So tell me about GaAs lenses

[Kev Williams]

Need to replace my dirty, burnt, scratched and cracked 2" lenses I've been using in the Triumph. For fun I bought a couple of GaAs lenses.

Pretty cool to look at, no visible light penetrates. I know a red laser pointer won't penetrate either, but I'm not worried about that so much. I'm just curious how they'll work, if I'll see any difference, bad or good?

Funny thing is, as bad as my old lenses are, they all seem to work okay when engraving. But I'm thinking I might be losing some cutting power, or maybe more accurately, cutting DEPTH.

Anyway, before I try out a lens that looks like a mirror, thought I'd be sure it's NOT

[Dave Sheldrake]

Gallium Arsenide lenses are a lot more resistant to scratches, usually they are Plano - Convex though ,the biggest problem is quality...good one's are fantastic,bad ones can be dire,the problem is due to the reflective coating you can't see if there are any inclusions in them or any flaws in the manufacturing process. You can usually tell when they are bad ones, they Halo very quickly (you end up with dark concentric rings on the coating through uneven heating)

Make sure you use them flat side towards the material though Kev, the other way they tend to scatter

meniscus is the best for beam profile to be honest,

Most of the better DC tube makers now use GA optics in the end of the tubes as they are less likely to get damaged by over enthusiastic users cleaning them with an angle grinder

[Kev Williams]

These are from China so I'm not under any delusion that they're 'high quality'

Another interesting aspect with them is that the flat side isn't flat, it's concaved.

The cheap lenses I've been using are okay for engraving quality, but I do a lot of leather engraving, and the smoke tends to collect very quickly to the lens(es). So what happens is, if I don't clean them soon enough, the soot burns to the lens, which ends up with a dark spot, or a cracked lens. And if I DO keep the lenses clean, just cleaning them scratches them up quickly...

So as long as I get the same basic engraving quality out of these AND maybe a little more resistance to my frequent cleaning, then the $18 each I paid for them will be worth it!

[Neville Stewart]

These are from China so I'm not under any delusion that they're 'high quality'

Another interesting aspect with them is that the flat side isn't flat, it's concaved.

The cheap lenses I've been using are okay for engraving quality, but I do a lot of leather engraving, and the smoke tends to collect very quickly to the lens(es). So what happens is, if I don't clean them soon enough, the soot burns to the lens, which ends up with a dark spot, or a cracked lens. And if I DO keep the lenses clean, just cleaning them scratches them up quickly...

So as long as I get the same basic engraving quality out of these AND maybe a little more resistance to my frequent cleaning, then the $18 each I paid for them will be worth it!

Kev - check your SMC mailbox - I asked you about rotary engravers.