View Full Version : Lens focal length

Glen Peters
10-22-2004, 4:19 PM
I have a Pinnacle M-25 with a 2 inch lens. I can purchase a 1.5 inch lens to use on my laser and understand that the shorter focal length has a smaller spot size and will produce more detail.
Does anyone use anything other than the standard 2 inch lens? If so, is the increase in engraving detail worth the cost of the lens (not cheap!!)?
The material I was thinking of using the 1.5 inch lens with would be marble/granite, metals and tile with thermark or cermark.


Chuck Burke
10-22-2004, 8:45 PM
Hi Glen,
I have the same machine. How do you like yours?
I don't have an answer for you regarding the lens, but I did try some granite with my machine and the 2" lens and it was "acceptable" in detail. I believe this was due to the granite itself. Note exactly the best for laser engraving I am told. I am going to try some marble in the next day or two when I get a chance and I will let you know how it works out.
I did get the 4" lens though so I can do champagne flutes, but as of yet, I have not used it.
Anyway, good luck. There are a lot of forums out there and a lot of great information.

Chuck Burke
Pacific LaZer Works
Woodinville WA.

Rodne Gold
10-23-2004, 5:15 AM
I use 1.5 , 2" and 4" lenses. They are expensive and unless you have specific applications the 2" lens will do fine.

It all boils down to power density and divergence and convergence. In essence only at the focal point of a lens will there be the maximum power density , the beam looks almost like an hourglass , the focal point is the thin waist. The shorter the lens , the "shorter" the hourglass.
The spot size decreases with the decrease in the focal length of a lens , IE a smaller spot size cointains more energy for that area and thus "concentrates" the beam
Essentially a 1.5 inch lens will allow more precise engraving , however that depends on the item being engraved. If for example engraving wood , where there is a large heat affected zone around the vaporised section , having an exteremely small spot size will not help at all and can "overburn" the wood.
Small spot size lenses will show up any imperfections in a motion system and can highlight banding etc. The other "downside" is that it cannot cut thick stuff well and any variation in height of material will be far more critical than with another longer lens. It also is very close to the object , so fumes , flaming etc can damage the lens and head assembly or make it dirty much quicker.
Conversely a 4" lens will NOT produce crisp engraving on small letters etc. However it will give clearance for some objects , it will also reduce smoke deposit etc on a lens as its further away and albeit the power density is less due to its increased spot size , the "hourglass" is stretched , so it maintains a cuttable power density much further away from the focal point in both directions. IE good for cutting thicker stuff.
It's larger spot size also enables you to use less DPI and thus engrave large areas a a lot faster with a smoother effect if the ultimate "sharpness" is not required.
We have very specific applications which require various lenses , like ablating masks for acid etching where the small spot size of a 1.5 " lens makes for extremely sharp and well defined detail especially if doing 1/2 tone work. We use brass or stianless steel as substrates so they ARE dead flat.
4" lenses are great for high volume 8-10mm thick acrylic cutting etc - the 4" lens is more a cutting lens than an engraving one, the kerf width is bigger resulting in less re-melting together of cut surfaces and the sides of the cut are straighter. Often a particular lens cant be used with objects that have height etc , for example using a 4" lens will reduce your table to head clearanc by 2" and often the focus probe cant be used with a 1.5" lens as it slams into the object. Even the nose cone can interfere with 1.5" lenses.
I don't think that the expense of a lens is worth it unless you do run into problems with the 2".
In terms of glass and stone engraving , what happens is the localised "hit" of heat fractures and "chips" the substrate , thus short focal length lenses will tend to damage the substrate to some extent or not give a smooth effect. The increase in detail of a 1.5" vs a 2" lens might not at all be apparent and indeed might give worse results.

