What is the Secret to Using the 1.5 Lens?

[Tim Bateson]

OK, this should be simple for someone to answer. For me, It's been a long week and my brain is shutting down for the night.

Just got a new 1.5 lens. I've had a lot of requests for very small items that the 2.0 just cannot produce in detail. Now, I've tried a dozen different settings and I do get great detail on the back side, but the front is either burned too deep - loss of detail or it looks good, but I didn't cut all of the way through.

I'm practicing with vector cuts on 1/8 birch ply. I'm surprised that with the lens being closer to the work area, the focus is the same as with the 2.0. What am I missing?

[Steve Clarkson]

Tim, I have a 1.5" lens that I don't use much. As far as I know, the focus shouldn't be the same......it should be 1.5" off the material, not 2"...maybe that's your problem? I also found it was alot more powerful than the 2".......so I have to back off on my power settings a bit.

What I've always been curious about is if the beam width is smaller (if a 2" lens is .003 then the 1.5" might be .002.....just a guess), how does the laser know that there is a smaller lens installed (thus smaller beam size) when engraving say a 1"x1" black square? Wouldn't it take more left/right rows to engrave the same size box?

[Craig Matheny]

Steve is correct you need to be 1.5" away from the material just like with a 4" lens you need to be 4" away.
By the way when you get it cutting let us know if it is faster on the birch..

[Richard Rumancik]

. . . . I do get great detail on the back side, but the front is either burned too deep - loss of detail or it looks good, but I didn't cut all of the way through.

I'm practicing with vector cuts on 1/8 birch ply. I'm surprised that with the lens being closer to the work area, the focus is the same as with the 2.0. What am I missing?

Are you saying that you did not change the focal length when you changed lenses? I don't have an Epilog but if I understand the construction correctly the 1.5" lens goes in the same "slot" as the 2" lens. Which means that you need to change focus appropriately. It seems to me you are out of focus.

(The GCC Mercury and perhaps some other GCCs are a bit different as there are two lens slots situuated .50" apart. So in this case you use the same focus tool for both the 1.5" and 2.0" lens. But I don't think the Epilogs have this construction.)

One other comment - 1/8" baltic birch is really pushing it for a 1.50" lens. You might be able to get through but I don't think you will see throughput. The 1.50 is good for thin materials and fine engraving, but not for cutting materials above .10" or so) If you try to cut BB with the 1.50 I'd probably try to focus into the material a bit and see if you can get decent results.

[john banks]

Interesting. We cut 0.37" ply with our 1.5" lens for the sign for our house because at the time we got much more airflow with the shorter lens before we got the cone extension. Now we would use 3" for the same and have received 4" to try. Between 1.5 and 3" we straighten the kerf and lose a little definition on engraving but either lens will do most things. We use 3" for engraving for uneven materials to keep focus.

We don't have to adjust speed between lenses and focus on the surface for best results both cutting and engraving. We chose our own focal distance based on results.

It is a Chinese 100W machine though, so apples to oranges.

[Scott Shepherd]

The "working range" of the 2" lens isn't much more than 1/8". The range on the 1.5 is probably about .060" or so. So cutting something 1/8" thick is really pushing it, unless it's acrylic. You can certain cut thicker, but you really start to see the angle on the edges, especially with the mid range power, like 45W or so.

You'll get no direct benefit without changing the resolution you send it over at. If you're sending it at too low a DPI (the same as sending it over with a 2.0 lens), you're just running a smaller beam over the same path, with won't yield better results. If you want to see a 1.5 lens shine, put it in focus (which you haven't), and then send it over at a high DPI.

[Mike Null]

My theory is that the 1.5" lens is for fine engraving not cutting. Even there you have to be careful not to overpower the job or you will lose detail.

Focus is all important.

[Craig Matheny]

The "working range" of the 2" lens isn't much more than 1/8". The range on the 1.5 is probably about .060" or so. So cutting something 1/8" thick is really pushing it, unless it's acrylic. You can certain cut thicker, but you really start to see the angle on the edges, especially with the mid range power, like 45W or so.


Scott I have a 45 watt Epilog 2" lens cut 1/8" Baltic Birch all day long and 1/4" doug fir with no issues. yes the speed on the 1/4" is a 1/3 slower but clean no char.

[Richard Rumancik]

A 1.5" FL lens will vector cut fine, it is just that you can't go too thick. It is great for films, Rowmark sheet (.020-.060 range), veneer, thin aircraft plywood, etc.

