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Thread: Enclosed vs. Open Emitter Dots and Fogging

  1. #1

    Enclosed vs. Open Emitter Dots and Fogging

    I've seen a lot of folks saying that closed emitter optics are better for preventing lens fogging than open ones, due to the sealed nitrogen-purged nature of the closed design. But, the point of the sealing/nitrogen-purging is to remove moisture from inside the optic and prevent it from entering, therefore preventing internal fogging of the optic. Internal fogging pretty much means the optic is trashed, because there's not enough airflow for the moisture to easily escape. On an open emitter design, there is no internal portion to the optic, so no internal lens fogging concerns.

    However, to my understanding the sealed designs should do nothing to prevent external lens fogging. If your glass is cold and you go to a warmer, moister environment, (or breathe directly on it) you will get external lens condensation and thus fogging. I've had no problem inducing external fogging on binoculars or scopes in cold weather just by accidentally breathing on them. Aimpoint literally instructs you to fog up the lens before wiping it with a cloth to clean it, so I don't see sealed optics as being especially anti-fog.

    I know there are other potential issues with open designs in re blocking of the emitter or water on the lens, but fogging should not be worse, right? Yet, I'm seeing that everywhere at the moment, and feel like I'm taking crazy pills. Maybe it's because the same amount of fogging is less of an issue for closed designs, because the emitter is not projecting onto a fogged lens?
    Last edited by GlockenSpiel; 08-11-2021 at 12:46 PM.

  2. #2
    Value Instiller RJ's Avatar
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    Good info in this thread, in particular this post by @SoCalDep:

    https://pistol-forum.com/showthread....=1#post1184550
    Character is doing the right thing when nobody's looking. There are too many people who think that the only thing that's right is to get by, and the only thing that's wrong is to get caught. ó J. C. Watts

  3. #3
    Old man yelling at cloud OlongJohnson's Avatar
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    If the emitter on an open-emitter design fogs, you're pretty f'ed, because there's no dot to even get to the optic lens. Can be even worse with a rain drop or other bulk water on an outdoors gun. Hence why @GJM only used closed-emitter systems for his outdoor guns.
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  4. #4
    Murder Machine, Harmless Fuzzball TCinVA's Avatar
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    This winter I ended up sliding down a hill after working out in the cold all day. My belt-carried pistol ended up scooping a shitload of ice. A simple swipe of the lens and it was usable again:

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    Of course, it being cold as all hell, as soon as I went inside both lenses fogged up...but the dot was still visible and useful:

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    You can see a more extreme example in SoCalDep's thread here: https://pistol-forum.com/showthread....point-ACRO-P-2

    The problem with open emitter optics is that if you get fogging on the emitter, you may not get a useful dot. If you get fogging on the lens that faces the emitter, you may not get a dot. And this happens in more circumstances than you might imagine. Friend of mine was shooting a winter match. He drew and exhaled and just his breath from the exhale fogged his RMR to the point where he didn't have a dot or his irons.

    On a closed emitter optic that's in good working order, the emitter and the lens the dot is projected on are protected from the environment meaning that you still see a useful aiming reference even if you can't see entirely through the optic.

    Anti-fog and other measures can be taken to help out with fogging, but the open emitter designs will always be more vulnerable to environmental issues than properly made closed emitter optics.
    3/15/2016

  5. #5
    Murder Machine, Harmless Fuzzball TCinVA's Avatar
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    An example of what I mean. Getting out of an air-conditioned truck into the hot, humid air in Virginia in August:

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    Yes, anti-fog solutions help. No, not perfectly...as you can see.

    If I dialed the brightness up to max I could see a very, very faint dot. Far from ideal.
    3/15/2016

  6. #6
    Member GearFondler's Avatar
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    Quote Originally Posted by TCinVA View Post
    An example of what I mean. Getting out of an air-conditioned truck into the hot, humid air in Virginia in August:

    Name:  foggy.jpg
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    Yes, anti-fog solutions help. No, not perfectly...as you can see.

    If I dialed the brightness up to max I could see a very, very faint dot. Far from ideal.
    Was it carried AIWB in your truck or was it exposed? I've always assumed (possibly to my detriment) that my body heat would help prevent the fogging.

  7. #7
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    Quote Originally Posted by GearFondler View Post
    Was it carried AIWB in your truck or was it exposed? I've always assumed (possibly to my detriment) that my body heat would help prevent the fogging.
    Iíve experienced this same problem in MS in the summer. I carried in a JM owb, concealed under a shirt. With the AC turned up and a 15 minute ride to the range, the SRO I was using fogged up to an unusable level. This was easily repeatable. I use a 509T now, so at least when it fogs up itís still usable.

  8. #8
    Member GearFondler's Avatar
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    Quote Originally Posted by msstate56 View Post
    Iíve experienced this same problem in MS in the summer. I carried in a JM owb, concealed under a shirt. With the AC turned up and a 15 minute ride to the range, the SRO I was using fogged up to an unusable level. This was easily repeatable. I use a 509T now, so at least when it fogs up itís still usable.
    I live in South Louisiana so I'm in the same or worse situation but I've never noticed it... But possibly because I've never looked for it. I've never gotten out of my vehicle and immediately checked so shame on me. I've also never noticed at the range but by the time I've drug everything out and set up the RMR may have had time to un-fog itself.

  9. #9
    Murder Machine, Harmless Fuzzball TCinVA's Avatar
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    Quote Originally Posted by GearFondler View Post
    Was it carried AIWB in your truck or was it exposed? I've always assumed (possibly to my detriment) that my body heat would help prevent the fogging.
    It was in a case.

    I stopped the truck, put a target backer in the stand, glued up a target, and pulled thee pistol out of the case. It fogged to uselessness as soon as it hit the outside air.
    3/15/2016

  10. #10
    Site Supporter Erick Gelhaus's Avatar
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    Generally, I prefer enclosed emitter designs - especially if carries them openly, like a duty righ.

    A couple of weeks ago, these came to me from a class at a large, metropolitan agency in AZ. 1st gen 509T with internal fogging:
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