Plano Sunwear Aberrations

[AEOC]

I had a friend tell me a "trick" where I hold up a sunglass in front of my chart projector and see if the letters get fuzzy to tell the quality of a sunglass lens. Lo and behold, we found some fairly significant differences between different lines in our office. Is this a valid test or just gimmick? BTW, the person who told me this was not trying to sell me eyewear.

[chip anderson]

Yes, valid test. Same can also be detected just holding lens at arms length and
viewing lens with motion. Waves will be seen on inferior quality lenses.

Chip

[drk]

No! Invalid test!

Put an optically-ground +/- 0.12D trial lens from the Dr.'s office in front of the projector and notice the same effect!

You routinely pass lenses with a +/-0.12D variance in ophthalmic!
That test is way too sensitive. High sensitivity but low predictive power as to whether the lenses are acceptable to wear. And I would posit that even within a lens brand there would be variation, due to manufacture, so you'd have to "test" and reject an awful lot of lenses, and all to no avail.

Don't misunderstand that I think all optics are alike, I just don't like the test you describe.

The better test would be to put the lens on a lensometer and look at the mires, the power, and move the lens around to analyze different sections of the lens. (And prism, with wrapped lenses.)

Maybe it makes sense to sample lower-quality sunlenses.

[Darryl Meister]

Here is another post discussing some of the issues involved:

Another post on plano lens aberrations

Best regards,
Darryl

[AEOC]

I talked to a quality control engineer from one of the lines that didn't do very well on this "test" and he said that the aperture on the projector is much larger (relative to pupil size) and that pantoscopic tilt and face-form wrap need to be considered. A mediocre explanation at best, especially since he conceded that he didn't have an explanation as to why some lenses don't cause the image to blur. Is it just coincidence that there is very little variation within one line of eyewear but great variation between different lines?

[Chris Ryser]

You habe drug stores and fleamarkets sell el cheapo sunglasses.

All you need is a a convincing example to your customers that they should invest in a good quality pair of sunglasses.

Chip posted a good example. I would just say ......................look at the door frame looking through the lens...........move it in a circular way and if the door frame starts moving around you get distortion and might get headeaches from these glasses.

Usually works.................customer buy's quality plano sunglasses..........no large need for scientific explanations.

[Darryl Meister]

A projector might work for finding gross aberrations, such as waves and inclusions, but it is not a very accurate means of determining "blur" as perceived by the actual wearer -- for the reasons the engineer gave you. Consequently, you might be able to surmise some indication of the "quality" of the manufacturing process or materials using this test, but you will not know really know how well the lens performs optically -- particularly for wrapped or exotic styles.

Best regards,
Darryl

[AEOC]

Usually works.................customer buy's quality plano sunglasses..........no large need for scientific explanations.

I agree. The explanations are more for my and my staff's education. As professionals, it is our ethical responsibility to understand why we recommend what we do, and not just be marketing parrots for our suppliers. Thanks for everyone's scientific and experienced insight.