I suppose if you put 100 watts behind it, it will do things that a 30 watt won't. But it will probably generate a wider kerf as the lens will be out of focus as it exits the material. (Or you can focus mid-material so it is out of focus at entry and exit, and thereby split the difference.)

The depth-of-field of a lens is a definition rather than a law of physics. You can certainly cut materials beyond what is considered the depth-of-field range of a lens (by going slower or increasing power) but you will get increasingly poorer cut quality. It is more of a rule of thumb to decide on an appropriate lens for a job. But there is no harm in trying to push the limit beyond the stated depth of field. If it works, it works.

[Rodne Gold]

I seem to remember reading that depth of focus of a laser is defined from + and - 1.4 x the spot size ( http://www.buildlog.net/cnc_laser/laser_calcs.htm ) but as you say , energy density might be sufficient to do the job of cutting etc way beyond that.
We use 40mm lenses in the higher powered machines and they do the same job as my 50mm lenses in lower powered ones thickness cutting wise but also give finer engraving. Once you start cutting , the 2 lenses have more or less the same kerf width - the extra DOF the 40mm is asked to produce to cut the same thickness kinda negates it's smaller spot size compared to the 50mm.

[Michael Hunter]

I think that what Tim meant in his original post was that the focus gauge/autofocus is exactly the same with the 1.5" lens and the 2" lens.
That is OK, since on the Epilog the lenses are mounted in their holders at different heights to account for their focal lengths.

What might throw things off is that if the focus gauge is a bit off for the 2" lens, then the error will be much worse for the 1.5 lens with its shorter depth of focus.
Worth checking that the focus is true using a bit of scrap anodised aluminium.

Scott's point is valid - if you normally run the 2" lens at 300dpi, you should be selecting 400 or 600dpi to get the benefit of the smaller spot of the 1.5.

[Tim Bateson]

Thanks for all the input. I had expected more of us using both the 2.0 and 1.5 lens on a regular basis. I have a lot of sampling/practice ahead of me to master the best techniques for the 1.5. I'd like to hear from some of the folks here who cut out miniature items.

[Scott Shepherd]

Scott I have a 45 watt Epilog 2" lens cut 1/8" Baltic Birch all day long and 1/4" doug fir with no issues. yes the speed on the 1/4" is a 1/3 slower but clean no char.

I'm not suggesting you can't of shouldn't cut items thicker than the working range of the lens. But the purpose of the 1.5 lens is to get a thinner kerf. If you go thicker, the kerf is so thick at the bottom, you wasted the use of the 1.5 lens.

You MUST increase the DPI if you want to see the fine detail the smaller lens will shine at. You don't have to, but you won't see the benefits like you'd expect if you don't.

[David Fairfield]

Hi Tim

Most of my work is miniature, or extreme miniature. However, I rarely find use for my 1.5" lens. The 2" lens does just about everything I need, mostly at 600 dpi. I can go a little finer with the 1.5" lens at 1200 dpi but most of the time, the difference is not worth swapping the lens out, and the additional machine time needed to run at 1200 dpi. I find the difference is only visible under magnification.

The 1.5" requires a more precise focus, so when I do use it, I make sure I'm pulling a good vacuum on the vector grid to hold the material flat. If I used it more often, I would make or buy another manual focus gauge specifically for it.

If you aren't getting super fine cuts and engraving with your 2" lens, take it out and make sure its clean and like new. Also run a diagnostic with both lenses to make sure your focus is on target. My laser required a focus adjustment after a few years of regular use.

Dave

[Craig Matheny]

I think that what Tim meant in his original post was that the focus gauge/autofocus is exactly the same with the 1.5" lens and the 2" lens.
That is OK, since on the Epilog the lenses are mounted in their holders at different heights to account for their focal lengths.

What might throw things off is that if the focus gauge is a bit off for the 2" lens, then the error will be much worse for the 1.5 lens with its shorter depth of focus.


I don't know about your machine but my Epilog does not have multiple slots or mounting locations for the lens. Maybe if you by the complete assembly you get a thicker holder? but on mine the lens goes into the same holder and location for any focal lenght and then you adgust the distance to the materil based on the lens.

[Frank Corker]

http://www.epiloglaser.com/tl_focus_lens_101.htm

[Michael Hunter]

Craig ...

Here is the Epilog manual page for my machine. I would assume that they have done something similar for other machines that can accept a range of focal lengths.

