Which way is your Focal Lens installed

[Larry Robinson]

Curious as to how everyone has their Focal Lenses installed. I have a drawing below showing two different diagrams. The Mfg of my Laser recommends Diagram 2 convex side down. However, I have notice drawings of other Mfg, showing Diagram 1 convex side up.

I have installed the Lens both ways and notice that the Laser cuts better with the Focal Lens installed as shown in Diagram 1. I did have to change the Focal length down to get the better cut.

[Randy Digby]

My salesman showed me a little trick to getting mine in correctly. I hold the lens beside the holder and look at it (head about two feet away). If I can see my reflection, it is correct. If not, I have the wrong side up. Don't know if this works for all or not.

[Scott Challoner]

My salesman showed me a little trick to getting mine in correctly. I hold the lens beside the holder and look at it (head about two feet away). If I can see my reflection, it is correct. If not, I have the wrong side up. Don't know if this works for all or not.

My Laserpro rep told me the same thing, so it must work for all.

[Albert Nix]

On my MII the lense will not go in the holder up side down???

[Dan Hintz]

Randy/Scott,

That should work with the typical lens seen with most of your systems (but not all, as some systems do not use the typical Plano-Convex).



Larry,

Your diagrams show a positive meniscus lens... if that's what you have, Diagram 1 is the correct orientation (the less curved side towards the substrate). If it's a Plano-Convex, flat side towards substrate.

[Larry Robinson]

Scott, Randy,

If I have to look at myself everytime I change a lens, then I won't be changing lenses very often.

Dan,

Wow, guess I have a long way to go in understanding Optics. "Plano-Convex", had to google that one.

I have looked at the lenses again and they seem to be more flat than concave on the one side versus my above drawing. I have dedone the drawing. Perhaps this may help.

So it appears that drawing one is the better way to go. I think.

[Frank Corker]

That's what I was told too - flat side down to work piece. Curved up.

[James Terry]

My college physics expert says that style of lens will focus either direction and that the focal point will simply be at a different location. As such, this might be an interesting way to get a longer focal point for those of us who have rotery jigs where the head can hit.

Perhaps some of you who have reversed the lens before might do some comparative test marking between the two to see what you get as far as focal length.

[Dan Hintz]

My college physics expert says that style of lens will focus either direction and that the focal point will simply be at a different location. As such, this might be an interesting way to get a longer focal point for those of us who have rotery jigs where the head can hit.

Yes, but the plano-convex suffers from greater spherical aberration when the spherical side is toward the substrate... in other words, you don't get as small of a focal point, which means a loss of power and bigger burn hole.

[Jordan Billingsley]

I just purchased a laser cutter from China and recently had to replace the lens. I have been digging through this forum and others but have yet to find a definitive answer to focusing lens type and orientation.

My machine uses 150W Reci Laser. According to the manufacturer the machine was equipped with 19.6mm diameter lens with a 101mm focal length. Wavelength 864 Beam Diameter .2mm
The manufacturer also gave me the common tip to look at the lens and if all of my face is visible then "it should down" and if only part of my face is visible "it should up"

However, I bought my replacement lens from Light Object. High Quality 20mm ZnSe F100mm and it is not as obvious which way the lens should be oriented. The replacement lens from Light Object definitely has more of an exaggerated curvature (the original lens seems almost flat in comparison).

So maybe.... the original lens is Plano Convex and the replacement is Positive Meniscus? Or are there other types of lenses commonly used in CO2 laser cutters?

I actually tested the replacement lens using both orientations (I hope I didnt damage the lens this way!) but it was difficult for me to tell which orientation produced a smaller diameter.

I have been reading about "ramp tests" and think that it is possible that the focusing block used with the original lens may not be ideal for the new lens.

Ok I rambled on there for a bit. But basically, is there a way to correctly identify my lens type and proper orientation for my machine?

Also, I am gathering some resources on how to "fine tune" my machine so if you have any tips or tricks I would GREATLY appreciate them!

-Jordan

[Dan Hintz]

Jordan, PM answered. For everyone else's benefit...

If the lens has a flat side (check with the sharp edge of some black cardstock or paper to prevent scratching), it's a plano-convex lens and the flat side goes towards the table. If both sides are curved (pointing in the same direction), it's a meniscus lens and the inward-facing/concave side should go towards the table.

[Dee Gallo]

Thanks Dan!