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Jonathan Bowen
07-11-2014, 5:14 PM
So I've noticed that my lens is getting rather scratched up and may be causing some of the issues that I'm still dealing with from the move and the upgrade to 60 watts. At this point I don't think I need to upgrade to large optics and I'm not sure if I want to go ahead and do the mirrors as well. I've switched to an oil based compressor and have had several issues with small drops of oil making it onto the lens. I have a filter in place that traps water fine but the oil seems to be making its way into the system. Do I need another kind of filter to trap the oil? I want to fix that before I get the new optics.

I'm going to measure the lens again but I think it's 18mm and its 2" focal length if I remember correctly. I'd check but Hurricane is gone so I'd have to get into my original documents to see what it was installed with. I know focal length has something to do with kerf sizes but not sure about the coatings and the types. Lightobject lists several 18mm ZnSe lasers of different qualities and a few GaAs. My beam combiner is currently not installed so not really worried about that. It's another major project to get it to work. The new tube has the lenses so far out of original specs that I can't get the red laser beam to hit it correctly without making a new bracket.

Does a higher power rating on the lens mean it will work better at 60W or does the quality only matter when the wattage gets higher?

Thanks!

Brian R Cain
07-11-2014, 6:10 PM
Just get yourself an oil-free compressor and be done with it. It isn't worth the grief.

I can't speak for Chinese machines, but the US ones use the same lenses for all power options. What you have to remember is that a dirty lens is inefficient at transferring the power to the job. So instead of heating the material, it gets hot itself and then gets damaged. The more power you subject a dirty lens to, the hotter it will get and the more quickly damaged.

I haven't thought about this before, but it occurs to me now that a scratched lens will probably be refracting the laser back into itself and cause it to get hotter than it would normally. Also possibly cause interference with the beam. I don't know, I'm not much of an expert with optics above what they told me at school and asking myself practical questions when things don't work as they ought.

All I can say with regard to cheap lenses is that they're cheap for a reason and the likelihood is they're not as good. When I was in my 20s I bought a Nikon SLR camera and a couple of lenses. The quality of the snaps they gave me were great, but as I became more interested in photography I wanted other lenses. I'm sorry to tell you than when I was in my 20s with a kid to feed and a mortgage to pay on a meagre salary, I couldn't run to a long Nikon lens and opted for a cheaper alternative. A total waste of money it turned out to be too. Never had a decent picture out of it and gave up on it after a couple of rolls of film. I could put the 100 quid the lens cost me down to experience, but I wasn't about to continue wasting money on having film developed and photos destined for the trash can.

I can't see why it will be any different with laser lenses unless a miracle has happened and if it had, you'd expect the major manufacturers to be using it to competitive advantage.

Dan Hintz
07-11-2014, 8:07 PM
The lens quality issue has been beaten to death in the past. Sure, cheap $5 lenses may or may not be worth more than the shipping material they're enclosed in, but generally by the time you get to the $30ish mark it's a reasonably decent lens for the systems they are installed in... certainly for the beam quality out of a Chinese glass tube. I would not be content with a $30 lens in a $100k machine, but at that level of machine, a high-spec lens gains you significantly more than a lower-spec lens on a $5k machine.

Michael Reilly
07-12-2014, 12:09 AM
Laser lenses are made from a material that seems to be manufactured in the US. So even if you buy the lens from China, the material was made here and shipped over there for grinding. As a result, the prices didn't seem much better. My Trotec replacement lens came in a II.IV case so I bought from them before realizing they're very expensive. I initially used ClearBeam Corp which makes Epilog's lenses. But someone on the Epilog forum turned me on to American Photonics which has been good so far and by far the cheapest. I pay $185 for a 1" diameter coated lens that would be $300+ at II.IV.

Anytime you replace a lens, be sure to do a focus test and see if you need to adjust your focus guide. Even identical lenses from the same supplier seem to vary slightly.

Brian, the differences in lens quality for cameras is a bit of a different situation. Camera lenses often have multiple stacked elements. These exist to allow you to zoom, as well as to focus the image onto a relatively large sensor/film frame compared to the lens diameter. Poor lenses can have problems at the edges of the sensor with uneven light levels, they can have issues with focus across the sensor, etc. In our case, we need only take a pencil diameter beam and focus it to as fine a spot as possible within a prescribed distance (focal length). We commonly use plano convex lenses, they are rounded on top and flat on the bottom. These give a good spot, but the refraction of light through the lens material means not all of the beam is successfully focused on one spot. For that, they have negative meniscus lenses which are ground on both sides for the purpose of addressing the refractive error. It can focus more power on a smaller spot, but at the cost of less depth of field (area in focus.) So on materials that might have warp or vary in thickness, such a lens will get out of focus more easily.

