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Clarification on OD

laze_doctor

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From the FAQ:
What does OD mean? OD means Optical Density. Basically, the higher the OD rating on the goggles, the less light will be allowed to pass through. OD3+ goggles are fine for lasers up to 125mWs. Further than that, you'll need goggles with progressively higher OD ratings.
Is that FAQ entry correct? If so, then the OD 2.75 goggles will be nowhere near enough for a (say) 400mW laser... right?
 
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FrothyChimp

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You are good to go on 400mW using OD 2.75. On a direct exposure the lens will pass 0.7mW

The calculation is -log(OD) so you are doing -10[sup]2.75[/sup]. The minus sign indicates it is reducing by this factor. Basically you are reducing your exposure by 562.34 times
 

chido

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That's impossible, but why would you want to use your goggles outside? ;D
 

Razako

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laze_doctor said:
Great. Thanks for that FrothyChimp... that's a somewhat unusual name, btw.

0.7mW + blink reflex = safe. Not that I anticipate *ever* having a direct exposure.


Actually come to think of it that's one hell of a reduction... say, do you know if I'll still be able to see the beam with these goggles on (outside at nighttime)?
You don't use goggles outside at night. When you are pointing up at the sky or distant objects they aren't necessary. Just be careful and don't point at shiny objects like parked cars/signs.
 

FrothyChimp

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You won't see the beam but you might see a <0.7mW beam spot. Whether you can actually see the beamspot is dependent on the reflective surface on which you are viewing the spot. The direct exposure is a class II rating which is quite low so a diffused reflection might not even be visible.
 

Razako

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laze_doctor said:
In that case, is it even worthwhile for me to get the goggles? I have no interest of doing anything which doesn't involve watching the beam. I.e. burning holds no appeal for me.

So I guess the rule I'd be following is to never use it on anything close range or anything reflective (unless it's really far away).
I suppose if you only want it for long range pointing and you never plan on using it for burning or close range experimentation you can get away with not buying goggles. You can still import goggles after the laserban so there is no hurry if you ever want them.
 

Petrovski

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With my OEM AL2 goggles which are rated OD 2+ for 532nm, I can still clearly see the spot of my 100mW rated PPL. My PPL is doing around 125mW, so I'm looking at a 1.25mW or less spot. ( -10[sup]2[/sup] = 100, 125 / 100 = 1.25) I think a 0.7mW would also still be visible, but maybe very hard too see on dark surfaces.
 
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OUR FAQ IS OK!


Hahaha. But yeah, what Frothy answered is correct. With opto's glasses you'll be more than safe.

Think about it, if you bought an RPL-400 then Justin would't send you the wrong glasses ;)
 

Petrovski

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The FAQ plays it highly on the safe side. And you don't have to trust either the FAQ or Frothy, you can do the math yourself to find out if your specific laser and goggles combination are safe. Which they are. ;)
 

FrothyChimp

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Oh yes, you MUST trust me. You must believe everything I tell you for I am the EYEWEAR NAZI!
 




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