[rayscott]

I would guess that your 100mm lens does not have such a small spot size. It is typical that as the focal length gets longer, the spot size also gets larger. If the beam spot size is larger, then you need to cut away more material to get the same depth as the 50mm lens went. I recommend many of my customers purchase a 63.5mm lens to try cutting slightly deeper than the 50.8mm lens typically goes. As the target material gets less dense (like foam, sponge, and Styrofoam).. then you can use longer FL lenses and fatter spot sizes.


..and then adding air will help too.

[HomerSimpson]

Thanks for your reply. I tried my experiment with the 50mm and 100mm I quoted originally, as well as with a 190mm lense. None showed an effect. If you think a 63.5mm lense will have an impact, it suggests a massive non-linearity in the effect, given that the lenses that bound it, 50 and 100, show no effect.