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Has anyone ever heard of a circuit to automatically adjust the focusing anode on an electrostatically deflected CRT? Is there any way to even detect optimum focus other than by looking at the tube readout? I know on old CROs theres just a focus knob, but a lot has changed since then and I figured maybe something more modern would enable automatic focusing based on small current draw changes through electrodes or something like that. (?)

CrafterOfWorlds
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  • building a scope and wondered if anyone had heard of such a system – CrafterOfWorlds Aug 16 '19 at 05:17
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    In 40 years I have never heard of such a setup. Stable focus settings use very stable voltage references. There is no built in feedback loop for this except for the users judgement about the focus. –  Aug 16 '19 at 05:23
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    There are no measurements that you can do on a standard CRT which will indicate anything about the focus. The idea you had with measuring small current changes is not going to work because there is no change in current caused by adjusting the focus. The CRT just launches electrons from the electron gun in the back and then they come flying towards the phosphor on the front where they create an image, what happens to the trajectory of the electrons along the way does not affect the current flow, voltage or any other parameter that you can measure, sorry. –  Aug 16 '19 at 05:56
  • Might be a way using something like a thin film solar overlay and have an auto focus procedure based on light bleed over targeted regions... but that's getting insanely complex for something that a user should only need to do every once in a while with a knob. The only methods I can think of would require a way to directly measure the accuracy of the beam once it's reached the phosphors. – Jarrod Christman Aug 16 '19 at 15:09

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