45 – Photo Laser Engraving Acrylic with a Compound Lens (48:13)

The Lightblade Learning Lab with Russ Sadler

The Lightblade Learning Lab is a series of videos that Russ did for Thinklaser Limited based on using the Lightblade 4060 Laser Cutting and Engraving Machine. Thinklaser’s Lightblade 4060 has a 400 x 600mm bed size and was supplied with a 60W EFR laser tube. In this session, Russ does some experimentation relating to Photo Laser Engraving Acrylic and is able to engrave at 635DPI.

Photo laser engraving acrylic - tiger image at 635 dpi
Photo Laser Engraving Acrylic – Tiger Image at 635 DPI


  • (Obtaining true 635 dots per inch, photo quality laser engraving.)
  • Importance of dot size (see the OPHIR website here about different types of lens.)
  • Different lenses – ‘Plano-Convex’ and ‘Meniscus’ types and production of focus point.
  • Spherical Aberration.
  • Parallax Technology Inc website – interesting lens information in the FAQ Section.
  • Energy profile at the dot.
  • Difference of effect of over-burning between organic materials and ‘binary’ materials.
  • Custom-made Delrin secondary lens-holder fitting for standard lens tube containing 4” lens to make a compound lens.
  • Testing the new lens assembly on Acrylic with Russ’s standard test pattern at different focal distances using the laser in ‘Common Mode’.
  • With the best focal length, testing with different power and speed settings.
  • Using ‘Special Mode’ to try to get less power into the dots.
  • Testing the scan line offset compensation.
  • Introducing a new piece of software called LIGHTBURN.
  • Importing a graphic and setting the ‘Cut Settings’ including the ‘Newsprint’ function.
  • The Preview feature.
  • Testing the engraving on the laser at different resolutions up to 635 DPI.
  • Looking at the results of the ‘Newsprint’ and ‘Jarvis’ dithering functions under a microscope.
  • Re-testing with different settings.
  • Looking at the difference in the results between extruded and cast Acrylic.
  • Summary

My thanks go out to Tom at Thinklaser for giving permission to embed these videos on this site. If you are looking for a new laser machine from a quality supplier, then I would suggest you check out their website: www.thinklaser.com.

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Transcript for Photo Laser Engraving Acrylic

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0:10Well, welcome to another Lightblade Learning Lab. Now I’m literally just

0:21cleaning my table here, I’ve already taken the muck off with some acetone but

0:27I haven’t been able to get rid of some of the marks. So I’m afraid I’m being a little bit er…. we’re using some abrasive.

0:38That’s just a little bit of a spring clean before we start today’s session. I’m not boasting about the inside of my machine what I’m really going to do is

0:47give you a little observation test now, you’ve got ten seconds to tell me what’s

0:53different about this machine? Nine, ten. There you go you’ve had your time, I’ve got a

1:01completely different arrangement just here. Now in today’s session we will eventually get round to engraving on this material, clear acrylic. Now you’d

1:12think that it was a very easy material to engrave on because it’s a very soft material and it burns very easily and you’ve heard me extolling the virtues of

1:19this material many many times. Sadly it’s not an easy material to

1:27engrave on, you can get it badly wrong and so consequently what we’re going to

1:32do is we’re going to start off by explaining the process by which I have

1:37gone through and successfully started to engrave on this material. Although today’s

1:43session is going to finish up with engraving acrylic, we’re going to have to

1:49start off from a completely different point of view. From all the work that I’ve been doing recently I have become very very aware of how important it is

1:58to get the dot size correct. Now the dot size is completely controlled by the

Transcript for Photo Laser Engraving Acrylic (Cont…)

2:07lens, so I’d like you maybe to go and pick up this document from ophiropt.com

2:14and take a quick read of a little dissertation that they’ve got here about

2:20different types of lenses. Now this one is what we normally put in our machine and it’s a Plano convex lens. Now there’s another type of lens

2:29that we can get which is this one which is called a meniscus type lens, which has got a concave bottom to it. So here’s a larger picture of what you’ve just seen

2:41there and there are two major factors that basically affect the thing that

2:47we’re really interested in which is this focus point here which ultimately

2:52determines something which is called the spot size this thing here. Now with the

