Working with multiple laser lenses

I was wondering if anyone had come up with a good working method for dealing with camera calibration when changing laser lenses to use different focal lengths. With shorter focal lengths (1.5", 2", 2.5") this is fairly easy to do by setting up a work height that can be used with all the lenses then calibrating the focus point using the lens tube adjustment when installing the lens but with something like a 4" lens for thick materials, this is often not possible.

I suppose I could use the process to save and then manually load a calibration for the different setups but was wondering if there might be a better method or if it would be possible to have a “switch calibration” function in Lightburn where you could have a set of saved calibrations for standard setups to select from.

With the proper lens tube and nozzle, your tip to work should not vary more than a few mm. I have just under a 2mm difference between my 1.5", 2", 2.5", and 4". The lens should be mounted further up the lens tube as the focal length gets longer, you do NOT move the cutting bed down or the lens tube assy. up. Or at least you shouldn’t have to.

Thanks! It is good to hear that hopefully there should be enough adjustment range possible to use the same bed height even with the much longer focal length lens. I was hoping that might be the case but was concerned that the 4" lens might be long enough to require a different bed height for clearance since it will be substantially longer than my current lenses.

I am still waiting on the new 4" lens assembly to test out. Maybe at worst it will require one more calibration to set a new cutting bed height with enough clearance for all the lenses.

A lot will depend out your head and lens tube. That is one of the major reasons people change out their heads. Very few stock heads are designed to hold a 2.5", much less a 4", without extensions. The laser machine manufacturers try to make it sound like this is the way it’s supposed to be done. In reality it’s the way NOT to do it.

The lens should move up the lens tube away from the nozzle as the focal length gets longer. I have a head that uses the Cloudray C series lens tube. Theoretically there should be no deviation in work to tip no matter what lens I have in it. In reality my 1.5" sits a bit closer than the rest, and I imagine it’s because it sits down on the nozzle instead of behind a retaining ring in the lens tube. You will almost always have around a 1mm difference between an 18mm and a 20mm lens, but not because of the lens. For every position my hardware has a 20mm position, and a little lip 1mm behind it for the 18mm lens. For my nozzle, that lip is down for the 18mm, for two of the other three positions in the lens tube, they are up. For the fourth, or fifth if I add an extension to handle the 5" lens, they would be down like the nozzle.

Hope that makes sense.

It does. Do you use a calibration tool approach to set the tube - cutting bed height for each lens setup that is based on the exact configuration of each lens/tube configuration?

I made some step gauges and I use them first to find the ideal focus distance for a given lens and once I’ve found the happy distance I mark the gauge at that step for that lens and that’s what I use to set focus for subsequent jobs.

I have similar gauges. With the C series tubes the focal point is pretty close to the same no matter what position the lens’ are in. That said, there are differences. I just cut spacers to go between the lens tube and nozzle from different thicknesses of material to get them all about as close as I can. I also take the gap down a bit from the Cloudray factory focal point. Their lens tubes are set for a rough 10mm tip to work difference. I have some acrylic rings, taking into account the different focal adjustments I have to make, to bring them all down to a little under 8mm from the work surface.

Russ likes to get his down around 3mm from the surface for his acrylic work, but that is too close for my Premium MDF, too much resin flash on the nozzle tip. The 7.7mm gap is what I have material for to get everything the same height off the work surface and keep the resin build up to a minimum.

And then with cutting thick materials, you actually want your focal point a few mm down into the material as well.

Thanks, sounds like a good approach, especially along with the idea of shimming the nozzles and tubes to get them all to a similar work clearance to simplify switching.

Most of them are pretty close, but for what ever reason the focal point of mt 2.5" is a hair farther out than the others. So that one has a 2mm acrylic ring between the nozzle and lens tube. The rest are so close I don’t bother other than to put a + or a - on the tube to tell me to snug it down to the gauge or leave it a little loose.

For the 4" when I’m cutting thick material, especially 1x clear pine, I set it about 2mm or so closer for better cutting. It still takes 4 - 6 passes depending on moisture content. If I had a stepper controlled Z I’d set it to shift down between cuts, but multiple passes seems to work just fine for now.

Not on mine. My 2", 3" and 4" tubes have the same length between the mirror and the lens. The difference is in the length of tube post-lens.

I can’t say I’ve ever seen where you place lenses at different positions inside the tube, and I’ve cleaned/changed over 500 lenses in my time.

My tube mount allows a vertical adjustment of around 60mm which is what I use to set various tubes at the same nozzle height.

In over 20 years, I’ve never come across shimming.

The tube acts as a heat sink for the lens. You need a solid contact with the tube. A shim will not allow that.

Go have a look at the Cloudray “C” type head.

The only one I have a shim in is my 2.5", and it’s mounted in the tube so no problem. The 2mm shim is between the lip of the nozzle and the lip of the lens tube. Most of the thread is still in full contact.

That must suck to have to fight something that long.

My 1.5" mounts down on top of the nozzle and uses a retaining ring set low in the lens tube. again no problem. I too have the C series lens tube, but their E series is the same except for the tube OD. It mounts the 2", 2.5", and 4" all inside the tube. Only going beyond the 4" requires anything but tube and nozzle. Even putting the 5" in only requires a 12 or 13mm extension at the nozzle end.

I have around 75mm of vertical adjustment if I need it, but my pass through slot is very narrow so I rarely adjust it much. And with all the lens tubes and nozzles having the same tip to work gap it becomes a moot point.

BTW, it you have a 24mm or 25mm OD lower tube, the Cloudray C and E series lens tubes will slide right in.

Not really a cloudray fan, and being in NZ, not paying their exorbitant shipping - I have good suppliers for all the parts I would ever want.

Hobbyist use and the things they do is very different to professional.

I change my lens when it’s faulty, not between jobs. I use the same 3" lens, year in, year out, for engraving, cutting, etc.

I don’t have to ‘fight’ anything - what on earth are you on about?

If I read it correctly, you are adding to the bottom of your tube as you put longer focal length lens’ in if the distance between the mirror and lens stays the same.

I have 120mm of lens tube and nozzle, I have 7.7mm gap between my nozzle tip and work surface. Those numbers never change no matter what lens I have in. The lens position moves up the lens tube closer to the #3 mirror as the focal length gets longer.

No, I have multiple tubes. One for each size of lens. I can set the tube height within a 60mm range to either cope with very thick material or to get the nozzle-to-object height the same.

Thanks all,

It sounds like hopefully it will be possible to come up with a cutting bed height for camera calibration that should be workable with the different lens focal lengths without the need for individual camera calibrations. Looking forward to getting the parts on hand to see if this is the case.

You can calibrate the camera and alignment settings to each lens. Then export those settings.

As you swap lenses you and import the settings for each lens.

Ah, when you said you had the same distance from mirror to lens, to me that meant that the lower portion of the assembly got longer as the focal length got longer. Or are your tubes different lengths for different focal length configurations?