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Single optical lens elements focal length importance of

steve001

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I was reading this thread http://laserpointerforums.com/f45/1-3-1-4watt-520nm-ndg7475-green-bullet-build-98289.html
dden bought a G7 lens to replace a G2 lens only to find out that his 520nm laser build was just barely able to accommodate this new lens, coming up almost to short in host length. What they didn't know to take into account is the focal length of this lens. Here's what he should have known. Using a single lens to collimate a diode needs to be a distance from the diode equal to a lenses focal length. Keep that in mind when building a laser or swapping for a new lens..
 
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steve001

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https://www.sanwulasers.org/product/lenses
I don't see that information on the product page. The G7 is the only example of this issue. Every other lens available works within expectations. Perhaps I'm missing the thread worthy message you had in mind.
If you had known the focal length of this G7 lens you would have known its focal length would just barely work with the length of your host and perhaps shopped around. The reason all other lenses have worked is do to them having a shorter focal length. The G2 as I recall has a focal length of around 4mm. To collimate with a G2 lens that lens would have to be 4mm from the diode. Measure the focal of the G7 lens. Something I've noticed among most the the builders here is a severe lack of the importance optics play in the final product. Without optics to produce that thin beam what you have is an over engineered flashlight.

The G series of lenses are aspherics and are known in the optic industry as Best Form lenses.
 
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paul1598419

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Actually, the FL of the G-2 is closer to 2.5 mm, IIRC. And the G-7 has a FL of 7 mm, which if placed at either end of the housing makes it almost at the end of the module to collimate the beam. Just a poor design.
 

dden4012

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While I agree with both of you and recognize I'm rather ignorant to the depth of optics I feel the OP has taken my posts from the other thread out of context in this thread. I wasn't the OP for that thread. Wasn't my build. But I did take time out of my day to present information and my experience regarding GSS's post.
The diode modules we all use for builds has been designed around the other available and required parts. The depth of the threaded lens well wasn't just a random guess that happened to work for the various lenses and variable diode can heights. So why would someone design a lens that's threaded to work with this platform, expressly intended to be used with non Sanwu lasers for this hobby market...,and place this engineered lens in the position they did. Knowing the FL, knowing the module specs...I don't have an answer for this. If the 7mm barrel would thread properly into the standard model we wouldn't be talking about this again.
 

paul1598419

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Not the G-2, but the G-7 in the end of a 9 mm to 11 mm housing. It makes infinity focus at a few turns into the module and, thus, all the slop people complain about. It would have been better to put the lens inside the housing where it would be 7 mm away from the diode when the housing is mostly screed all the way into the module.
 

steve001

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While I agree with both of you and recognize I'm rather ignorant to the depth of optics I feel the OP has taken my posts from the other thread out of context in this thread. I wasn't the OP for that thread. Wasn't my build. But I did take time out of my day to present information and my experience regarding GSS's post.
The diode modules we all use for builds has been designed around the other available and required parts. The depth of the threaded lens well wasn't just a random guess that happened to work for the various lenses and variable diode can heights. So why would someone design a lens that's threaded to work with this platform, expressly intended to be used with non Sanwu lasers for this hobby market...,and place this engineered lens in the position they did. Knowing the FL, knowing the module specs...I don't have an answer for this. If the 7mm barrel would thread properly into the standard model we wouldn't be talking about this again.
My apologies for my confusion.
Perhaps on any future builds if the threading is unknown send the part to a machinist member that can measure the threading.
 

dden4012

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No worries Steve. I had Badboybilly stop his forklift mid shift cause I got confused about the what diode was what thread and everyone was losing their mind over cyan.
But back to these G7's. I think it was Bowtieguy that said to run the 7mm version through a die to clean up and revise thread form. Or new modules that are a few mm deeper in the lens well. But they wouldn't work well or at 'll with G2 lenses. Seems like the lesser commitment would be to run them through a die.
I've also observed that Sanwu G2s and G7s lens are slightly off plane to the barrel sending the beam output out at a slight angle. Not something I see with multi element lenses. Is this due to an influence from the second or third element lens? I'm making the case that if a diode were to be pressed into module and it wasn't perfectly perpendicular to the centerline length of the module that a single element lens would reveal while a multi element lens would somehow correct?
 







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