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Need help with collimating lenses...

analog56x

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So i learned the hard way that my collimating lenses are made of plastic, and that crazy glue, or ca melts them... i ordered some replacement ones and they dont do what i was expecting... i was expecting to have a straight beam like i had before, but with these new lenses i get a focal point, and at any distance greater than about 6" from the lense, the beam starts to widen again... i end up with a 6" dot on the ceiling...
What am i missing here?
 

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paul1598419

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It's difficult to be sure from your photos, but it looks like you bought concave lenses. You want a plano-convex lens or an aspheric lens to collimate a laser diode.

If, however, you have a 532nm DPSS laser, then you need two lenses. The one you got and the collimating lens after.
 
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analog56x

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so these are not collimating lenses? they are flat on one side, and convex on the other... maybe i have it in backwards... ill try that... i had a REALLY close look at them... i thought they were convex on both sides...

- - Edit - -

putting the lense in convex side down makes no difference.
 
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paul1598419

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Does the part that is curved go into the lens or out? If it is curved out it is convex. If it is flat on one side it is plano- convex. If it curves into the lens it is concave.
 

analog56x

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Does the part that is curved go into the lens or out? If it is curved out it is convex. If it is flat on one side it is plano- convex. If it curves into the lens it is concave.
i dont want to risk damaging the un-ruined lenses by removing one, and for some reason i cannot find the 5 that i already removed. the replacements are flat and convex, and it makes no difference weather i put them in convex side out or flat side out...

the original ones appear to be flat on the output side and, from what i can tell, they are convex on the laser side.

- - EDIT - -

Ok, so i removed one of the lenses, and it appears quite different than the collimating lenses that i bought... its very hard to tell with the original lenses (right) but it is flat on one side, and seems to be slightly convex on the other...

is there any way i could get these to work? i messed up 5, had 2 spares, so i was only down 3, but now that i took one of the original lenses out, i am down 4. i dont know the original manufacturer of these lasers, and really would like to avoid buying 10 new lasers to fix my stupid mistake with the crazy glue...
 

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paul1598419

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What color laser is this? I need to know if it is a direct diode laser or a diode pumped solid state laser. How much did the laser cost you? If it is a grren 532nm DPSS laser it is likely cheaper to throw it way and buy a new laser. You have me thinking is is a 532nm green laser and probably either a 301 or 303. You can buy a brand new laser on eBay for $4.00 to $8.00. If it is a blue laser or a red laser that is going to be a direct diode laser and a different animal.
 

analog56x

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What color laser is this? I need to know if it is a direct diode laser or a diode pumped solid state laser. How much did the laser cost you? If it is a grren 532nm DPSS laser it is likely cheaper to throw it way and buy a new laser. You have me thinking is is a 532nm green laser and probably either a 301 or 303. You can buy a brand new laser on eBay for $4.00 to $8.00. If it is a blue laser or a red laser that is going to be a direct diode laser and a different animal.
DPSS 532nm green. i bought a blue-ish purple (forget the wavelength) one off banggood, and its completely different, and has the same focusing issues. i cant get a flat beam output from it... it has a focal point, but i can adjust it to about 6ft out. when i point it at my roof, its a 1mm dot, but outside across the yard, its about 2"...

i really need to figure this out, and be done with this project :(
 

paul1598419

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If it has a barely visible beam, it could be ac 405nm direct diode laser. Otherwise, it is likely a 445nm. To go any further I need a link to the one you bought. Find it on Banggood's site and post it here. I will see it tomorrow.
 

Alaskan

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If the curve on the replacement lens is much different from the original lens, the focal length will be different, you might not be able to get it to focus into a nice straight collimated beam at the distance the original lens was from the diode.
 

steve001

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so these are not collimating lenses? they are flat on one side, and convex on the other... maybe i have it in backwards... ill try that... i had a REALLY close look at them... i thought they were convex on both sides...

- - Edit - -

putting the lense in convex side down makes no difference.
From your description "flat on one side, and convex on the orher" you have a plano-convex lens ( [) ). Any positive lens can collimate a laser beam. The problem your are having is you have not set that lens the correct distance from the diode. That distance is equal to the focal length.
 

steve001

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If, however, you have a 532nm DPSS laser, then you need two lenses. The one you got and the collimating lens after.
Actually a single positive lens will work: it must be set a distance from the diode equal to the lens focal length. The reason why two lens might be preferable in a Galilean configuration is it does reduce the working distance the positive lens will be set from the diode.
 

analog56x

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I have tried adjusting the distance between the diode and the lense, but with the new lense, it moves the focal point from about 1" from the lense to about 6".

I might just be better off buying new lasers and starting over... im a complete noob with optics, and have no idea what to do to fix these lasers :(

I dont know how to measure the original lenses so i can buy something that is the same. And with these new lenses, i have limited length so i wouldnt be able to have something longer than about 1.25" hanging off the end of the diode body
 

steve001

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I have tried adjusting the distance between the diode and the lense, but with the new lense, it moves the focal point from about 1" from the lense to about 6".

I might just be better off buying new lasers and starting over... im a complete noob with optics, and have no idea what to do to fix these lasers :(

I dont know how to measure the original lenses so i can buy something that is the same. And with these new lenses, i have limited length so i wouldnt be able to have something longer than about 1.25" hanging off the end of the diode body
Do you have any other positive lenses around such as a magnifying lens? If you do place your laser so it cannot move and turn it on. Place the lens you have handy in the path of the beam as close to the diode as possible. Move the lens away from the diode and observe very carefully how the beam and spot changes. If you do not know how to measure the focal length of a positive lens a web search or YouTube search is something you need to do.
 
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analog56x

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The only lenses i have are these alleged collimating lenses. Ill see if i can rig something up tonight. Ive been using my custom machined laser host to test the lenses, and its difficult to adjust the focus, as i have to pull the press fit nose off it and pull the laser out, then adjust it, and put it back in haha
 

paul1598419

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Actually a single positive lens will work: it must be set a distance from the diode equal to the lens focal length. The reason why two lens might be preferable in a Galilean configuration is it does reduce the working distance the positive lens will be set from the diode.
Yes, I know that, but it seemed likely if is a 532nm it would have a diverging, negative, lens before the collimaing, positive, one. It wasn't worth the time to go into an explanation on optics.
 

steve001

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The only lenses i have are these alleged collimating lenses. Ill see if i can rig something up tonight. Ive been using my custom machined laser host to test the lenses, and its difficult to adjust the focus, as i have to pull the press fit nose off it and pull the laser out, then adjust it, and put it back in haha
If those lenses magnify they will collimate. Do they magnify?
Since "it's difficult to adjust the focus...", perhaps that's the real reason you're having trouble collimating.
 
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