As you can see from the pictures, it is the lens position within the holder that changes, rather than the position of the holder within the machine.

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[David Fairfield]

That Epilog diagram, and instructions I got with my 1.5" lens, were misleading. My 1.5 lens does not focus at the same distance as the 2" lens, I need to drop the table 7 clicks.

If there is any doubt about where the focal points are for your lenses, trial and error on scrap material is a simple way to determine them. I don't trust the autofocus feature and removed it not long after I got my machine.

Dave

[Brad Ports]

Using my ULS 30 watt, I cut with my 1.5 all the time. What I have found out is that to get a great cut you need to slow it down and lower the power. for 1/4" baltic birch I use 45% power and 1.2 to 1.3 speed. for 1/8" same power but 1.6 to 1.8 speed. I can cut 3/8-7/16"solid maple using this lense with a single pass. I do alot of inlay work using 1/8" exotic hardwoods and have found that I sometimes have to sand the pieces to get them to fit. Kirf is that small. I can get almost no gap without having to change size of piece in Coreldraw. I also get a cleaner edge with the 1.5 lense than the 2.0. I actually think the 2.0 engraves better because it overlaps better due to the beam size. Here is an example of what I do with my 1.5


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[Kay Bengtson]

I bought a used ULS 25ER and it came with what was labeled as a 2.0" lens. It was a bear to get proper cuts with the system which was probably why the fellow sold it to me in the first place. Well, I finally made up a focus test by making a series of parallel lines at 1/8" intervals and etched a piece of balsa tipped at a precise angle. The ends lines came out really wide as the beam was clearly out of focus there and in the middle they narrowed where I thought the focus would be but the center of the sharp area was offset to the higher side. When I did the geometry, I discovered that my so-called 2.0" lens was actually focusing at 1.5" . Now, I know it is best to use anodized aluminum for precise focusing tests but my simple scheme did ferret out this problem very well. So I reset my focusing tool to the get the 1.5" focus from the bottom of the lens to the work and bingo, it cut great. I later bought a new 2.0" lens and liked the cutting results even better. So it could be that your lens is mislabeled too.

Kay

[Michael Hunter]

A further thought ...

My machine was supplied with a 2" lens.

I do quite a lot of black anodised aluminium.
I have to run this at 1200 dpi : if I run it at a lower resolution I get grey bands in the engraving.
This means that the **effective** spot size of my 2" lens is less than 0.001", so I have never felt the need for a 1.5" lens.

(What would sometimes be useful is a 4" lens, so that I could engrave into machined pockets in objects without the autofocus plunger and air-assist pipe running into the work).

[Tim Bateson]

... My 1.5 lens does not focus at the same distance as the 2" lens, I need to drop the table 7 clicks...

Bingo! Same here. Testing on anodized aluminum I got the best results from setting with the manual gauge then 7 clicks down. Not 10 down not 5 down, but 7 was the best result. This lens came with another manual gauge tool. It's adjustable, so I am setting it to the proper height and marking it for 1.5 only.

NOTE: The new gauge is already adjusted to the appropriate height. Just looking at the two gauges it's not real noticeable that one is set 1/16 or so longer than the other. They are now both marked to avoid any future confusion.

[Rodne Gold]

We check focus with ANY lens change - even a 2" to a new 2" , it's always out compared to Auto focus and even manual focus. With the 1.5mm , checking focus is critical as even a 1/25th " error can make a big difference.

Michael , As to using 1200 DPI to avoid banding , well that's an issue with your laser motion system and overlaps or something else and not lens native resolution..a 1.5" lens will not achieve a spot size of less than 0.003" , and that equates to 300 dpi - running at 1200 or so will not actually give better resolution than 300 dpi in photo engraving relative to SPOT SIZE... It will give different results in terms of dot gain and overlap and solid/bitmap fills etc. The practical/theoretical smallest spot size the laser will do is actually 0.003" or so , you can never get an effective 0.001" spot regardless of lens used. A 4" lens is pretty useless for engraving anything with fine detail or letters smaller than lets say , 1/5" , it engraves small stuff terribly (and unless you got a ton of power , won't cut thicker stuff better - its actually a lot worse with lets say a 30w laser than a 2" due to energy density).

[Scott Shepherd]

The practical/theoretical smallest spot size the laser will do is actually 0.003" or so , you can never get an effective 0.001" spot regardless of lens used.

