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Thread: How to tell a glass from a plastic lens

  1. #1
    Flashaholic* AFAustin's Avatar
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    Default How to tell a glass from a plastic lens

    I know this is probably a ridiculously simple question, but I've never let that stop me. What is the easiest way to tell if a lens is glass vs. plastic? I have a couple of lights where it is difficult for me to know for sure. I remember a post from long ago that mentioned an easy way to tell---something about holding the lens at a certain angle---but I can't find it now.

    Thanks for any answers.
    Last edited by AFAustin; 09-20-2006 at 08:22 AM.
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  2. #2

    Default Re: How to tell a glass from a plastic lens

    When you look at the glass from the side it will have a green tint to it. (That's IF it is glass) A plastic lens will have a clear, whitish appearance.

    Another way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.

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    Flashaholic* Planterz's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Hit it with a hammer and see if it breaks.

    Or do the teeth thing. That's what I do.

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    Flashaholic* bitslammer's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Quote Originally Posted by xiaowenzu
    Another way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.
    Whew! So I'm not alone on this one.


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    Flashaholic* chevrofreak's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Quote Originally Posted by xiaowenzu
    When you look at the glass from the side it will have a green tint to it. (That's IF it is glass) A plastic lens will have a clear, whitish appearance.

    Another way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.
    It will only have the green or purple tint if it is antireflective coated. One that isnt coated will be "white" as well. Plastic can be antireflective coated too, so looks aren't a reliable way of checking.

  6. #6
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    Default Re: How to tell a glass from a plastic lens

    I tap my fingernail on the lens and that clearly tells me if its glass or plastic. The glass feels alot more solid and the sound is like a soft tapping where the plastic sounds like a thumping and is alot louder. It's a big difference and theres no mistaking it.

  7. #7
    Flashaholic* greenlight's Avatar
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    Default Re: How to tell a glass from a plastic lens

    the tooth-sensor works best.

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    Flashaholic* chevrofreak's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Quote Originally Posted by BigBaller
    I tap my fingernail on the lens and that clearly tells me if its glass or plastic. The glass feels alot more solid and the sound is like a soft tapping where the plastic sounds like a thumping and is alot louder. It's a big difference and theres no mistaking it.
    That worked fairly well for me too, until I tried it on my Streamlight ProPolymer 4AA. The plastic they use in that is very hard and has an almost glass sound to it.

  9. #9
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    Default Re: How to tell a glass from a plastic lens

    You could just flick the lens, if it gives a solid pingy sound then it's glass if it's a low blop type sound it's plastic. It's like when you flick crystal glassware.

  10. #10
    Flashaholic* sORe-EyEz's Avatar
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    Default Re: How to tell a glass from a plastic lens

    i guess there r different grades of plastic / glass. i swapped the original Pelican M6 2390 plastic lense w/ another photographic quality lense. & i can really see the difference between both plastics.

    any1 popped a saphire crystal lense from a watch for your flashlight?

  11. #11
    Flashaholic* sORe-EyEz's Avatar
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    Default Re: How to tell a glass from a plastic lens

    i guess there r different grades of plastic / glass. i swapped the original Pelican M6 2390 plastic lense w/ another photographic quality lense. & i can really see the difference between both plastics. plastics is fine w/ me.

    any1 popped a saphire crystal lense from a watch for your flashlight?

  12. #12

    Default Re: How to tell a glass from a plastic lens

    Quote Originally Posted by xiaowenzu
    WAnother way of telling if it's glass, is use your teeth and 'knock' against it. If it's glass, it will make a bright, brittle sound. It's hard to describe but easy to know if you try it.
    If you do it right, it will break your tooth if it is glass and it will bounce back if it is plastic

  13. #13
    Flashaholic LED BriCK's Avatar
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    Default Re: How to tell a glass from a plastic lens

    The window-lens in front of my Thor 15MCP knock-off is supposed to be glass, but tapping it it's hard to tell. I think it MUST be glass, because plastic probably would melt!

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    Flashaholic* NutSAK's Avatar
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    Default Re: How to tell a glass from a plastic lens

    I use my fingernail first. If I can't tell, I just tap the lense with the edge of a penny. I can always tell using the penny-tap test.
    - Terry

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    Flashaholic* Cliffnopus's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Another vote for the 'tooth tap'.