2:58Plano convex lens the bigger the diameter of the laser beam itself as you

3:03can see what tends to happen is the beams come in from the outside and they don’t converge at the same point as those that are coming down the centre of

3:12the lens so we get this very strange fuzziness at the focus point and there

3:19is a limit to how small we can actually make the focus point with this type of lens. Now with this type of lens here which is called a meniscus lens we have

3:28got a much better beam path towards this area here now it still isn’t perfect if

3:35you look at this drawing carefully you’ll see that there is still a difference between the beams that come down the centre and the beams that are coming

3:42from the outside, but the difference is a lot less so this is a much better focusing lens. But the point that I’m really trying to show you with these

3:51lenses and these beams is that if we have a smaller diameter beam and we’re

3:58using a smaller part of the lens then we’re getting less spherical aberration

Transcript for Photo Laser Engraving Acrylic (Cont…)

4:03and we get less divergence at this focus point here. Now here’s some more homework

4:09for you to do. This is a company called Parallax Technology Inc and if you go

4:15and look at their frequently asked questions section at their website you’ll get directed to this 9 pages of discussion about lenses, the

4:26technicalities associated with lenses which and lasers themselves. Now it looks fairly heavy reading but in fact it’s written

4:35in a fairly lightweight understandable way. So if you can work your way through

4:40it gently you’ll come across all sorts of interesting things about your lens and the lens is the most important part of this machine, because it is the one

4:49thing that converts a low energy density beam into a high energy density beam

4:56where we can actually do serious damage to our materials and that’s what this is

5:01all about. We then move on and we start to talk about the lenses themselves and

5:09basically we’re now coming back to what we’ve just talked about here and that is

5:16that basically to minimize the spot size theoretically what we need is the

5:23largest beam diameter, the opposite of what I’ve just been talking about and the shortest focal length, and then it goes on to talk about some other

5:34features of wavelengths and various other things and then we’re talking

5:40about here, we get exactly the opposite requirement. This kind of aberration increases rapidly as the diameter of the beam increases, in other words that

5:49spherical aberration that we talked about here. We clearly saw that as the

5:55beam diameter increases the spherical aberration which is a thing that causes

6:00this fuzziness at the focal point. It basically says this kind of aberration

Transcript for Photo Laser Engraving Acrylic (Cont…)

6:10increases rapidly as the diameter of the beam increases, so in effect what we need is we want the smallest beam diameter and the longest focal length. So we’ve

6:21got two contradictory requirements here in practice and as it says here as you

6:26see these two will always fight against each other and a compromise will have to be made. Well, that’s basically the summary of where I want to finish. You

6:37can read the rest of this document on your own it’s a very interesting document. Okay so this area here the spot size

6:45we’ve talked about quite a few times before, but although the spot size is at

6:50this neck here, the beam coming into the lens has got an uneven energy distribution and the energy distribution is high towards the centre anyway and

7:00when we compress it down into a much much smaller diameter beam, that same pattern of energy density is still there. So although we’ve got a spot size here

7:10and we’ve got an energy distribution within that spot size, that means that

7:16we’ve got a very high energy point within this little spot size. So, we’ve

7:23spoken about this before and had a demonstration of the fact that we can put a spot size, we can put a little hole in our material, but round the outside of

7:33that hole there is a little halo of scorching and that halo of scorching is

7:40in fact the spot that we are going to see when we do our printing. Our

7:48conversion of a photograph into a laser dot, so a pixel may be point one, but this

7:59but the dot that we’re going to put on that pixel could be the best that we can normally find is about point two. Now I’ve been struggling with one and a half

Transcript for Photo Laser Engraving Acrylic (Cont…)

8:09inch lens, two inch lenses. I’ve been struggling with all sorts of things trying to find that maybe a power at which we can set this this point, we have

8:18a little point in the middle but we’ve always got our burn mark around the outside. So that means if we’ve got a practical dot size, the smallest that we

8:27can sensibly get which is around about naught point two millimetres diameter, that determines the resolution of the picture that we can print with it and

8:37that resolution turns out to be a hundred and twenty seven pixels per inch, which is quite a low resolution picture. So if we want to increase the resolution

8:49of that picture we’ve got to find mechanisms for doing it. One of the mechanisms would be to try and make the dot smaller so that the scorch mark

8:59is smaller. If you look around at somewhere like Thunder Laser they claim

9:06to have something called a high resolution lens system and that is basically some

9:12sort of compound lens system which allows you to get a smaller spot size. I believe they claim resolutions up to a thousand pixels per inch.

