G8 Solutions

[snakeyes]

Hello All, ok so first time with a G8 lens here and im coming to all of you with a little bit of displeasure. The tube seems so short! By the time i get the beam focused how i want, i only have one spin left in the barrel and then it falls off. Has anyone came up with a solution for this? Does anyone make some type of adapter or extender or a better tube? On top of that it is so loose. Has anyone came up with any solutions for the loose thread pitch? Lots of play... too much for my liking.

Also i broke my G8 :/ by over tightening it.

 

[Philipnzw]

The G8 lens is basically the longest focal length lens we normally use for our lasers. This means it has to sit quite far away from the emitting point of the laser diode, to get a good infinite focus.

The length of the G8 lens holder isn't a problem. Even if it was longer, it will still need to sit far away from the EP and thus the same problem occurs (lens only has 1 or 2 threads to catch before dropping out)

A loose thread between module and lens barrel is normal. Its a M9*0.5 pitch after all, so getting perfect CNC dimensions for it will be very hard/ too expensive to mass produce. Furthermore, the better modules are 99% pure copper (soft metal) so its even worse to try to cut a precise thread on it.
You can put a spring in the module to hold the lens barrel tight, it works nicely but you might feel the spring scratching around when you adjust focus.
Another method is to use some PTFE tape and wrap it around the lens barrel, IMO it gives a way better feel than using springs but you do run the (small) risk of loose PTFE tape coming apart and permanently burning onto your LD window.

One of our members here Trinh Hong Phuoc has created a custom copper module that is designed with the G8 lens in mind. The key to fixing the problem is getting a longer module, with longer threads. See https://laserpointerforums.com/threads/new-copper-aixiz-for-g8-lens.104984/ for reference. I happen to own some of these modules and i can say that they are darn near perfect. Even the threading in the barrel is very smooth. You can contact him to get hold of some of those modules.

Other than using these modules, there is little way to use the G8 lens. Though you can also go down the route of making a custom G8 lens holder with CAD software and having that custom made, but it will be a PITA and also cost a lot.

 

[snakeyes]

So the piece that Trinh Hong Phuoc makes you can only use if you modify where your current diode sits and extends the barrel length by moving the diode back. There no option for just a male to female adapter that would allow the stock barrel of the g8 to thread into.

 

[Philipnzw]

So the piece that Trinh Hong Phuoc makes you can only use if you modify where your current diode sits and extends the barrel length by moving the diode back. There no option for just a male to female adapter that would allow the stock barrel of the g8 to thread into.

Uhmmm basically his module is just a longer version of the standard module, to facilitate the longer focal length of the G8 lens. You don't need to do much, just press your diode into his module and it will work with a G8 lens. No need to move your diode position around or anything.

As I said, technically it is possible to make an adaptor/ custom G8 lens barrel to fit the standard module but it will take a bit of CAD design and trial and error. If you must absolutely go down that route then you can always contact Trinh or Lifetime17 to machine a custom adaptor for you. But in my opinion it is very difficult to design and machine such an adaptor so you are better off if you use Trinh's G8 friendly modules.

You can also go with a G7 lens. The lens has a shorter FL so it doesn't sit that far away and thus will work nicely with your current module.

 

[FireMyLaser]

I have the same issue and Aug refuse to recognize the problem. My advise: don't buy G8 until DTR looks at them.

 

[gazer101]

Whats the benefit of G8 over G2 anyways? It doesn't seem to be a whole lot cheaper...

 

[FireMyLaser]

The long focal length gives very low divergence. If the lens would stay in housing....

 

[RA_pierce]

The long focal length gives very low divergence. If the lens would stay in housing....

Yes. Another consideration with long focal length lenses is that the diameter of the lens should also increase in order to maintain maximum transmission. This is especially important for high-divergence diodes.
If the "raw" output of the diode is highly divergent, a small diameter lens like the G8 will not capture all of the light and will "clip" the beam.
This can result in internal reflections showing up in the output as well as reduced power.
The modules we use commonly are very limited in terms of lens choice and are best reserved for low-power single-mode diodes or with the use of short focal length lenses with a high numerical aperture.

