I've ordered a light optics laser head with air assist but forgot to order

Lasers
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1

I’ve ordered a light optics laser head with air assist but forgot to order a lens. I’m in the UK so going to order one locally but what focal length should I look for to work with the standard K40 bed? There seem to be 3 options from 1.5" to 2.5". Also is an HQ Znse lens good enough? Looking at a few other threads this seems good enough for the K40 but I’m not certain. Thanks!

2

Shorter focal length for engraving, longer for cutting. I use a 50.8mm, most of what I do is simple engraving on and cutting of .125" hobby plywood and acrylic.

3

I use the lightobject HQ ZnSe lens and head btw. Cut some small washers for both sides of the lens - the holder WILL scratch a circle into it where lens meets opening.

4

Thanks, I usually cut so,maybe a 2.5" lens would be better?