9:22Now I really can’t believe that, because of the physics of producing a brown

9:28scorch mark on organic materials. Now I’m using those words carefully, “organic

9:35materials” because not all materials produce a scorch mark and that’s where we are working our way around today – to acrylic. Now acrylic does not scorch, it

9:47only evaporates or melts. Now we’ve seen with another binary

9:55material; anodised aluminium that we can do some quite interesting things with

10:01resolution, even using just a one and a half inch lens and limiting ourselves to this probably 0.15 ~0.2 diameter dot. We can get better resolution. Now the

Transcript for Photo Laser Engraving Acrylic (Cont…)

10:14problem with organic materials is that if you burn the same spot more than once

10:20or partially / part of the same spot more than once for example if we do something

10:25like this and we finish up burning this same area in different directions. We

10:32shall find we shall finish up with a multiple burn in these areas. The dots

10:37will get deeper and deeper and deeper and that’s how we get the 3D’ness into a wood or a paper surface. It’s not real 3D’ness, it’s just over burning.

10:47Whereas with an aluminium oxide and an anodised aluminium surface you evaporate

10:54the dye but you do not remove the oxide layer itself so no matter how many times

11:00you over burn the same area you’re only going to remove the dye,

11:05but if the dye has already been removed you can’t remove the dye. So consequently over burning on some materials is not effective, it doesn’t have any effect at

11:17all. As I said, anodized aluminium is a specifically beautiful material to allow

11:23us to do more than we theoretically should be able to do, but that’s not the

11:28same situation with acrylic. Although I do believe that acrylic is better than

11:34an organic material because it does not scorch, but what we’ve got to do is to

11:41try and find a way of making the dots as small as possible, so that we only

11:48produce minute little dots on the surface of our acrylic. Acrylic is a

11:54funny material, because when you put a very small dot on the surface it doesn’t

12:02actually turn white. It looks as though it turns white, but it doesn’t. All it’s

Transcript for Photo Laser Engraving Acrylic (Cont…)

12:07doing is catching the light in a different direction but the first thing we’re going to look at is the different nozzle arrangement that I’ve got on my

12:16machine here. Let’s look a little bit closer at this. Now I just happen to be using a piece of flexible silicon pipe, but I could equally well have used a

12:25piece of polyurethane four millimetre diameter pipe, that would have done exactly the same job of poking up inside there, like that and slipping into that

12:36hole there. I mean the principle is all I’m trying to do is get the air assist into here without using this big bulky fitting. We remove the lens

12:45and what we have here is a piece of Delrin which I have machined and I’ve made

12:53it a push fit and it is a nice snug push fit onto the outside of this normal lens

13:03tube. Now there’s no lens in the bottom there but there is a lens in that end.

13:11That’s a 4-inch lens that has been supplied with the machine, in other words

13:17what we’ve been able to do is to reduce maybe a ten millimetre beam as it comes in here down to three millimetres or four millimetres by the time it gets

13:26down to the bottom here. Now normally it would be coming down a further inch or

13:36more and the focus point would be about six millimetres below the bottom here

13:42well that focus point is no longer down there because what I’m doing I’m intercepting the beam just here. As I said at that point, it’s probably

13:52something in the region of about maybe three millimetres diameter and this is

13:58where I’m doing something different. Now this rather special lens holder that

Transcript for Photo Laser Engraving Acrylic (Cont…)

14:06I’ve arranged here, and yes it is a lens holder because what I’ve got in here is

14:12nothing more than a little seat. See the lens is sitting in a little seat in

14:18there, then it’s sitting just above the surface there

14:23and so consequently what I’ve also got is a little a plastic ring that I’ve laser-cut that sits in there on top of the lens and as I push this into here

14:39like that, I’m actually clamping this onto the plastic ring which in turn is

