On 16 Feb 2016 14:58:34 -0800, you wrote:
I suspect almost all of the intensity dependent spreading around theThe reason I think it is secondary emission and not an optical effectI see both the outer, constant and abruptly delimited shape, which speaks for the secondary emission, *and* intensity-dependent amplitude and spread of bleeding around the trace, which I see as the scattering/dispersion in the phosphor and aluminium coating. Interesting to discuss this, David! Unfortunately, I think I'll have to stop soon since my observations aren't very sharp at this late hour...
spot is caused by an increase in emission area from the cathode which
prevents proper focus. This is also why aged CRTs with low cathode
emission have a thick trace even at normal intensities where it should
still be sharp.
If it was an optical effect, then removing the PDA to produce a dimmer
spot would also decrease the spreading but that is not the case where
I have tested it. Under that condition, the spot spreads
significantly even though the brightness is low from a lack of PDA. Of
course this also increases the spot size simply because the electrons
have more time to spread out.