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# Is Time Really A Factor?

#### Cyparagon

##### Well-known member
Well, that brings up another point. What are the chances the sun will be directly where you are looking the millisecond you open the door? If it's not directly on the fovea, you have to incorporate trigonometry, and the exposure is reduced.

So what if you exited theaters that face the sun and are stupid about where you direct your gaze? The point still stands the sun's focal point is much larger than a laser's focal point. You cannot equate 25mW of sunlight or fluorescent light with laser light.

#### justinjja

##### New member
Yes the sun would definitly focus to a much larger spot on your eye than a laser,

Sorry if this sounds stupid...
Is your avatar a ceramic capacitor on fire?

if not then what is it lol

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#### Ablaze

##### New member

Your conjecture applies to lenses that project onto a flat screen. The back of the eye is spherical, which corrects for any rays of light that may enter the eye at an oblique angle.

Additionally, even if the above was not true, your conjecture concerning trigonometry would not be relevant since it would apply equally well if the word "sun" was replaced with the word "laser".

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#### justinjja

##### New member
Ablaze, I don't think that is correct, if it was, when you look at the sun you would see a single point in the sky,
But really you see a ball not a single point like the apature of a laser.

#### Ablaze

##### New member
Well yes and no. Cyper has a valid point when he says that the sun cannot be focused into a single point. If it could we would see it as a single point in the sky since our eyes focus everything into as small a point as possible. However, cyper was also trying to claim that if you didn't look directly at the sun it would be smear to an even larger point. This second claim is untrue, due to the curvature of the back of the eye.

The sun takes up a 1/2 degree circle in our visual field. I will try to figure out how that affects things but I suspect it won't have much of an effect on the end results. By the way, a 6cm diameter iris actually takes up 28.26cm2. If I use that number and somehow account for the 1/2 degree, I think I would end up at approximately the same result.

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#### Cyparagon

##### Well-known member
However, cyper was also trying to claim that if you didn't look directly at the sun it would be smear to an even larger point.
Not what I said, sir. Check again. I said the exposure would be lower. I understand you're probably rusty on your trig and this requires some spacial thinking, so I'll spell this out as best I can.

This is why solar panels work best at right angles to the sun.

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#### BrittanyGulden

##### Guest
..you guys are losing me W/ your special functions I'm still on Calc lol

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#### BrittanyGulden

##### Guest
You won't find 150mW or higher singlemode IR diodes because at those power levels your only option is to use a multimode diode. There are no singlemode IR diodes at those power levels, hence my suggestion to use multiple singlemode diodes. You don't want multimode diodes for your application because of the uneven power distribution. Hot spots are dangerous. Using multiple single-mode diodes gives you more even power distribution. I know that you say you'll "only be illuminating your target" but even so it would be unwise for anyone to recommend a dangerous course of action.
So you are saying all Multi-Mode Dioedes are "too dangerous" to be used. -There has to be Safety Glasses for "multi-mode" diodes even if there is "hot spots" present.

#### Ablaze

##### New member
He is saying that multimode diodes may not have even distributions if you spread out the light a lot. The dot might end up looking a bit like this:

.._______
/________\
../_____\

I don't think the distinction between multi mode and single mode will matter much to you.

I'm no knight, cyper.

The back of your eye is not a flat plane like you drew in your picture. It is the inside face of a sphere. If you draw your picture with that black line being a portion of a circle that intersects with the focusing lens (like our eyes) rather then a straight line you'll find that you experience the same density of rays no matter what the angle of incidence.

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#### Cyparagon

##### Well-known member
The back of your eye is not a flat plane like you drew in your picture.
You're confusing retina with pupil. I illustrated the pupil, not the retina. (I'm pretty sure I labeled it, too).

Here. Does this explain it any better?

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#### Ablaze

##### New member
Now you're just picking nits.

Irregardless of which geometry you were referring to it still applies equally well when applied to lasers as it does when applied to the sun.

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#### Cyparagon

##### Well-known member
Now you're just picking nits.
:tired:

You said there was no trig involved. There are no nits when I prove to you there IS trig involved. :na:

THIS would be picking a few nits: "irregardless isn't a word."

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#### Cyparagon

##### Well-known member
Heh, I especially like the part where "Most dictionaries list it as 'nonstandard' or 'incorrect'." :crackup: