I’m running the Deployable Laser System with the included Opt PLH3D-15W laser head and it’s been an awesome setup.
But… even with all the additional clearance it provides for 3D etching I’m finding I need more.
I’ve exhausted all physical mod options and Increasing the laser focal length is the only one left - by about 25-30mm
There’s been little word from Opt but they get the benefit of the doubt b/c they have to live with that psychopath Vlad as their neighbor…
I understand I would need a collimating lens but I suspect there might already be one in this oem module (?).
Is it possible to add an additional lens in place of the air nozzle to increase the focal distance?
Calling @jjneeb 
This is something I went through a couple years ago, mostly as a learning excercise.
The short answer is that with a longer focal length lens on that laser, you will sacrifice beam/spot width too much to make it very useful.
The long answer:
All of Opt’s laser heads have the collimating up in the laser body, and then the focus lens screws on the outside. You can see that if you unscrew the lens and then do a test fire, it will make a fairly small spot that stays close to the same size as you change your Z height on the CNC. I say close because there is no such thing as a perfectly collimated beam, so it does diverge some.
With the focusing lens, you trade off beam/spot size and effective working height with focal length. So the longer the focal length, the greater the length of the beam that is its smallest (this is great for cutting and makes the laser much less sensitive to being perfectly in focus), however, the spot size will grow in diameter as the focal length is increased. So your burns get fatter and power density rapidly decreases (PD is inversely proportional to the square of the beam diameter). This is why most CO2 lasers have options for many different focal length lenses, so you can use short ones for very fine engraving or when you need the highest power density, or longer ones where you need to cut thicker material or need to reach down into a hole or something.
I got a couple extra custom lenses for the 15W a couple years ago to experiment with. I think I had a 75mm and 150mm set in addition to the stock one (which I think is 30mm). The main thing I learned is that you can’t just add a new lens and get great performance :-). The beam was just a little too big with the longer focal lengths to be very useful for anything.
Then I bought a custom 30W laser from opt that was build on a different platform. You can see them on their website, but these are more in their line of custom industrial lasers, they aren’t really meant as CNC laser heads - but I wanted to check it out for fun, so I got one and built my own set of air assist nozzles for the 75mm and 150mm lenses.
This is what it looked like with the 150mm lens and nozzle:
This laser had a lot better internal optics to precondition the beam, and then the focusing lens was much bigger. This allowed it to have a tighter beam, even at 150mm focus.
However, this laser was very big and heavy, and very expensive…always tradeoffs in engineering
I don’t think this would be a practical laser head for many people.
There are other means to improve things, but they all involve a lot more money and physical size.
Every generation of diode lasers get a little better. They have to fold more diode beams together for higher power (because as of today, I think the most powerful laser diode is still 6W), and try to make the quality of that beam just a little better. So for example, the new Opt XT8 has 8 diodes, and can make a spot a little smaller than the 15W laser did, and the focal lenght I think is somewhere around 45mm. They have to keep the cost in the same ballpark on every generation or they will move outside the price/volume sweetspot for most consumers.
So in the end, there isn’t a simple fix (and if there was, Opt and everyone else would be selling those lenses). So for me, I just buy the latest and greatest when it comes out, which gives more power and a better beam with every generation. The XT-8 will cut 1/4" (6mm) material as fast or faster than the 15W would cut 1/8" (3mm).
If Opt follows their past 6 years trajectory, I would expect a new laser head model in the next year or two that is maybe 80-100W, and hopefully a longer focal length too.
To me, the ultimate laser for CNC cutting would be something with 100W, 75mm and 150mm lens options, and a 0.005" (125micron) beam width with the 150mm lens and maybe 0.002" (50micron) with the short lens. This laser would also do just about any engraving you’d want to do with those specs as well.
I’m guessing it will be 5-10 years before that is available, and it may not be <$3k either.
Thanks for that Jim.