is a valuable industry resource and available to anyone. You can find the NAO's job bank at [archive_results]?loc=archive/archive_results.asp?loc=archive/refresh/organizations/nao.htm" target="new"> www.nao.org. Employers with positions to fill can send the details via  e-mail to info@nao.org or fax them to 301-577-3880 or call 1-800-229-4828. EB

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