Rodne Gold
10-23-2004, 5:19 AM
Just another point , in the Mercury , I forget which , but I think the 1.5" goes in a different slot in the head and thus changes alignment somewhat as well. If you upgrade to an explorer , you have to pop the lens out of the mercurys square housing and partially dissasmble the current lens holder to use the other focal points.
Rodney Gold

Glen Peters
10-23-2004, 10:33 AM
Chuck- I've had my machine about 1.5 yrs and have been very satisfied with it. It has done everything I have asked it to do but as the saying goes "garbage in, garbage out". Think this is true with any computer driven tehnology. Tech support has been great. Mechanically, Auto Focus went out but have found that to be no big deal. Did get it fixed but started using manual focus which dosen't take much time. Auto focus on my machine did drift out over time and had to be reset. With manual focus you don't have to worry about it being off.


"They are expensive and unless you have specific applications the 2" lens will do fine."

That is the same conclusion I had arrived at but was just wondering if I was over looking something. Thanks for all the input. Never can learn too much.


George M. Perzel
10-23-2004, 11:05 AM
Hi Glen;
I also have a LaserPro- a 60watt unit and have used both the 2" and 4" lens. Rodney's explanation says it all precisely and consisely-best explanation of subject that I have seen.
Everyone I have talked to regarding Laserpro/Pinnacle shares belief that 1.5" lens is not worth the cost.
I am curious, however, whether anyone has found a source for laser lenses and mirrors other than the OEM?
George M. Perzel

Glen Peters
10-23-2004, 11:57 AM
Hi George

I only have the 2" lense and can't justify the cost for an additional focal lengths at this time.

I did a quick google on "laser lense" and got this hit.


I have a dialup connection and haven't checked out what they have but the first page looks promising!! i.e. you will find information on our OEM-quality replacement CO2 laser optics (http://www.iiviinfrared.com/replacement.html)

Rodne Gold
10-23-2004, 1:37 PM
Yes , that lens supplier will have replacement optics , good find:)
I cant see how your autofocus went out, its just a microswitch? Perhaps it slipped in the collar.
One thing I found dreadful about the Mercury and the explorer is the awful rotary attachment. We have converted ours with various heads , one with replaceable cones , another with centering jaws like a lathe and the other with a cone and jaws. and a tilt adjustment. Even so , it is not intuitive to use it. Other mods are the fitting of an internal light.

Glen Peters
10-23-2004, 4:15 PM
The ribbon cable to the microswitch on the lens carrier had a broken lead somewhere in its length. With tech support's help we checked all connections and finally found that auto focus would work on the right half of the table but not on the left half. Apparently when the lens carrier was to the right the ribbon cable was flat and the broken ends touched, when near the left side the cable was bent separating the broken wire and opening the circuit.

I was thinking of some sort of light in the cabinet also. What sort of light did you use and where did you mount it? I was thinking maybe a Xenon puck light would work.

My rotary fixture has seen no use. Just from looking at it I would think that it would be difficult to center something so it would't wobble on its axis.

Rodne Gold
10-24-2004, 4:47 PM
Ah , yes , I remember we had problems with ours , fitted a twisted copper pair instead. We just put a flourescent at the back.
The rotary actually works ok , laserprousa have great instructions for using it , the manual is unclear. They also got a nice doc on alighment , a DIY thing.

Kevin Huffman
11-01-2004, 11:46 AM
Hey Guys,
I am sorry I missed this whole post. Alot was said and I didn't get to comment on any of it. LoL

If you are looking for a more up to date manual you can visit.
http://www.laserpin.com/index_LI2.html .
Under the Setup section there is a link to your newest manual. It will continually be updated so look on there often to find the latest one.

If you are looking for beam alignment help, there is a couple of videos which show you how to test your laser to see if it is aligned and how to adjust it if it isn't in alignment. Just look under the Imaging Information section for those.

Chuck Burke,
Give that manual about 1 more week, there will be a awsome section on the rotary attachement. We have had a lot of people displeased with this part of the manual we are working on it non stop right now. It should be posted on the web in about a week.