Interesting. Here in the Philly area we use “Three more Doritos.”
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Oooh soooo bookmarked!!
So, is the engrave not only smoother looking, but still clear enough to see through? Assuming that is not opaque acrylic… And also, if edge lit, what is the effect I wonder?
Looks great though! 
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It’s on a transparent dark red acrylic. The engraved areas have a matte finish now that are going to work really well backlit (the backs will be sanded to help this). I should hopefully have some photos of the finished product this weekend. They’ll be going to their first convention with the new costumes
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I bet that this defocused setting would look really sharp on acrylic used in edge lit projects. I am working on some projects now with the present laser machine that I own. I may have to try the defocussing on it also. I can’t wait to get my email!!!
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How does defocused work on extruded?
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Such a great tip!! 
Thanks!
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Wow, this suggestion just cut down my cut time by 1/3 AND made it look soooo much better!
I wish I’d seen this 48 prints ago.
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I am curious then, if you changed the focus height from the proofgrade setting or camera read, what do you change it to? Less or more?
the only variable that matters here is distance from the surface, so whether you choose below or above, it should be pretty much the same.
beams are focused like this:
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okay thank you. Wow a little over my head the actuals of this, but the basic answer you gave of either way is very helpful! Thank you 
Yeah in theory. I wonder how much difference you see due to divergence due to imperfections in the lens and overall divergence in the beam? I’d imagine it’s pretty much negligible but seems to me it’d have to be nonzero?
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Yeah no way to tell really, or to know if it was happening whether it would be worse on the top or bottom of the convergence. Sometimes you have only one option as far as defocusing anyways based on material height.
In my head, however, it seems preferable to focus below the surface.
Here’s an interesting excerpt from a random paper found online (that’s actually about laser welding in the automotive industry - but could still apply here)
It has also been found that focusing in a plane above the surface results in a rapid reduction in penetration depth, but this is much less apparent with distance below the surface, within the material.
(src: https://www.phase-trans.msm.cam.ac.uk/2011/laser_Walsh_review.pdf pg. 7)
If this holds true to our applications, it seems like you could use this to achieve different effects, without worrying as much about power (introducing focal height outside of material surface is introducing just another variable to the project), so it may simplify things a bit…
Either way, found it perhaps relevant to the discussion.
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Yeah makes sense. The cone shape of the beam will extend, decreasing the angle at intersection as focal range is increased. Angle at intersection also indicates power falloff based on focal distance delta.
I bet it wouldn’t be too hard to come up with an equation that will calculate the exact same spot size based on positive and negative focal distances.
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I usually do it the other way - defocus above the acrylic to smooth the engrave. I figure I’m getting overlapping passes with a thicker beam than if I focus inside the material where somewhere in the depth it’s still going to be at its narrowest.
Haven’t done comparison tests though.
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So I tried de-focusing my engravings in acrylic (as they are always very linear and not smooth) and the engrave didn’t even break the surface of the adhesive paper on the acrylic. The acrylic was .125 and I set the focus for .25 and .20, both with same results. Does anyone have any advice to achieve the smooth results as discussed in this post?
Try .3” full power
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I defocused by 1/4" - so for yours .350 and made no changes to power. Not cutting through the masking makes me think your power accidentally got adjusted when you were messing with the focus height.
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That is an incredible difference
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