Camera calibration: perfect in the center, off in the corners (X and Y) - Lens or Alignment issue?

[BrianF84 (Brian)]

Hi great LigthBurn folks,

I’m struggling with the camera feature for quite some time now and I have read all that I can find about that matter but I can’t figure out what might be the cause of my issues.

I have a 8 MP Network Camera attached to the lid of my self made machine with a 1000x740 mm bed. I can very easily calibrate everything to get quite good results in the center but, whatever I do, I’m always getting off by 1-5 mm at the corners and to improve things I really would like to get some suggestions what might be the cause of this. I’m also aware that it might even not be possible with larger bed sizes to get this to work in the corners as well so I would love to hear from others if it is basically possible or not.

So what will influence the accuracy in the corners? The lens calibration being not perfect or the alignment? I’m also aware that the camera should be always in exact the same position and that it can cause isses if it is mounted onto the lid but I have the understanding that issues with the camera mounted onto the lid should only cause position offsets on the y axis?

My camera has an inbuilt way to get rid of the fish-eye which get myself quite good results for the camera itself so I have tried to use the inbuilt lens adjustment and did the LightBurn lens calibration on top of that (in normal lens mode). But I also tried all other possibilities. I just would like to know which mode should be the best to start with so that I can concentrate on that (without the inbuilt lens adjustment and in fish-eye mode, with the inbuilt adjustment and with normal mode, with fish-eye mode as well and so on).

I cut the alignment with a scale of 360 which will use almost the maximum size of my bed. Is it possible to get the alignment setup as a single file to tinker with the marking on the material?

And to test the final alignment I write some “x” on the corners and the center of my material also used for the alignment and jog the laser to the exact center of my written “x” using LightBurn and compare my beam-aligned red dot with the position of the “x” I have written on it. It is quite perfect in the center and it shifts in the corners, but not in the same amount in x/y to just manually adjust the size in the camera tab.

Here is an illustration of the position difference, the “x” is written onto the material, captured and the laser head has been jogged with LightBurn to the exact center of the “x” but was actually where the red dot is written on the illustration:

So long story short: what are your suggestions where to change/recalibrate my setup? Lens? Alignment? Both? Something different? Or “just live with it as it is”?

Cheers,
Brian

[LightBurn (Oz)]

Can you show what your camera sees through the preview in LightBurn?

Does your machine use a variable height Z table, or do you move the laser head up & down to adjust your focus? The camera system requires that the material surface always be at the same height / distance from the camera, so if you are changing that, it will affect the alignment.

[BrianF84 (Brian)]

Thank you for your reply Oz!

My machine has a variable height Z table but I haven’t touched the lid or the table/Z height during the whole process of calibrating and testing the alignment. But has the table to be perfectly leveled? My machine is perfectly leveled but I have an issue with a bad honeycomb table that is not completely flat. I’m in the process of making a self-made knife table that is quite flat - I will redo the test with that table.

If I redo those tests, can I concentrate to the alignment process or should I redo the lens calibration itself? I know those two are independent, just want to know if a (bad) lens calibration do could have the same effect?

Here a screenshot of what my camera is seeing (with the inbuilt lens adjustment enabled) and how the lens is calibrated to my table:

Cheers,
Brian