Idea for ir filter mabee?

drewlrocks · Jan 17, 2009

Hello i have a 50mw dx laser and i was wondering if i were to put a black trash bag inside of the lens cap about 1.5cm away from the lens would it act as an ir filter because the ir spreads out and the trash bag would get a very tiny hole the size of the laser wavelength in it thus blocking the ir accept in the beam correct me if im wrong.

Southpaw · Jan 17, 2009

i believe that the IR escapes along with the green so once it burns through the hole both of them are getting through. This might eliminate the radial effects, but im not too sure bout this :-/

drewlrocks · Jan 17, 2009

yeah thats what i mean because the ir spreads out like a flashlight but my laser would only burn a hole big enough for the laser light so the ir would barely get through. for example tale a light bulb and but it up to the trash bag with the tiny hole and barely any would get through.

Southpaw · Jan 17, 2009

but even if u use that example, once the light gets through there still is the flashlight effect, just smaller because your blocking out 95% of the light. But if you block out 95% of the IR, then there goes 95% of the green as well, terrible i know

drewlrocks · Jan 17, 2009

what im saying is the flashlight effect will be blocked but the laser will be at full power because it will burn a hole as big as it needs right through the bag. correct me if im wrong.

Southpaw · Jan 17, 2009

yea, i get what ur trying to say, but if there is any IR getting through it will still do the flashlight effect but to eliminate IR either get a filter or block the green as well

\^^/
( ) <-- laser before

\^/
( [ ] ) <-- after... The laser will still expand out, just with less going out

drewlrocks · Jan 17, 2009

so what your saying is it will reduce it by a little but not much or will it help a lot like over 80%?

drewlrocks · Jan 17, 2009

How much is a ir filter?

ElektroFreak · Jan 19, 2009

Check the link in my signature. There are 12mm IR filters there for $10, or you can get them through novalasers.com for the same price. Schott BG38 absorption glass makes the best IR filtering material for green and blue lasers..

BeavRat · Jan 25, 2009

How would you attatch either the optotronics one or the bg38 filter to the laser? Also, where can I buy a sandstone green laser?

wummi · Jan 26, 2009

an aperture will NOT block ir, or something. the problem lies within the differnt focussing of different wavelengths! im gonna draw a quick graph to explain the problem, in a minute

kendon · Jan 26, 2009

the plastic bag idea will absolutely not work. i was about to draw something too, but now i'm waiting for wummis version ...

is there any tutorial or something on how to mount the filter to or better inside the dx pens? i am waiting for one to arrive, and i was thinking about filtering it. but i want it to be nice, in the best case you shouldn't be able to see the modification from the outer apperance.

wummi · Jan 26, 2009

so here we go:

to understand this, you have to understand that different wavelengths refract differntly. as in IR light doesn't get bent as much as Green light, when passing through glass.

if you collimate your green laser, the emitted IR isn't collimated

it you try to put an aperture in front of your lens, the IR will still spread like a "flashlight"(exaggeration! IR divergence is just a few mRad more than your visible beam. but this is hard to draw. still, the graph illustrates the mechanism), as it still isnt collimated

even if you make your aperture the size of the green beam, it will still look something like this:

hope that explains the problem ^^

edit: whoops wrong pics. now fixed it

wummi · Jan 26, 2009

also, if you have an old/broken videocamera/webcam/photocamera, right before the sensor is an IR filter you could harvest. they block about 85%, not the best, but the cheapest if you have something old

JLSE · Jan 26, 2009

"
it you try to put an aperture in front of your lens, the IR will still spread like a flashlight, as it still isnt collimated "

Where do you guys get this idea? Without an IR filter, depending on the laser, at 20ft away you can have a 4in IR dot with a 5mm green dot. IR does NOT spread like that of a flashlight, although it seems to be a common myth around these parts.

Yes it does diverge differently than that of the green, but it wont make a 10ft dot at 20ft away like one would expect from a flashlight.

Common misconceptions should not be posted as fact. Before an answer is given, perhaps trying it first and seeing for yourself will stop such myths from travelling around as fact.

Just a thought

lasersbee · Jan 26, 2009

wannaburn said:
"
it you try to put an aperture in front of your lens, the IR will still spread like a flashlight, as it still isnt collimated "

Where do you guys get this idea? Without an IR filter, depending on the laser, at 20ft away you can have a 4in IR dot with a 5mm green dot. IR does NOT spread like that of a flashlight, although it seems to be a common myth around these parts.

Yes it does diverge differently than that of the green, but it wont make a 10ft dot at 20ft away like one would expect from a flashlight.

Common misconceptions should not be posted as fact. Before an answer is given, perhaps trying it first and seeing for yourself will stop such myths from travelling around as fact.

Just a thought

Isn't this the Science Fiction section.... :-?
I must have made a wrong turn somewhere... :-/
;D ;D ;D

Jerry

Idea for ir filter mabee?

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