VOGONS


Moire or something else?

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First post, by sketchus

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Just want to see what people think. I picked up this monitor yesterday, a Sony Multiscan 15sf. It's a lovely little Trinitron PC monitor. One thing I noticed though is that on solid colours, theres a pretty clear curved colour distortion effect. It doesn't effect geometry, just colour, and depending on the resolution it changes location, with some resolutions (the lower ones) not showing it at all.

I'm thinking this might just be normal, possibly moire, but would like to get some thoughts.

For reference, I had to edit the image slightly to make it easier to pick up on camera, and the distortion in the lower right/middle is from the camera, not the CRT. What I'm talking about is just to the left of the mouse, and runs top to bottom, with a curve, and that's visible to the naked eye.

https://ibb.co/W4LtmmF5

This second image shows it more clearly. Left third of the screen.

https://ibb.co/Pz10kfDG

Something I noticed is that if I use the controls to rotate the image, the line rotates with it, which makes me think it is more likely moire. If I move the image left to right, it stays in place.

Reply 1 of 7, by wierd_w

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I cant seem to see your images, but there should not really be *moire* patterns on a trinitron, because it is not a shadowmask tube.

It's an aperture grille tube instead.

https://en.m.wikipedia.org/wiki/Aperture_grille

Aperture grill tubes have perfectly stacked columns of phosphor triplets, instead of trigonally staggered circular triplets, like a shadowmask has.

https://en.m.wikipedia.org/wiki/Shadow_mask

It's this trigonal arrangement that produces moire patterns on some crts when displaying certain images, or when seen through certain filters.

The more modern counterpart to how the image is generated would be an IPS display, which is ALSO perfectly stacked columns.

https://www.dreamstime.com/led-ips-monitor-sc … -image139507428

Reply 2 of 7, by sketchus

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Thanks, I actually did stumble across the information that moire is not an effect of the Trinitron tube, I wasn't aware it only affected shadowmasks.

https://imgur.com/a/KeXnOSB

That's an Imgur album of the photos if that works for you.

Reply 3 of 7, by wierd_w

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That looks more like a VGA 'jailbars' artifact.

It's a phase alignment issue on the per-scanline timing.

Reply 4 of 7, by sketchus

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Anything I'm likely going to be able to fix?

I wonder if the issue is Windows 98 is detecting it as a plug and play monitor, but I can't control the refresh rate, I only get the choice of Optimal.

EDIT:

I was able to force a driver install, and I can choose refresh rate. Changing it just changes where that bar is on the screen.

Reply 5 of 7, by wierd_w

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Try adjusting the 'pincushion' knob on the monitor. 😉

As for 'jailbars' in general, these are caused by very subtle variations in the analog signal generated by the video card's RAMDAC. They were a common complaint back in the day.

Your images show pincushion distortion, which is caused by improperly adjusted magnetic deflection plates inside the monitor.

The pincushion issue is fixable with the appropriate knob/osd setting.

The actual jailbar issue, is just caused by your card.

Reply 6 of 7, by sketchus

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I'll have a play with the pincushion in a bit, thanks that's really handy to know.

With these jailbars is it typical to have one curved one? It looks very odd, but has more or less the same characteristics just moved based on resolution or refresh rate. I have a second Proview CRT, and when I plug that in, I have no issues on exactly the same PC and desktop.

My w98 build has a Voodoo card in it too, I wonder if it's worth testing that too.

Reply 7 of 7, by wierd_w

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That curve is the afore mentioned pincushion distortion.