I find that the G2 lenses are very effective for single-mode diodes when a 10-20% (sometimes close to 30%) increase in power (compared to longer focal-length lenses) makes more of a difference. My reasoning is that an improvement in optical efficiency allows the drive current to be set more conservatively resulting in less heat generation (thus more compact build) and longer life of the laser diode. I have some "special" single-mode diodes that I prefer live a long time rather than burn bright and die early.
With high power laser diodes, you will need a big heat-sink regardless, so the improvement in divergence and beam characteristics may be more important for the typical project.

Addendum: something I've done, which works pretty well if you can do it carefully, is to remove and then reverse the lens element in the threaded housing and insert it "backwards." This allows you to thread more of the housing into the module. If you can't keep the lens clean and avoid scratching or touching it while doing this, you're probably better off improvising a different solution or getting an extended module.

 

[gazer101]

Right

But in the long run lasers aren't particularly good long-distance burners... even the military with their big bucks weren't able to get a laser dot smaller than the size of a football 1km out (see YAL-1)

 

[FireMyLaser]

My own fix was installing a 4mm long brass tube as a spacer and then reassemble it normally. This puts the lens near the middle of the threaded housing like it should be. But because the tube is hand cut, the ends are not perfectly parallel and puts a tiny tilt on the lens relative to the housing, so there are some offset artifacts around the beam. I don't recommend this method very much unless you have more precise methods available. At any rate, one should not have to do this in the first place.

 

[RedCowboy]

It would be difficult to make one length of module that works perfectly with all the lens options and all the different laser diodes perfectly so we have to compromise........that said a longer lens barrel that's basically an inside and outside threaded tube with a screw in lens seat and screw in retainer would allow us to fine tune the lens placement to each different diode.

That is for the G8 use a lens barrel without a machined in lens seat and make the lens seat adjustable just like the retainer and then we could choose from different lengths of inside/outside threaded lens barrel tubes to suite our needs for different diodes rather than making longer and shorter module heads.

 

[FireMyLaser]

I tried G8 with 7 different single mode diodes and the lens stick way too far out on all of them, and does not work with red at all. Infinite focus happens before the lens even touch the housing. This does not seem like a compromise to me, but failure in engineering.



The reds had to use standard acrylic here.

 

[RedCowboy]

I like the G3 for single mode diodes as the G2 ( which has many uses and is a great lens ) makes a wider beam far field and a much bigger box artifact near field......the G8 is useful for many MM diodes and I use a drilled out module end to lock in my infinity focus but this is a hobby and sometimes we have to improvise, a longer module cavity may be needed for some diodes or just use a different lens.......I suppose a note that some diodes will need a longer threaded lens cavity than the " standard " would be a good inclusion in the G8 advert.

I have long wanted to see wider lenses and wider modules with wider and longer threaded cavities but we can make or have made what ever we want, however taking advantage of what's easily available and very affordable means knowing emitter geometry is different from diode to diode and divergence varies so not every lens available will work perfectly with every diode in the standard module.

Another thing I have done is to use a drilled out module end in my heat sink after the module, I have done this to use the sanwu G7 with some diodes in the past.

 

[FireMyLaser]

If we don't point out the flaws then it wont get fixed. This could easily be fixed. I told before that the G3 is also flawed, as it has a too narrow aperture and clips the output. The G3 essentially is the same as G8, focal length-wise.

 

[RedCowboy]

I know, I remember talking to you about your cool project before, you wanted the same lens for all diodes and you did not want to compromise....hell I don't like having to compromise either but I like good results better so........

I think a screw in lens seat would be the best " fix " other that a wider/longer module cavity for wider/longer lens barrels but as it is we are running short of drivers and the 20mm pure copper modules are in short supply, I expect maybe the machine shop is dealing with covid or something, who knows......but we all know DTR has been a real asset to the community and done a lot of great stuff and right now is not the time to be critical of every detail, maybe later when things are humming along we will see more options, but for now we have to compromise and hope DTR stays around doing what we love.

Something I do to remove the wide overspray and lens flair is use a length of rolled up cardstock around my lens to soak up any flair and this gives me a clean beam.

 

[FireMyLaser]

No I don't criticize DTR, rather the manufacturer. Unfortunately there is so little info and specs on these lenses that one can't know what to expect before buying, but all this could just be asked from the manufacturer, as well as requesting to move the lens further into the housing.

It should not have to be like this with word of mouth and searching old threads for clues.