Better lens?

[Cube777]

Hi LPF,

First off I need to say that I am almost a noob when it comes to optics, so bare with me. So when I built my first laser I played around with the lens (660nm AR coated 3 Element glass lens) I put it in backwards just to see what would happen. What happened totally surprised me. I got a BEAUTIFUL round dot that looked just so much cleaner than the traditional lens. Now for some pics:

Normal 3 Element glass lens focused to make a big dot

And then the flipped one:

It is sharp around the edges and looks great, the only problem is when the lens is screwed all the way out it is not focused to infinity, but when
i take the loose lens and move it with my finger outside the module, I can focus it like a normal lens. I think there is a power increase because I could burn better and focus it smaller! As for the focusing problem I think using the extended lens barrel that DTR sells on his site would work well. Do you think it would work? Please leave your opinion! :thanks: for reading!

 

[Bionic-Badger]

The thing with many "good" looking lenses versus "bad" looking lenses is that the good looking lenses only produce a nice looking dot because they're blocking out parts of the beam. For example, those Aixiz lenses that have the black plastic blocking the back of the lens have a nice round dot, but at the expense of blocking out a lot of light. Likewise those G1/G2 lenses often have bad looking dots, with wings and all that because they capture nearly all of the output from the diode with their short focal length. Even Lazeerer's long-focal-length lens for 638nm lasers "corrects" the bar shape of the output by chopping off the sides.

So what you'll probably notice with the above lens is that it has far lower power than other lenses because it's probably only focusing the center of the output from the laser diode. If you like clean spots, that's great, but it'll be at the cost of output power.

 

[Cube777]

But do you think if I use the extended lens barrel that I will be able to get the lens far enough to focus it for burning without physically taking out the lens, and still hold all the little lenses inside in the right place like in the shorter barrel? I see that DTR says that the extended barrel works with a single element lens, will I be able to get all the optics from the 3 element and fit it in the barrel safely?

 

[Bionic-Badger]

That depends on the focal length, if it's short enough. The extended barrel is mostly so that the lens can be very close to the laser diode. The extended barrel is to help you screw the lens very far down into the module near the laser diode; some modules don't even have threads deep enough to permit this.

So you'd have to experiment and see if it'll fit. Those 3-element lenses have rings and other stuff to space the lenses out too.

 

[Cube777]

I have took lenses apart previously to clean it, I know the insides. But instead of getting closer to the diode, I want to get it further away.

 

[cheech226]

i'm not really sure what your problem is. the lpc red diodes focus beautifully with any standard lens if the diode was pressed correctly into an aixiz module. you're not going to get a power increase by reversing the order of the lenses. the factory makes them as they do for a reason.

 

[Bionic-Badger]

The further away from the diode, the less light the lens captures unless the lens is big. You're not really gaining much by doing that unless you just want a round beam.

 

[Cube777]

Maybe this could make those ugly multi-mode beams more beautiful? :thinking:

 

[Bionic-Badger]

They already do, such as Lazeerer's long focal length lens for those high powered 638nm red lasers, which chops off the sides of the wide beam. The problem is that you lose a lot of power because you're chopping off some of the output. The main reason G1/G2 lenses are "high powered" is because they have very short focal lengths; so they capture almost all of the output light. It's not really the AR coating. Consequently, those G-series lenses often have ugly spots.

 

[Cube777]

Thank you for all your input guys! :thanks: You shattered my dreams!

 

[Bionic-Badger]

Yeah, I went down that road already. That's why I now know -- by heart -- the true reasons why some lenses perform the way they do.