14:45clamping the lens into its seat and it doesn’t shake. It’s covered completely and safely clamped everything up, so now what I’ve got is a compound lens

14:56assembly where this one and a half inch focal length lens instead of a 10 or 12

15:02millimeter beam hitting it it’s got a three millimetre beam hitting it. In

15:07other words, we’re using just the central part of this second lens to focus the

15:13beam even further. The net effect of that is that this one and a half inch lens

15:18seems to come down to something like almost a three quarter inch focal length

15:24lens and it produces a very small spot and so what we’ll do we’ll just

15:31experiment with that and I will show you what I mean. OK now we’re going to do a series of tests on here which are most important that you do these tests before

15:40you even start to think about doing engraving. We’ve got our piece of clear

15:46acrylic and I’ve got the focus set up to four millimetres. I’ve got the power set

15:53very low at about 12 percent and I’ve got the speed set to be a hundred, I’ve

16:00actually got it set to 150 because I know that this machine has actually got a very good fast responding power supply. So I’m fairly confident that a hundred

Transcript for Photo Laser Engraving Acrylic (Cont…)

16:10and fifty millimetres a second is not going to be too fast for this test.

16:18But what we’ll do we will go and look at that under the microscope to see the results of these tests. Now I’ve got one of these which I can examine it and I

16:28can tell you that is rubbish. So we’ll now increase the focal distance

16:33to five millimetres and we’ll do the same thing again.

16:44Hmmm still not very good, now we’ll go up to five millimetres, it’s starting to get

17:01interestingly good’ Let’s try six millimetres and that’s beginning to look

17:09quite nice we’ll try seven millimetres, now I think it’s

17:19just gone past its best so I’m absolutely convinced that six

17:25millimeters is the right focus point. So we’ve set a nominal power, we’ve set a

17:33nominal speed just to get the focus that doesn’t mean to say we’ve set things

17:40what we’ve now got to do is to play with the power and the speed to see if we can

17:45get a nice crisp dot. Let’s go back and set the ideal focus which is six

17:51millimeters, now we started off with 12% power the dots are more or less touching

17:58they’re still point two dots we’re trying to get the dots smaller so

Transcript for Photo Laser Engraving Acrylic (Cont…)

18:03technically the only way that I’m going to be able to get those dots smaller is to reduce the power or increase the speed to put less power into each dot. So

18:14first of all let’s decrease the power, but I’m already down at 12% I can’t get down much below ten. I might be able to get to nine percent with this

18:24particular machine, but let’s just try 10% and see what we get and we’re still

18:30running at 150 millimetres a second.

18:37They’re not bad dots there’s a space between them, I would say that those are

18:43roughly point one five diameter the dots that I can see there which is an

18:52improvement on what we’ve been able to get before. Can I get any less power

18:58let’s try 9%.

19:03Well 9% power produces some really really nice dots but not many of them

19:11they’re very inconsistent. We actually have got 0.1 dots absolutely amazing

19:21never seen that before. 10% was nearly there, 9% gave me perfect

19:27dots but not enough of them how can we find small dots? There is another way to

19:35get less power into those dots and that’s with something called special

19:40mode, at the moment we’re running this machine in standard common mode. If I go

19:46to my user settings and write back into the machine that I want to move into special mode, let’s do that. Now because I’ve moved into special mode the power

19:57will have dropped off considerably and so what I’ve got to do now is try and find a new power range that’s going

Transcript for Photo Laser Engraving Acrylic (Cont…)

20:06to work for me. I know it sounds very strange but I’m going to move from nine percent all the way up to twenty five percent. Now I can guess this number

20:14because I have used special mode before, 25 percent power and a hundred and fifty

20:20millimeters a second and I can tell you that they look pretty good but the dots

20:27are just about touching so 25 percent power all the dots are there, but they’re

20:35still just a little bit big. So this is 20 percent power and my goodness may

20:46they’re beginning to separate out now I can soon see gaps between the dots.

20:59Well I think that 18 is actually even better, let’s find out what happens at 16.

21:12Well the dots are actually very nice they’re at about point 1 but we are just

21:20about losing some of them so 18 percent, we’re now going to go up to a speed of

21:26200 millimetres a second instead of 150.

