Yesterday one of the OD,S i work with showed me a test he did to see how good plano sunglasses are. He turned on the projecter and on the chart was the standard snellen chart. He then held the various glasses in front of the projector, ocular side facing the projecter. I was amazed how many of them , including big brand names that were not clear and in fact some of them were terrible, others were great, even some of the glass polarized lenses were not clear. I am not going to name any brands right now until i can get an opinion on whether or not this is a valid test.
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That's why they have drug store shades @$2.00 and Cartiers@$850.00. I have seen upper tier polarized lenses that: Had the polarization 90 degrees off, others were trash after exposure to water. Some that the lenses "shrunk" and would not stay in the frame although were quite firm when new, once even a new pair shrunk after being lost in the house for six months without exposure to sunlight or heat.
Many lines will have excellent quality frames and junk sunglasses because they find a load if **** overseas at a cheap price and think it will sell with the addittion of thier name. And we all know of lines that have an opthalmic line for $50.00+ and a department store line for $15.00 selling under the same name.
Chip -
test
Chip , happy birthday,,lest i forget, i agree with what you say in your reply, but the point i am trying to ascertain is the test test the OD is doing, a valid way of testing the lenses for clarity. If it is it might explain why some people come in on occasion and tell you, these non prescription sunglasses give me a headache.Comment
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Aberration test.
Harry:
Hold them up and look at a flourescent tube across the room. Wiggle them, if aberrations are present you should be able to detect them.
No fancy equipment required. Also works on lenses of all types including contact lenses.
ChipComment
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It is not allowed to see things distorted when you look through a good pair of plano sunglasses. The easiest way to check is to look at 2 perpendicular lines. They should remain the same.
Sorry for my english...Comment
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I would be curious about window glass in this test. Any material has a refractive index higher than air, so we would expect some effect on optics. I don't think the test is properly being made. The lenses are just held up, and may not be straight with the light source. Maybe testing a pair that is good from the patient view in this way would reveal some insight. Interesting concept though :0)Comment
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Shutterbug:
This test will show a lot (all) flaws in window glass. Anyone who ever worked in a surface room is familiar. Instruments only measure small areas, above covers the whole lens. However for those of you who must have an instrument to document everything: See: Virgil Hancock: Modern Arc.
If you want to cause problems for a surface lab, just start inspecting everything with a Modern Arc. In fact one of the reasons a Modern Arc is no longer used for inspection, is there has never been a plastic lens that could pass a Modern Arc inspection.
Now back to plano quality: Many manufactures feel that just pressing or heat sagging a piece of plano glass/plastic will result in a meniscus lens of the optical quality the original sheet had. Others do not realize that the front curve on a plano must be longer than the posterior by 1/3 of the thickness. These are just a few of the reasons so many of them are junk.
ChipComment
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Objective: Contract testing of refractive and prismatic properties of various sunglass models purchased at retail.
This WEB page (above) on the Oakley website presents an optical testing of sunglasses under the title "Private Pilot 2004". There are three PDF format (Adobe Acrobat Reader) documents that you can link to read the full test report on Polarized, Men's Sport and Women's Sport lines. If you want to download the PDF documents, don't click on the "document icon", click on the text that says "Click here to download complete test results". (Wasn't the smartest web page designer!)
Are you reading more posts and enjoying it less? Make RadioFreeRinsel your next Internet port of call ...Comment
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I haven't given this type of test any consideration before, but it would probably be acceptable for detecting gross errors (such as surfacing aberrations). It could also be used for detecting unwanted sphere or cylinder power, but a lensometer would be better. However, I doubt that this kind of test would be terribly applicable to assessing the off-axis optical performance of a plano lens, since you are not actually assessing the lens as a human eye would. This would be more critical for steep/wrap lenses or lenses with exotic designs.
Best regards,
DarrylDarryl J. Meister, ABOMComment
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Chip - could you explain this a bit more? I had assumed that the two curves would be close to identical (depending on index). Thanks!Others do not realize that the front curve on a plano must be longer than the posterior by 1/3 of the thickness.
shutterbugComment
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Simple: Draw a straight line. Now take a compass and scribe an arc. Now move up the line any discernable distance and draw an arc of the same radius.
You will find that you have drawn a plus lens. The difference between the two circle centers represents the thickness. Now measure the distance between the two starting points on the straight line. Add 1/3 (or precisely .3375) of this to the radius of your compass. Put the point of the compass on the straight line at the starting point of your second arc, you will have described a plano (as compared to the original arc).
Simple geometry.
Chip
P.S. The shorter the arcs the more this is a factor in very long radii (as in most spectacle lenses) the effect is near negligible, with short radii (contact lenses) it makes quite pronounced difference.Comment
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Here's what I learned at OSU C.O. That test is invalid. What you're doing is placing a lens in front of a projected image. Any power in there at all will cause defocus. Any abberation in the lens at all will cause waviness. It is the "sum total" of all abberations in the lens that will show up on that test (probably even a smudge). The eye doesn't look through the sum total of the lens, just the optical axis + 4 mm or so. It will exaggerate the distortion in a lens.
Heck, just look through the stupid lenses. Do they look clear? Enough said!Comment
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I agree with drk. Unless you can improve the optics in my interocular lens, you don't impress me.
Distortion free = Glass
enouph said.Comment
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one of the old guys I work with did the same thing for me a few years back when I asked him about distortions in polycarb lenses. He grabbed several stock plano poly and CR lenses and held 'em up to the projector... sure enough the same thing happened with the poly lenses as you described above. The CR lenses were free of any distortions or aberrations.Originally posted by harry a saake
I don't know if it is "valid" as a test method, but it did show me one of the few drawbacks of polycarb to plastic.Comment
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Eye vs other tests
Quote:
Heck, just look through the stupid lenses. Do they look clear? Enough said!
I wonder, if the lens looks good according to this looking-through test, does this mean that there's nothing in it which would make one's eyes tired during a two-hour drive? In other words, long-term effects should be more sensitive to flaws. Another case would be a lens having sphere of, say, 0.3D - uniform and no aberrations. Such a lens may pass the look-through test as well as Rinselberg's imaging quality, but the wearer will feel uncomfortable with it as wearing it gets longer. Of course, a lensometer would easily pick that. So, the conclusion is clear: There's no standard for the quality of planos, and there should be one!Comment
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