Assume you mean width?
This is most likely a focus issue, from what I can see. I’d suggest a ramp test to ensure that’s the finest line or best focus. It’s too big all around.
If you have:
- properly working tube
- clean and aligned optics
- proper focus
They work…
Ensure the optics are clean.
This can also be caused by the tubes TEM mode.
If you use a minimum power setting, you can eliminate the burnt corners. I’d guess you have both minimum and maximum the same or nearly so. Not going to fix the optical issue.