Beam combiners are used mostly for allowing a laser pointer to share the beam path with the CO2 laser for the purpose of sighting the cut area. When we got our Vytek laser, it was recommended that we go without that because any optic added to the beam path like that is likely to reduce the beam quality, if only slightly. It's kind of a pain without though. We've been forced to develop other techniques for alignment.

Robert Tepper
07-12-2014, 12:43 AM
Try Laser Research Optics. I have used them twice and I have been very satisfied with their work. I sent back my cracked lens in the holder. They replaced the lens and properly lined it up. They can be found on Google. It takes about 3 weeks to get your order returned, so plan your time properly. The price was very reasonable as compared to purchasing a new lens from the manufacturer.

Just my opinion,
Robert

Kev Williams
07-12-2014, 2:16 AM
For the life of me, I can't figure out what I could possibly gain by using an expensive lens over whatever I'm using now...

My 17 year old Optima (ULS) continues to engrave simply beautiful itty-bitty .06" text on itty-bitty plates for a regular customer, and it does it with the original 17 year old beat up, pitted & scratched lens. Original mirrors too...

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I put in a borrowed nearly-new lens not long ago, checked the results of both with a 30x loupe, there was no discernible difference in the engraving quality.

Right now the new $60 plain jane 2" lens in my Triumph is engraving an I-Ching circle into a 24" diameter alter table top, it's cutting 1/8" deep running 220mm/second, not sure it would go any deeper or faster with a $600 lens ;)

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Dan Hintz
07-12-2014, 7:54 AM
For the life of me, I can't figure out what I could possibly gain by using an expensive lens over whatever I'm using now...

My 17 year old Optima (ULS) continues to engrave simply beautiful itty-bitty .06" text on itty-bitty plates for a regular customer, and it does it with the original 17 year old beat up, pitted & scratched lens. Original mirrors too...

292892

I put in a borrowed nearly-new lens not long ago, checked the results of both with a 30x loupe, there was no discernible difference in the engraving quality.

Normally I'd agree with you on the sentiment, Kev, but it pains me to see that lens. There's more to a lens than just the quality of the final engraving... the AR coating on that guy is destroyed. Any signal reflected back to your laser cartridge is slowly beating it up, so it's in your best interest to replace that guy.

Ernest Martin
07-12-2014, 8:57 AM
For the life of me, I can't figure out what I could possibly gain by using an expensive lens over whatever I'm using now...

My 17 year old Optima (ULS) continues to engrave simply beautiful itty-bitty .06" text on itty-bitty plates for a regular customer, and it does it with the original 17 year old beat up, pitted & scratched lens. Original mirrors too...

292892

I put in a borrowed nearly-new lens not long ago, checked the results of both with a 30x loupe, there was no discernible difference in the engraving quality.




I'm definitely not an optics specialist, but I would think that a lens like this would take more power to produce the same amount of engraving as a good quality lens. Every scratch mark I would assume would direct the beam a little different.

On a different note we purchased some lens off of ebay several years ago I have no idea what brand but they were inexpensive. We put those in and noticed a difference in the amount of power it took to cut or engrave so we switched back to our old lens this was on a 35 watt Epilog.

Dan Hintz
07-12-2014, 10:19 AM
Yes and no... with the low powers we make, scratches will lower the power to such a small degree it is likely within the power fluctuations of a tube as it changes temp over use (a Watt or two). Still, it leads to minor inconsistencies that over time will add up... half a Watt here, quarter Watt there... eventually your initial settings need a bit of tweaking.

I'm all for keeping a machine in good shape, but not overdoing it to the point of being anal (and for an anal person like me, that's saying something). A few micro-scratches wouldn't concern me, but that lens above would be replaced in a heartbeat. Whatever level you're comfortable with.

Kev Williams
07-12-2014, 11:24 AM
I definitely agree I should, and will, change the lens- taking these pics last night was the first time I'd looked at it closely in quite awhile. However, my point that this beat up lens engraves almost exactly the same as a new version of the same lens, stands. Since I'm not doing eye surgery with my lasers, the cheapest lens available will be fine by me!
;)
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Dan Hintz
07-12-2014, 12:19 PM
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Looks good to me... but search out some nail clippers and cuticle care products ;) :p

Scott Shepherd
07-12-2014, 12:24 PM
Dan, that's what the hands of people who work for a living look like, just for reference :D

Dan Hintz
07-12-2014, 12:28 PM
Dan, that's what the hands of people who work for a living look like, just for reference :D

"Hey, would someone mind removing this knife in my back?"

"Good... Now back to work, minions!"

:p

Scott Shepherd
07-12-2014, 12:50 PM
Hehehe, sorry, couldn't resist :p

Kev Williams
07-14-2014, 3:21 PM
Looks good to me... but search out some nail clippers and cuticle care products ;) :p If I could find a cure for the exema that's been plaguing my hands for the past 9 years, they wouldn't look like that!