Lens choices for a 20w fiber laser

[Mechhead]

My machine came with a 150mmx150mm area lens. Options are 50mm, 70mm, and 100mm. I want to mainly do deep engraving on brass and steel. I understand that the wider the field, the less power density you will have at the spot. I have found a chart showing the spot sizes and power densities, but it doesn't mean much to me in real world terms. Can someone explain if going to a 50mmx50mm area lens will really allow me to engrave deeper faster with less repetitions?

Similar Threads:

• Fiber Laser Engraver, Fiber Marking Machine
• AK10F- A Portable Fiber Laser Marking Machine for Plastic, Fiber and Metal Engineerin

[Storen]

My machine came with a 150mmx150mm area lens. Options are 50mm, 70mm, and 100mm. I want to mainly do deep engraving on brass and steel. I understand that the wider the field, the less power density you will have at the spot. I have found a chart showing the spot sizes and power densities, but it doesn't mean much to me in real world terms. Can someone explain if going to a 50mmx50mm area lens will really allow me to engrave deeper faster with less repetitions?

The spot size of 50 and 70 is usually very similar (depending on the quality of the optics). I would suggest going with 70 and yes, It would engrave deeper than 150.

[Mechhead]

The spot size of 50 and 70 is usually very similar (depending on the quality of the optics). I would suggest going with 70 and yes, It would engrave deeper than 150.

The focus spot size for my current lens is 34um. The 50mm is 12um and the 70mm is 16um. Does this mean that given the same power and speed settings, the 50mm lens would engrave almost 3x deeper per pass? I can get lenses from the same manufacturer (Cloudray) for $108 each. To me that's not a lot, so would it be worth getting both? Or would you still say that just the 70mm would be the best choice?

[Storen]

The focus spot size for my current lens is 34um. The 50mm is 12um and the 70mm is 16um. Does this mean that given the same power and speed settings, the 50mm lens would engrave almost 3x deeper per pass? I can get lenses from the same manufacturer (Cloudray) for $108 each. To me that's not a lot, so would it be worth getting both? Or would you still say that just the 70mm would be the best choice?

The spot size will vary quite a bit across the scan field. Even more with cheap lenses - expect very low-quality control. It is like playing a roulette. If you are lucky you may get a 70mm lens with smaller and more uniform spot size than 50mm.
My advice is instead of buying 2 dirty cheap Chinese lenses to get one with more average quality.
I think Cloudray is an online store, not a manufacturer. It looks like they sell the cheapest and lowest quality parts available in China. It is always better to buy from the manufacturer directly. You can save some $ of the reseller's markup and it would also guarantee you will get new, not a refurbished part.

I would suggest getting a wavelength-tech SL-1064-70-100 lens ($350 I think). Their production standards are significantly higher than those of the low-cost manufacturers.
They also have a Fused Silica line which is even better.