21:34Well we’re beginning to lose just a few dots so it looks as though this compound

21:40lens system has given us at least 60 and maybe a hundred percent improvement in

21:50our dot size, you know it is possible that a longer focal length might

21:55actually produce a smaller spot size based on some of the reading that you

22:00will be doing. We’ve established what our settings are for achieving the best dot

Transcript for Photo Laser Engraving Acrylic (Cont…)

22:06in acrylic. Now these dots, I mean you can hardly see them and you think to

22:16yourself well okay how’s that going to work. Well it is a rather interesting

22:21problem, because we’ve only got single dots you can’t really see much when you get a group of dots

22:28the light refracts across the dots and you can see them. When you look at them straight on sometimes you can’t see the dots. This is very much a trick of the

22:38light when you’re working with acrylic. So that’s introduction number one, our

22:44different sort of lens assembly. The next thing I’m going to introduce you to,

22:50which is brand new for this particular machine is a piece of software that is

22:57in the process of being developed. It’s fairly well advanced, but it’s not finished at this moment in time, it does not completely replace RDWorks today.

23:08In a few months time, I suspect it will do everything that RDWorks does, plus

23:14some and better. The one thing that is very well established and tested at this

23:20moment in time within that software is the photo engraving side of it and so

23:25what I’m going to do is to introduce you to a piece of software called Light Burn. Now you can go to Lightburnsoftware.com and download a free

23:35version of this at the moment. It’s a 30-day free trial. I’ll stress again this

23:43is not a piece of finished software, but it’s being written by one single guy

23:50who’s devoting his time and effort to doing this for the sake of the laser community, because he like many other people are not entirely satisfied with

24:00the results that RDWorks gives and so just bear that in mind when you see

Transcript for Photo Laser Engraving Acrylic (Cont…)

24:06that he’s trying to raise a few pounds to carry on doing this development work he’s got a day job, he spends a lot of his time at night working on this and

24:15there are regular updates of the software to include new features. Now I’m speaking to the guy about it and I’m doing some test work for him, because I

24:24am very excited about where this piece of software could finish up. But I’m

24:31going to introduce you to just one small part of it today. You will see that it doesn’t look too dissimilar to RDWorks in many areas, but the way that he

24:40has the graphical interface and the user interface is completely different than

24:45RDWorks. He makes things so much simpler and easier to understand. Now

24:50there is one more important test that we must carry out before we start thinking about the actual engraving and that’s the scan line offset.

25:06Now we’ll take a look at that under the under the microscope, but I can assure

25:12you that that’s not bad we haven’t got to do any offset compensation. At 200

25:18millimeters a second and above you would have probably had to put a small amount of offset compensation in, but you’ll see what I mean the scan lines between going

25:26left and going right are pretty well lined up so I won’t get too much, if you

25:31like, dot offset because of scanning from left or from right. Now, I have to

25:38apologize in some ways because everything appears to be so small, all the icons appear to be quite small but that’s because I’m working on a 4k

25:46screen as you’re looking at here, but it doesn’t make any difference today

25:51because we’re not going to go through in detail very much about this Light Burn

25:56software, other than I’m going to extol the virtues of its ability to handle

26:02graphics and I’m going to import this tiger and of course it imports it as a grayscale image because all the color has been disposed of. Just like RDWorks,

Transcript for Photo Laser Engraving Acrylic (Cont…)

26:11as soon as you bring it in, it prevents you doing anything other than

26:17making a scanned image. It doesn’t say bitmap but it limits you to just the scanned image you can’t do a cut or anything on this. So here are the

26:27parameters for this picture and to be honest unlike RDWorks you don’t need

26:34to go anywhere else. You import your picture and then you say ah, OK I’d like

26:40to cut this at and if I remember the parameters that we are using are a hundred and fifty millimetres a second and we’re going to use 25, no we’re

26:50going to use 20 percent power, 20 percent power, 20 percent power. Okay we are

26:59going to have air assist on, bi-directional scanning yes; negative

27:06image yes; because one of the things about acrylic is that you need to view it

27:13against a black background. What you’re going for it what you’re going to produce is white on a clear background and so

