GaAs lens part II -

Tried my new ebay GaAs lens last night- First on some stainless, used it to run the outlines on one my big operator panels (header plate)-
I was pleasantly surprised to find the Cermark was noticeably darker than I've been getting--

Thinking all was well, I used it to etch one of the largest black anodized operator panels I build from scratch.

Whoops. All is not well with these lenses-- I actually hope my customer buys this thing. From arms length, I would guess most people would think the engraving is fine. But we who do this for a living certainly won't!

Once the panel was engraved, I found the engraving was, for the most part, barely evident- not enough power. So I added 5%, and eventually found I needed a 7% increase to equal my usual results.

When I finally finished, as usual I took a good look at the engravings overall look and quality. And I'm always amazed at the top-notch engraving I get from the Triumph...

--last night I removed the lens housing to see why it or the the lens was loose. I seriously thought one of them HAD to be loose.

Nope. All tight. And I was now equally amazed that just using a different lens could make such an astounding (< insert favorite radical adjective here) difference in the engraving quality!

So I ran this test this morning just to verify I'm not imagining things...


first pic, top line I ran using a new 'regular' $18 ebay 2" lens, 500mm/s .05 gap, 25% power.
I moved the plate, changed to the GaAs lens, and ran the same job. Not enough power..
Next one down was at 30% power, bottom line at 35%, finally close to the same whiteness..
Attachment 360537
Aside from the extra power needed, the difference in engraving quality is glaringly obvious..
this text measures 3.3mm in height btw...

I turned the piece around and ran a 'controlled' test.
top line is the GaAs lens at 35% power,
bottom line is the normal lens at 23% power (my usual setting for black anodized)
-I actually ran the second line twice since this alum is from a new batch which gets a snick whiter with 25% power,
but the second run blew away about half the alum oxide. The top line removed some itself, just not nearly as much.
But my main concern is the side-by-side engraving quality results...
Attachment 360538
Attachment 360539
Attachment 360540
-even without enlarging these thumbnails the results are obvious... normal lens engraves with crisp lines and corners, radius's are mostly round & smooth... GaAs lens, NOT... And I engraved an entire panel with the 'bad' lettering...

In 15 years of Laser engraving with 4 different machines and the possible variations between them, I've NEVER seen much if any engraving differences between them. I've even tested my cracked and spot-stained lenses against my good-condition lenses and have never noticed a discernible difference even under magnification. But this one lens created a night-n-day difference, which I honestly didn't expect.

One good thing may come from this lens however, it may actually help with my Triumph's Cermark engraving. At least on larger than 3.3mm text ;) -- more experimenting coming...

Dave Sheldrake is always telling us lenses and beam quality matters-- Yes, it does! :D


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The new lens doesn't appear to be as sharply focused. Have you verified the focal length of the new lens, and adjusted accordingly for each lens in this test, or did you just run both at the same focus setting? I've found that different (supposedly) 2" lenses have different enough focal lengths that I need to adjust the focus tool for the specific lens.

Good call on the focus Glen-- all of my other 2" lenses are very close to one another in focus range, but this new one is pretty different, more than I expected.

After running my version of a 'ramp' test and finding the sweet spot, the engraving quality improved big time!

I still wanted to do a side-by-side comparison. Only this time I used the worst other 2" lens I have that's still in one piece...

Elements of the test: piece of black anodized, various numbered focus 'tools', which look like a ramp when stacked together ;) --
and the 2 lenses I used.
Attachment 360612

not kidding about this lens still being in one piece--
Attachment 360613

-I'm surprised it is, and 2 halos for good measure. If any lens should engrave badly, this is it!
Attachment 360614

I stated with the new lens, correct engraving on the right, and worked my way down from the longest to the shortest focus tool,
each line states the focus difference from my 'zero' red tool. Then I flipped the text and engraved the reverse text with the old lens.
The old lens actually looks better at +.025, while the new lens favors somewhere between -.08 and -.105, which is getting close
to a full 1/8" difference in the sweet spots, and the new lens still engraves fairly well at over .155"!
Attachment 360615

But the new lens quality is MUCH better now! In this pic I re-reversed the old lens engraving, it's the bottom 3 lines, the new lens
is the top 3 lines. Much closer in quality now! Yet I still think the old lens is just a snick sharper, but it takes magnification to see it.
--Surprising that a broken stained Chinese lens can equal or best a new GaAs lens :)
Attachment 360616

So the reason for the bad engraving was the increase in power it took to get a decent burn. With my laser's tendency to engrave long expanses- long parts of E's, T's, etc, which you can see in the pics- at higher power than the short expanses, the extra power just exaggerated that effect.

I really didn't expect the focus point to be so different with the new lens. Just goes to show it IS a good idea to test every lens :)

If I clean my lens or change it for any reason I vector cut a couple straight lines first. I can see right off if the lens is way out of focus by the thickness of the line being cut. then I can fine tune the focus from there.

Can easily be +/- 1.5mm on lens's Kev, especially when moving from ZnSe Meniscus to GaAs Plano - Convex :) Yup, quality matters, both beam and lens, if anything ..more lens.
I tend to go with GaAs on a lot of machines as they don't scratch so easily when a ham fisted operator tries cleaning it with their T-shirt but use high grade ZnSe from Mueller etc when it's something critical as I can't tell if there are any problems *inside* a Gallium by looking at them