Tim,
It appears chart specifies the lens type per focal length.
38, 76, 101 = Plano Convex
50, 63, 127 = Meniscus
Sorry, wrong terminology. By standard, I meant a plano lens.
Thanks Stroonzo - I tried Googleās find on that page but didnāt realize the descriptive text was a bitmap. Ordered a couple in the the 2-in focal length for my my Nova 24.
for me a beam expander is the best solution. for my tube with a 4mm beam diameter and a Ć 2.5 beam expander, a relatively constant beam diameter of 10.5 to 11mm @ the lens.
the less the beam expands, the less the DOF influences when the head moves left and right.
The larger the beam diameter on the lens, the smaller the focus point.
10.5mm is a very good improvement in the size of the focus point
100W.
It will engrave, it just doesnāt look as good as what people with lower power lasers produce. Lowest power before the laser stop firing (8%) is too much power, and using higher scanning speeds to compensate is too fast for high detail (anything above 100mm/s).
Looks like I got a fake lens through Amazon. I guess thatās what we have to deal with more and more often. Working on the refundā¦
Sorry @Stroonzo!
The sad part is that they probably got away with it for a while with other users not as savvy as @Stroonzo
So sorry friend 
Hey Jeffā¦ that is a bummer.
But what is wrong with the āfakeā lens?
Well, for starters the anti reflective coating of ZnSe lenses is that of radio active Thorium. 
So buying from a certified and legitimate source may be comforting. Despite itās negligible content under normal circumstances, shall I risk unregulated radioactive components?
Also, quality. āFinished optics manufacturing requires unique techniques coupled with precision-machining and fabrication. II-VIās Saxonburg plant has provided optical fabrication capabilities to our customers since 1971. On average, our operators have 15 years of optical fabrication experience. Although we specialize in build-to-print work, our state-of-the-art equipment enables production ranging from prototypes to OEM products.ā
http://www.iiviinfrared.com/pdfs/II-VI_InfraredMaterials2009-04a.pdf
hahaha ā¦ butā¦ in my defenceā¦ I couldnāt see the quality in the picture as clear as your picture!
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Can you provide a solid link to replace the factory lense in a 60w OMTech laser ? I canāt seem to find what size, etc lense i currently have
man Iām hurtingā¦ I canāt get my laser cutting again, Its driving me insane and iāve got so many orders backing up. I REALLY appreciate any and all help, Thank you so much
if my lense is 17.75mm Should I go with an 18mm ?
Ya, and unfortunately we only caryy 20mm lens diameter. Try Cloudraylaser.com
Right now, it sounds like you need a lens / your machine is down. Go to Amazon, find an 18mm lens in the FL you want and order it Prime. This will get you back to work.
While ordering (today), you might as well just give cloudray a try and order a couple of those USA CVD ZnSe lenses.
Lenses are coated either by way of Physical Vapor Deposition (PVD) or Chemical Vapor Deposition (CVD). You want CVD.
I called the support line on the website, They had me doing all kinds of stuff from stuffing padding under the tube to help center it on mirror 1. They spent a good 1.5 hours with me. I canāt complain about support. I did order a new lens to get to me tomorrow & will order better ones as well in the meantime.
Im going to order a better tube & adjusting clamps as well. Not sure on the tube type if you have any suggestions iād really appreciate it.
Im about to test my cutting settings to see if they help.
Maybe itās just my Chrome browser, but all of your Ini-Infrared links take me to the company home page and I find it confusing trying pick out the right section to browse there lenses for my Thunderlaser. Is there a search term that would help me find the right web page(s)?
Got my 2.5 lens in today, HOLY COW what a difference. 1 pass cutting acrylic again at a higher height no less. Testing it now with my other things for orders, The more complex the shape i notice it needs an extra pass ( for now ) but i see the difference, Iām ordering new tube clamps & mirrors along with a few cloud ray lenses, Do you recommend 2.5ās or any other ?