27:23consequently it’s the opposite way around to normally burning black on to a

27:28white background. So we need to make it a negative image, we are going to set this

27:37at point 1 is in fact 254, 254 dots per inch in RDWorks we need to

27:49understand what the dots per inch is and set the line interval accordingly. Well

27:54I’ve just said to you the the dot is 0.1 and here we go look the line interval

27:59has automatically set itself to 0.1. Now we can play with the scan angle but

Transcript for Photo Laser Engraving Acrylic (Cont…)

28:06we’re not going to we just leave it at 0. Now we’ve got all these modes here, now

28:12these are different that’s just black and white so anything in that picture

28:18above mid grey will be white and anything below mid grey will be black so

28:24we’ll be able to convert that image into a black and white image if we wanted to,

28:29and that’s what threshold is. Ordered is and you can see what the dotting pattern

28:37is likely to be, Atkinson it’s another dot pattern; dither

28:49that’s probably much the same as RDWorks Jarvis is yet another dot pattern and that’s one that I’ve found to be very

28:59useful. That works very well, there’s a clue down at the bottom here what these dithers may be good for. Then we’ve got newsprint which to be honest

29:11at low resolution looks pretty hideous but we’re going to be using that today

29:16because we’re going to be driving this into the stratosphere where all of a

29:22sudden hideous becomes wonderful. Number of passes; well you can run a number of

29:30passes but why would you want to you know if you’re over burning you’re running multiple passes anyway but I think basically the number of passes is

29:38used for the next one which is grey-scale. Now we’re not going to be using

29:44grey-scale because that’s what you use for 3d engraving and consequently that is where you might need to specify the number of passes, so everything you need

29:53for scanning is in this one little parameter box. You don’t need to go anywhere else you just import it and you set your parameters. Okay

30:03you can’t appear to see unlike RDWorks what the end result is. You can

Transcript for Photo Laser Engraving Acrylic (Cont…)

30:10zoom in as much as you like but all you’ll see is the original picture. If you want to see roughly what the result is that you’re going to get and what I’ll

30:18do for the moment I’ll show you this we’ll set newsprint to 50, so you’ve got

30:25to come up here to the little television which is the same as RDWorks and there’s what it looks like. Pretty grim, but you can also see that it is

30:38based on drawing lines, look can you see that okay. Let’s go back and change the

30:51parameter to where we had it, two hundred fifty four, two five four okay. Now let’s

31:02go and have a look at preview

31:13and there we can see what it’s trying to do. Look it’s still trying to draw lines

31:19not dots and if you want to see how it works you set this back and you can see

31:32that it’s going to start engraving from the bottom towards the top like that.

31:39Everything is so user friendly in this bit of software it’s just well I

31:45wouldn’t say it’s unbelievable it’s just very very pleasing and satisfying to use. So there we are import, set the parameters, push the button and go.

32:06First of all I had my air assist on and normally with air assist it would blow

Transcript for Photo Laser Engraving Acrylic (Cont…)

32:12all the debris onto the all the vapor onto the acrylic and it would stick to it but because the cut is so very very light basically you can just brush the

32:25dust off. Now what do you think of that? That’s pretty amazing isn’t it. now this

32:36is double the resolution that I would normally use, this is 254 pixels per inch

32:43which is basically using 0.1 dot and that is a pretty good picture. Now if I can

32:53zoom in tight enough you will just see the dots on his nose. Unsatisfied with

33:03that, I thought how far can i push it let’s go up by another 50% and this is

33:13381 pixels per inch.

33:22now this only works because of the black background, if I lift it away from the

33:29black background you have to catch the light just right to see the image. Okay so I

33:36can push it to resolution times two

33:44let’s go up to 508 pixels per inch. Now with the naked eye I can just about

33:51see the dots on his nose but that’s a pretty good picture. So one more jump to

34:02635 dots per inch and that is to be honest getting pretty close to photo

Transcript for Photo Laser Engraving Acrylic (Cont…)

34:12quality and the other real tests as to whether or not we’re getting double

34:18cutting off or some really nasty results from over burning our pixels, is if we

34:25can feel any sort of 3Dness on this side absolutely nothing on that one

34:31at 508 pixels despite the fact that this one which is the 635 dots per inch has a