    Cliff
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    Flashaholic* AFAustin's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Thanks, guys, for the tips.
    You can say any foolish thing to a dog, and the dog will give you this look that says, "My God, you're right! I never would've thought of that!" (Dave Barry)

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    Flashaholic* benchmade_boy's Avatar
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    Default Re: How to tell a glass from a plastic lens

    the tooth tap woked for my u2 and a2 but i can not tell if my 8nx is or not does inyone know?


  18. #18
    Flashaholic* Arkayne's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Before tooth tap test

    After tooth tap test


    TIP: Remove strike bezel before testing.

  19. #19
    Flashaholic* RAF_Groundcrew's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Quote Originally Posted by benchmade_boy
    the tooth tap woked for my u2 and a2 but i can not tell if my 8nx is or not does inyone know?
    I have the 8AX and the 8NX, the AX lens is definitely, and obviously glass, but the NX lens, being surrounded by plastic, doesn't sound as 'glassy' when tapped. Attempts to (gently) scratch it with a knife tip proves it is glass, at least on mine, late model I think, earlier ones may be lexan.
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    Flashaholic* benchmade_boy's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Quote Originally Posted by RAF_Groundcrew
    I have the 8AX and the 8NX, the AX lens is definitely, and obviously glass, but the NX lens, being surrounded by plastic, doesn't sound as 'glassy' when tapped. Attempts to (gently) scratch it with a knife tip proves it is glass, at least on mine, late model I think, earlier ones may be lexan.
    Thanks! I am pretty sure mine is pyrex becuase i compared tooth tap to my g2 and there is defenitly a differnce but i canot decide if i have the old 8nx or the new 8nx cuz my box was very old but my green charger light stays constant on then about an hour after that it startes blinking.

    sorry for getting so of topic


  21. #21
    Flashaholic* TORCH_BOY's Avatar
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    Default Re: How to tell a glass from a plastic lens

    The Smack test will tell

  22. #22

    Cool Re: How to tell a glass from a plastic lens

    i'd just put a match under it, and if it melts... its plastic

    -david

  23. #23
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    Default Re: How to tell a glass from a plastic lens

    Glass has a more solid feel to it and much less flex. If you have a maglite for comparison that's stock. Tap it with your finger nail on the lense and it will have a hollow/ plasticy sound to it. Then go and tap a cup that's made of glass or something. Then go around to all your lights (or whatever you're trying to figure out) and see which one it feels like more. If it doesn't sound hollow, but more of a solid sound, then chances are it's glass.
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  24. #24

    Default Re: How to tell a glass from a plastic lens

    I have found that glass will feel cooler for longer than plastic, it's harder to do this in warmer climates but if you put it in the fridge for a bit and then place your finger or tongue on it you will be able to tell the difference.
    I have found some pyrex glass to have a more plastic quality when rapped on than other more brittle glass, presumably due to the annealing process.
    If you know anyone who works with glass have them show you some glass that has not been annealed, (be careful as it wants to fly apart and will shatter easily) but it has a really "ringy" feel to it, similar to glass that has been melted in a car fire for example.
    Just my 2c
    Glennser

  25. #25
    *Flashaholic* PlayboyJoeShmoe's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Dang, the SL4AALUX is kinda tough to tell though I'm SURE it's SOME sort of plastic...

    In M*gs it's a no-brainer to tell!
    http://img32.imageshack.us/img32/2640/usflaghalfmastmdwht.gif

    PBJS



  26. #26
    Flashaholic* chevrofreak's Avatar
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    Default Re: How to tell a glass from a plastic lens

    Quote Originally Posted by PlayboyJoeShmoe
    Dang, the SL4AALUX is kinda tough to tell though I'm SURE it's SOME sort of plastic...

    In M*gs it's a no-brainer to tell!
    I too found it difficult to tell, so I used a knife and put a small scratch in it. It's plastic alright, but quite tough stuff. Still, the knife didn't have too hard of a time scratching it.

  27. #27
    Flashaholic* AlexGT's Avatar
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    Default Re: How to tell a glass from a plastic lens

    I put the window close to a light source so I can see the reflection from the surface, I then press with my finger and if the reflection gets distorted is plastic if the reflection does not its glass. Hope I made sense.

    Also might want to give it a scratch on the very edge of the glass with a needle if its plastic it will scratch, if its glass it will not.

    AlexGT

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