The power is being lost where it’s not being applied to anything useful anyway (i.e. it would’ve been curing flakes, now it cures nothing).
The reason it cures flakes is because it keeps retracing the same area over and over again, so cumulative exposure over hundreds of layers amounts to - a half cured flake.
In other words, very little of the total radiated power is blocked, and the amount that was blocked is not doing anything useful anyways.
I compleatly agree with you that given Option A: Cure unwanted stuff and Option B: Cure nothing. Option B wIns. However @Randy_Cohen is right that it is pulling power that if the laser where configured correctly would be curing what you want. This could result in less focused curing on the outer layer and therefore less detail, or undercuring of the infill. But you know all of this.
Did you get your printer yet?
So here’s a video of installing a second choke: https://www.youtube.com/watch?v=z7AiD0EpBzY I use a mouse click macro recorder to loop the laser spot test for the install.
This is the first test result with that new choke - little bit flakier than the first one, but still a world of difference from the unaltered machine.
Great job @KevinHolmes, thankyou!
Do you have any theories as to why your right hand cross in all your pictures isn’t as as good as the left?
The reason I ask is because I get something similar and I it the same side that is always worse.
Kevin,
If I’m understanding this correctly, the bent plastic adjusting part is is distorting the shape of the silicone sleeve on the flare side and preventing that light from being emitted. Is that correct? OR is the bent part of the plastic actually preventing the light emission?
Is there a reason that a simple wafer with a hole of the ideal diameter in it, affixed to the outside would not work too?
-C
@Steve_Johnstone still a mystery to me - maybe something to do with the different angles the flare has on different sides of the build platform - causing it to interact differently with the in-fill pattern? but I’ve yet to think of something convincing
@ChristopherBarr no, the plastic bar is the choke - as per the second beam diagram in the op. If you skip to the end of the youtube video a couple of posts above you can see the effect as I apply/adjust the choke by pushing it in to the laser barrel. The silicone ring is just there to hold the choke in place - and allow it to be adjusted.
As for a simple aperture outside the laser barrel - this has been much discussed - see the op and the links there.
This looks very interesting:
http://iopscience.iop.org/2040-8986/16/7/075301/article
Any chance you can show us a laser spot test after your modification?
So, this would be a potential option?
http://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=207&pn=D5S
There’s even cheaper stuff on ebay. you’d need a way to mount it of course, and that should be axially adjustable, but could probably print something up.
@Kevin_Grisko see the end of the you-tube video in post 24 above - a spot test on it’s own doesn’t show you the contrast, and I have another test print running at the moment.
@ChristopherBarr you should read some of the background - when I said a simple aperture external to the laser has been much discussed already, I meant that it has been mostly discounted - mainly because of this Form1+ laser flare issues illustrated - pics and video and this Form1+ laser flare issues illustrated - pics and video
I say mostly - because of course @JoshK had his success - but then sold his printer, so there was no follow-up and I really don’t think it’s a practical approach because of the reasons listed above.
The beam profile as it exits the laser is actually quite large - almost 1mm square (it’s literally square) - with no flare that can be trimmed away with an aperture,
It’s not until the you look at the beam profile about 15cm from the laser that the flare begins to take form.
then what is that black piece of plastic you’re using actually do? it’s right up against the laser, no?
@ChristopherBarr the point is that the flare part of the laser beam profile is already merged with the main beam pretty much at the laser barrel face, but the flare light actually comes from close to the lens edge - the trick is catch it before it becomes part of the main beam.
By putting the choke inside the barrel and pushing it up close to the lens the flare part of the profile can be picked off almost entirely separately from the “good” light.
Interesting video. That’s some McGyver s**t right there. Great job Kevin!
But what’s more interesting…watching that video on Youtube, and because of your video title description, at the end of the video I was presented with lots Karate Choke video instructions, which were equally informative! lol
Now I know how to fix a laser flare and to choke someone at the same time.
Also if you choke someone while holding a laser you could leave them blind too! Laser-Fu the ultimate martial art.
From everything i’ve read, i think the “missing” power is well and truly compensated for.
I.e. except in very extreme cases, even though there’s some fraction of the output power being irradiated into the flare, the resin cures just fine at the hotspot with what’s left. In fact, i wouldn’t be surprised if Formlabs measures the hotspot intensity with a photodiode and tweaks the output power on a per-printer basis before shipping (at least i would - the output power can vary greatly with the current and individual laser diode samples).
In other words, you can just ignore that part of the total output and pretend it was never there in the first place.
(Although i’m sure there are extreme edge cases, but in those, people usually complain about getting nothing but jello and simply return the printer to Formlabs straight away.)
Yup, i picked it up from the DPD depo on Tuesday i think.
Unfortunately, my week at work’s been so crazy these past days i didn’t even unpack it yet.
It’s still sitting in the entrance hallway, in the unopened box. 
@Kevin_Grisko here’s two fresh shots of my spot with and without the choke … I had to remove the choke again and re-install it, but that’s ok, I had it set too aggressively anyway - it’s better now …more on that tomorrow.
Without
With
Finally unpacked my Form1+ (ThoughtfulFox).
Was too tired to do anything but a quick laser spot test.
I’ve got the same beam profile as everyone else, but to my eye, the central gaussoid is orders of magnitude brighter than the flare. The flare opposite to bunny ears is about the same brightness (or at least the same order of magnitude) as the bunny ears, just shorter and thicker.
I don’t wanna jinx it, but to my eye, although it’s not what i’d call a nice, clean beam, it’s still decentish.
Hopefully will catch some free time to do a test print soon.
YAY \0/
You finally got your printer!
Only printed a butterfly clip, printing a rook now.
So far so good.
Although i’ve got clear resin in the tank, so i can’t really judge the surface quality yet. Gonna play around some more after the rook, print some stuff i wanted to print in clear anyway, then switch to black and do some surface quality tests, hopefully.
A few things i’ve noticed (sorry for going off topic):
1) The PDMS layer in the tank (well, the one that came in the printer, haven’t unpacked the extra one) seems to be seriously badly leveled. Like, 1mm of a difference between the hinge and peel sides.
2) Quite a bit of “dust” in the vat holding rails, i assume from the anodization process - wiped that off immediately after unpacking, haven’t inspected the main mirror yet. I’m going to continue using it straight out of the box, until i run across the first issue, instead of stressing about things straight away.
3) Jesus christ the Formlabs resin is thick and sticky. Unlike Makerjuice, it can’t be washed off with hot water. Good thing it “de-stickifies” after a while in open air.
4) The lead screw seems to have a very very slight wobble, but it’s not an issue, because it’s fixed in only two points (the platform and the stepper). Happy to see Formlabs didn’t make the usual mistake of over-constraining it by fixing the top end - that would actually make any wobble an issue (because it would move the “peak” towards the middle).
5) Interesting to note that there’s a varying strategy for both curing and peeling as the print progresses beyond the first layers. I was wondering if they did that, as i do something similar on my DIY thing, although in a very manual fashion (by changing the gcode for first vs. further layers).
6) Rinsing the platform with the print attached in hot tap water helps with removal of the clear somewhat, as i’ve guessed (i use that on Makerjuice, was wondering if it’d help here).
All in all, still very very early for me, but this has got to be the most painless first print experience i’ve ever had.