34:39slight what I think probably is over burning

34:45I actually like the contrast and the shading on that one slightly better than

34:51this one. This one when I look at it against that one has got a slightly cloudy look

34:57to it whereas this one is crisp so that is absolutely staggering that I can get

35:04up to 635 dots per inch on acrylic, but it is using special mode, that’s 150

35:13millimeters a second and I’m using 20% special mode power but I’m using

35:21newsprint as the dithering system. Now we need to go and take a look at what

35:29newsprint is and why it works so well, if I was to try and do this with any of the

35:36other dithering systems I would get lower standard of results in fact we

35:41could try that with one of the other ones there’s a good system around called Jarvis which I have tried and it works well on organic materials, but it is a

35:53dot process whereas in fact newsprint is not so much a dot process as a line

36:02process and we’ll go and understand what that means when we look into the way in

36:07which the dots are formed. Okay now we’ll look at the same thing on every picture

36:13so that you can see how so you can see how the image is changing. Now the whole

36:21point about newsprint is as you can see it’s based on a diagonal lattice and the

36:27size of the white as opposed to the black is the thing that gives you

36:33the grey-scale effect. Let’s just go in close and have a look. Ok in this

36:40picture you can see clearly what I’m talking about you got different sized triangles and different sized squares but they’re all made up of lines

36:48basically there are one or two individual pixels on there but they’re

36:53very few and far between and I think even if those individual pixels were missing it wouldn’t detract from the overall look of the picture so this is

37:03at 254 pixels per inch which is as I said normally the maximum resolution I’d

37:10be able to get with a point 1 diameter dot. Well there we go that’s 381 pixels

37:18per inch and there’s the eye again as you can see we’ve still got lines

37:24being drawn and then when we get to 635 we still managed to even though the

37:38pixels are probably over burned we’re still not blurring the picture we’ve still got quite nicely shaped little diamonds which are made up again not of

37:47a single pixels but multiple burn pixels ie a little line of pixels even though

37:53it’s 2 or 3 pixels only. Now I am going to try this High Definition lens on a

37:58straightforward differed random dot pattern just so that we can see what the

Transcript for Photo Laser Engraving Acrylic (Cont…)

38:05difference is but I have to say that there is no serious hint let’s go for

38:11the white area as you can see the white area now there are some dots on the edge

38:18but you know we’ve just got a solid white area there but it nicely grades

38:28out into gray and black areas the other thing to look at is we’re looking at the

38:36dot side of the picture where the laser has come from. But of course you don’t look at an acrylic picture from that side you always turn the picture over and engrave

38:45from the back so let’s just see what it looks like from the front. I think we’ve

38:52got the lettuce grid now at about the same resolution as the dot size itself

38:58and I think that can become obvious from the way that this picture is organized.

39:03Now sadly I can’t really tip the picture up so that we can see through the side of it to see what depth those dots are but those dots are basically very very

39:13shallow I wouldn’t think they’re probably more than about point one or point two deep at the most. Now that means that they

39:21will not be coloured in any way at all and what we’re actually picking up here

39:28the white is the way in which the light is being reflected off

39:33a bit like a reflector or a cat’s eye put the light in the wrong direction and

39:39the whole effect disappears. This is a graded dot pattern called Jarvis and

39:48this is pretty good when you’re working with organic materials up to about a

39:54hundred and fifty to a hundred and seventy dots per inch the problem is

40:02where we get to this area over here which is very white this is really quite

Transcript for Photo Laser Engraving Acrylic (Cont…)

40:07quite weird as I said we’ve got all this over burning that’s taken place in here

40:16where we’ve got almost like cementation between the pixels if we look at it from

40:23the other side it looks absolutely terrible. You can see how it just does

40:34all blocked out it’s not good at all

40:40Now it’s possible that maybe I could have decreased the power but it was done

40:46at the same sort of settings as the previous pictures so I don’t think I

40:51should really be changing the power a great deal because I found the right power for dots and as you can see single dots are coming out there quite nicely

41:00it’s just that where the dots have been over burnt so many times hmm

41:07it hasn’t worked whereas newsprint does. Well we’ve seen what these look like

