New lens from Omtech something is Terribly Wrong

I purchased 2 new lenses from Omtech. Something is Terribly Wrong!!
In the beginning I said Mirrors a couple of times instead of Lens. Sorry about that, I blame it on the frustration.

[@SarbarMultimedia]

Hi
Auto focus is the most confusing thing to have on a laser machine because it does not contain a single brain cell so it does exactly what it's been told to do. It thinks it has focused the lens but is has no idea that you have change the lens focal distance.. I see tjat you have a C series lens tube and I know that this particular lens tube is designed to take a 2" (50.8mm) and when you place the NO3 nozzle onto the lens tube the focal point is designed to be about 5 or 6mm belo the end of the nozzle.
1) Do not worry about the lens colour. The bright yellow ones are better quality USA CVD lenses . By better quality I mean there is no optical performance difference but the brown lens is rated up to 80 watts and the yellow ones are rate to about 200 watts.
2) If you place the brown and yellow lenses side by side belly side up and look at your face in the lens it will be distorted and you may see that your head is a diffent size in each lens. In particular open your mouth wide and compare the sizes. The bigger your mouth the flatter the curved surface and thus the longer the focal length of the lens.
3) I can be certain that the brown lens is not the standa 2" (50.8mm) focal length lens the factory fits to most machines. Put your nozzle onto the lens tube and press auto focus. Now measure the gap between nozzle and material and I anticipate it will be close to 19mm. This indicates that you have a 2.5" (63.5mm) brown lens.
Its weird because the reflection form the two yellow lenses look different. Can you do the side by side test with them ot check the surface curvature. It's almost as if the yellow lens you have not tested is the same as the brown lens. However there is just one simple test you can perform to find out crudely where your focal point is and thus detemine the focal distance of the lens.
There are only limited focal lenght lenses availabler for these machines 1.5" (38.1mm), 2" (50.8mm). 2.5" (63.5mm) 3" (76.2mm) and 4" (101.6mm)
I think your brown one is 2.5" and I think your yellow one (the one you tested) is a 2" lens. Here is the VERY simple test to check which of those 5 focal distances your lenses are.
Without thr nozzle raise the table to its top position. Drop your lense tube until its about 1" clear of the table . Now drop the table about 3" and put a piece of card on the table. Press the pulse button quickly to mark the card. (it will be big) Look at the keypad and raise the table by about 10mm. move the card and repeat. Keep doing this and the burn will get smaller and smaller. At a certain point the beam will start getting bigger again. Now do fine adjustment of the table height to find the position where you can burn the smallest spot. Measure the gap between card and end of lens tube. (say 40mm). Remove the lens tube and measure how far the face of the lens is up inside the lens tube(say 11mm). Add 40 +11 = 51mm and find how close this dimension is to one of the standard focal lengths.....The 2" (50.8mm) You only need to measure within a mm or two because the match will be obvious.
OK so your new lens is different. What now? Well, you will have to learn to reset your focus switch. . Watch this video and hopefully it will explain how to do it. You will also maybe see why I have junked my auto focus because it's nothing but a pain. I always use a simple step gauge because its quicker ruclips.net/video/IDaGEu0ddrE/видео.html
If you want to make your own step gauges I can supply the DXF file. Just contact me privately with this contact form
forms.zohopublic.eu/ndeavorlimited/form/K40XtreeemLaserCutterContactRussSadler/formperma/k2Cn0QN5ChpazfTMAUw25lZ-FKpjZa96TQWHjv3ntOg
Best wishes
Russ

[@StingerLaserWorks]

Thanks for the info. I did test both new lenses and got identical results. I prefer the ramp test method for finding the correct focal distance. After doing so it showed a focal distance of 5.6mm from nozzle tip vs the 18mm for my 2” stock lens. After Omtech reviewed the results from the ramp test they sent out 2 new lenses. I will test them soon and post a video of the results.

[@RonMarshallrone]

Is it the new American Photonics lenses? I just bough the set of 4 and just curious.

[@StingerLaserWorks]

No. Just the CVD lenses.

[@n3tw0rkbl03]

its not same focus. Old lens is 63.5 and new one is 50.8