I don't agree with that. The HPDFO lens on the Universal is .001" (or a little less). I've seen insanely detailed work from it.

[Ross Moshinsky]

A further thought ...

My machine was supplied with a 2" lens.

I do quite a lot of black anodised aluminium.
I have to run this at 1200 dpi : if I run it at a lower resolution I get grey bands in the engraving.
This means that the **effective** spot size of my 2" lens is less than 0.001", so I have never felt the need for a 1.5" lens.

(What would sometimes be useful is a 4" lens, so that I could engrave into machined pockets in objects without the autofocus plunger and air-assist pipe running into the work).

I've studied and compared resolutions quite a bit because the dpi is directly proportional to engraving time. The only time I've found that 500/600 dpi didn't create as good of results as 1000dpi was on glass. Glass we engrave at 800dpi (I believe) with wet paper. The only other time we really engrave at less than 500dpi is for photos (normally at 300-500dpi) or trophy plates (400dpi, the 20% time difference adds up quickly).

As Rodney has suggested, I'd look at the laser's motion system and the material. My guess is you have a bad bearing.

[Richard Rumancik]

. . .Most of my work is miniature, or extreme miniature. However, I rarely find use for my 1.5" lens. The 2" lens does just about everything I need, mostly at 600 dpi. I can go a little finer with the 1.5" lens at 1200 dpi but most of the time, the difference is not worth swapping the lens out, and the additional machine time needed to run at 1200 dpi. I find the difference is only visible under magnification.

Dave, I have seen some of your work and appreciate the level of detail you achieve. So with all due respect to the quality of your work, there is something puzzling since you don't see an advantage to the use of the 1.50" lens for miniature work. You are referring to marking above, but you should see a difference in vector cutting with a very tiny kerf which should be an advantage in miniature work. Some years ago I was cutting "miniature" doll house furniture kits (this is not the stuff kids play with; this is for "senior" ladies who have this as a hobby.) I can't remember the scale but I cut it all with a 1.50" lens from 1/16 basswood. I still did kerf compensation on my outlines but I would have struggled with this job using a 2" lens.

I make Rowmark tags and operator control panels for electronic equipment from .020" sheet and I always use the 1.50 lens as I can get much better text and it cuts the sheet fine.

A 2" lens will have approx a .005" spot so using 600 dpi the dots will be .0017" apart. Those are big dots relative to the pitch (large amount of overlap). If I use a 1.5" lens the spot size is more like .003" so with 600 dpi which to me makes for a better image. In fact I don't even need to go as high as 600 to get a clear mark. The smaller spot size reduces the jaggies on the outline of an image as well.

Using the 1.5" at 1200 is probably overkill for most things. The dot size is ~.003 and the pitch is .0008" so you are again getting a lot of overlap. I don't think an overlap beyond half of the spot size buys you anything.

You seem to be satisfied with what you are getting but for the type of work you do I'd suggest you explore it a bit more. Maybe when you go to a show ask for a demo of 2" lens vs. 1.5" (take a file with you) and compare it to what you are getting.

[David Fairfield]

Hi Richard,

Thanks I'll keep it in mind next time I go really small on something or I'm experimenting. So far, the 1.5" lens doesn't really have a great advantage for me either vectoring or engraving. When vector cutting, with either lens, I compensate for the kerf in the graphic, so the finished parts are the same for my purposes.

I found the only real advantage to the 1.5" is engraving extremely fine print, which is more or less a gag, as it can't be read, and is always overlooked, without magnification. Any other advantages are, for me, outweighed by the inconvenience of swapping the lenses, and more importantly, the 1.5" lens' sensitivity to focal distance, which is effected by warp to the material or if an overlooked chad is left under the material, the table is a little bit off, etc. Things I don't need to be concerned about with the 2" lens.

I did notice when comparing things I made when the machine was new, with things made more recently, that my 2" lens kerf had widened somewhat. So I recalibrated the focus, cleaned all the optics according to Epilog's guide, and that helped get better performance with the 2" lens. So I'd recommend a diagnostic and cleaning, before buying the 1.5" lens, as it may not be necessary.

Dave

[David Fairfield]

PS I did some experimenting last night with the 1.5" vs the 2" since Richard's, and others' posts made me curious. With engraving micro sized print, I found little difference between the two lenses at 600 dpi. Only at 1200 was the better sharpness of the 1.5" apparent. I guess different systems produce different results, but thats how it is with mine.

Dave