41:17under the microscope and when you put them beside each other you can see they are chalk and cheese they’re both done at 635 dots per inch

41:27that was Jarvis and that was newsprint. Now I think it’s a very unfair test

41:35because this is done with dots and this is done with lines so I think we should

41:47go back and we should rework this one to a more sensible resolution in accordance

41:52with the dot size we’ve got a dot of point one therefore we should be using a

41:57resolution of 254 dots per inch and so what we’ll do, we’ll rerun this one and then

42:05we’ll do a comparison just before I pull it off what I’m going to do is to just

42:11come down to the bottom of the picture here and run the little test pattern again just to be sure that we’ve still got the correct settings dot dashes and

42:20dots okay let’s see what happened shall we? When

42:25we dust this off

42:31hmm well it might look half-decent on your screen but believe me in the flesh

42:41that’s pretty rubbish there’s not enough

42:49there’s not enough burning taking place in the face so let me have a look at

42:55these areas here which are the white areas and see what’s happening with my

43:01magnifying glass. Well I have to say we’ve got lots of clean individual dots on there

43:09just in these really white places yeah it hasn’t really come out all that well.

43:17The dot pattern itself is still very good but in those black areas where there should be some tone there’s no dots at all so that’s indicative of the

43:31the photo conversion. Well I’ve just been and looked at the actual pattern on the screen and there are definitely dots there, rather puzzle as to why single

43:40dots are not coming out Well the actual dot pattern itself

43:46is still performing very well and that was Jarvis let’s try the same thing with a different dithering pattern

43:55one called Atkinson well it looks like a similar story for Atkinson as well

44:04down here and a little less burning but equally well we’ve missed lots of pixels

Transcript for Photo Laser Engraving Acrylic (Cont…)

44:10across the bottom here I’m yet to be impressed looks more like a white tiger

44:24well that’s a bit better but the problem is

44:32we’ve got nothing down here there’s a bit more definition in it than that one which was done at 20% I’ll push the power up on this one to 30% and I’m

44:42still fighting to get some dots in here weird as a feature on its own it looks

44:50quite nice probably from your perspective that one looks a crisper

44:55picture this finds a much better toned picture this one has got lots of dots in

45:02it this one as I said this is nearly photo quality

45:09well it’s still not bad

45:17but it’s not to the same standard as that one what we’ve got here is our original 635 dpi newsprint after some more experiments with dotting which

45:32weren’t too successful I thought well I’ll close the loop and make sure that there’s nothing changed about the machine in other words the scan test the

45:43dots were still the same but if we look at the difference in the color of these

45:52they’re both very good I thought that that one was excellent but when I look

45:59at this one it’s even more excellent and the reason is because it’s slightly whiter and that’s all to do with the actual material itself this is an

Transcript for Photo Laser Engraving Acrylic (Cont…)

46:08extruded acrylic and this is a piece of cast acrylic well I think this

46:16session has been very successful and informative in many ways first of all it has proved that we can manufacture cost-effectively a compound lens system

46:29we don’t need to spend the silly amount of money that some companies are

46:34charging for a compound lens system we can just adapt what we’ve got it

46:41produces dots down at point 1 or less millimetres it gives us the flexibility

46:47to play with other lens configurations and there is another piece of software

46:52there called Light Burn that is absolutely designed for you guys that do

46:57lots of engraving photo engraving it’s easy to use it’s very powerful but what

47:04you’ve got to do as I think we’ve proved today is find the right dithering process for the material that you’re using

47:12we’ve only been using it today for a critic there seems to be quite an interesting difference between cast acrylic and extruded acrylic and also

47:22the choice of dithering that you use now that choice of dithering is not there on

47:29many pieces of software if you go into probably somewhere like Photoshop you get quite a few options but I don’t think I’ve seen newsprint well I know

47:39that I haven’t seen newsprint in Photoshop so the flexibility of this

47:45piece of software is absolutely amazing

47:51well I think we’ll call that the end of a very long and successful session now

47:57just remember you’ve got some homework to look up and do some reading to do so make sure you do that to completely fill in the little blank areas that I

48:07left until the next time cheerio

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Last updated April 25, 2024


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