CurtPalme.com Home Theater Forum

_in_peace_ · Joined: 21 Jul 2009 Posts: 152 Location: Sweden

Hi!

I managed to push my G70 to do 1920 x 816p at 72hz and it works like a dream.

If one do this with a G90 what will be the limit? Lets say you get halfway to 4k at scoop. That would look amazing!

Can one force the netflix stream to do 72hz via Powerstrip? Any thaugths? Cheers!

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Due to bandwidth limitations we'll never get 4K on a CRT projector.

That takes 600 MHz of system video bandwidth and 1080p-60 takes just 185 MHz and that's oniy well resolved on the
more highly modified projectors.

My personal interest has been in improving the focus systems and I don't think that the tubes can even focus sharply enough
to resolve 4K with anything resembling a decent MTF value even if you were to overcome the monumental bandwidth obstacle.

4K is VIEWABLE, with the right PC video card, but that's not the same thing as being sharp and well resolved.

It's just too much of a stretch. Even I, the optimist, do not expect to see 4K on CRT.

Something better than 1080p is certainly possible. Maybe "2.5K" or possibly even "3K" but 4K? Not very likely.

I think that 2160i MIGHT be possible.

draganm · Joined: 08 Mar 2006 Posts: 8990 Location: Colorado

beautiful screen capture BTW,

4K definitely not possible,

downscale to 2K, maybe?

km987654 · Posted: Tue Jun 20, 2017 1:55 am Post subject:

A CRT Blend will help Thumbs Up

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

With the right video wall processor, I could tile four G90s together and display true 4K. Smile

_in_peace_ · Joined: 21 Jul 2009 Posts: 152 Location: Sweden

Bandwidth to go

135 / 120 x 1920 = 2160
135 / 120 x 816 = 918

2160 x 918
4096 x 1679

918 / 1679 = 55% of 4k at 2:35.1

_in_peace_ · Joined: 21 Jul 2009 Posts: 152 Location: Sweden

If you do 2.40: ratio (which is cooler) you can do a bit more.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

But wider aspect ratios demand the usage of less vertical space on the phosphor, which means the scan lines are closer together, which negatively impacts MTF and resolution. It is wasteful of precious CRT phosphor area.

It is my opinion that CRT projectors should always be run in pairs, when possible, any time the aspect ratio is 16:9 or wider. That way you can make efficient use of the phosphor space on both units. Granted, this is not something most people are willing to do,
but it is the way to get closer to optimal use of the tubes and the projectors.

I'm about to swap out a Marquee for a G90. I'm THINKING about hanging two G90s instead, in a blend setup, but there are
some obstacles in my setup that may make this impractical. However obtaining the projectors is not an issue. I only have six G90s in my workshop, in addition to a total of eight Marquee 9500LCs and 9518s.

_in_peace_ · Joined: 21 Jul 2009 Posts: 152 Location: Sweden

Very good stock you got there. There is good times now to hording CRT's.

Jeremy112 · Joined: 28 Sep 2006 Posts: 2645 Location: Fond du Lac, WI

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

The problem is that 4k is twice the horizontal resolution of 1080p AND it is twice the vertical resolution of 1080p as well.

Running a pair of projectors would handle the horizontal resolution issue but as for the vertical resolution issue, I'd have
to give you a conditional MAYBE on that.

You WOULD be using pretty much all the vertical phospor space, which is really good for getting more effective resolution
on a given CRT face.

But how much?

Well, I'd have to figure it out. You'd be able to use the full 4:3 phosphor area of the tube, or very nearly so, since two 4:3 rasters side by side would give a 2.7777 aspect ratio, which is wider than ANYTHING we'd ever need. Commit the difference to the blend zone.

Yeah, you could really get something out of this! Run both PJs in 4:3 with a small blend zone and your phosphor usage is almost 100 percent, resolution potential is maximized, light output capacity is also maximized. tube life is increased because you CAN back off the contrast and still have a great picture....there's no downside to this!

For a given screen width, if you run a 16:9 raster and compare it to a 4:3 raster at the same screen width, you increase vertical resolution capacity by 33 percent. You'd be able to run a 4x3 raster at 1920x1440 at the same scan line vertical spacing, and from here, 2160 is 50 percent more. So you may not actually want to run at 3840x2160 but I think that 3840x1446 or 3840x1600, spanned across two projectors, would look rather awesome.

As for bandwidth requirements, let's assume a 10 percent blend zone and figure each projector's bandwidth needs.

1920+10% multiplied by 1600 multiplied by 60 Hz and then add 20 percent for sync and other non-displayed signal information,
and you need, call it 243 MHz bandwidth. That's a bit more than we can probably manage. But it's onily 219 MHz bandwidth if you drop to a vertical resolution of 1440.

It's plausible. You'd probably be out of the FLAT bandwidth range, but I think it'd be visually pretty acceptable.

If I had the blend solution in hand I'd be drawing up my placement plans for two G90s right now.

**AnalogRocks** · Posted: Tue Jun 20, 2017 10:30 pm Post subject:

When you look at a tube face it's more like 5:4 ratio no?

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

I haven't actually measured that but that actually helps if true.

Set both PJs to QXGA (2048x1536) and blend the middle area. Not a problem, and it uses an industry standard resolution that should be readily accessible.

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

FYI, on a Marquee, the frame window dimensions that the CRT mounts in is 4 and 3/4 by 6 and 1/4 inches. This is the absolute maximum possible usable raster size on a Marquee at least.

jbltecnicspro · Joined: 23 Apr 2016 Posts: 512

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

Some people are more, and some less, sensitive to flicker. If you are less sensitive, you might be able to run a slightly lower refresh rate. I know that I don't see flicker at 60 Hz and apparently, flicker on direct view PAL sets running 50 Hz (OK, 25 and interlaced) wasn't a problem or they'd have gone with a higher frame rate.

By reducing the frame rate, perhaps to as low as 50 Hz, you recover bandwidth. Let's just guess that you may be fortunate enouigh that you can even tolerate 48 Hz, which is a magic number as it's even 2:1 pulldown for 24 FPS film sourced materials.

That saves 20 percent of your bandwidth requirement, which cancels out the bandwidth overhead needed for sync and timing and non-visual information. So all you have to do then, to calculate bandwidth requirements, is a simple and straight calculation of H pixels x V pixels x frame rate. So, 2048x1536x48 brings our bandwidth commitment down to 151 MHz, and that is well within range of any decent 9" CRT projector. 1080p-60 needs more.

It's still not 4K but it's a pretty respectable chunk of it.

A G90 is capable of syncing up to a 24FPS input signal. Flicker city, of course, but with that information in hand, at least a G90
could actually display a 4K-24 signal as it would be around 200 MHz video bandwidth required, IF you could tolerate the flicker
and IF you had a way to actually get it to the screen. (I think that the Moome HDMI 1.4 card is technically capable, at 24 FPS.)

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

So I checked on what happens below 60 Hz refresh rates.

The Marquee synced up fine at 48 Hz. I did not attempt anything less. as it was flickering enough to annoy even me,
and I'm pretty tolerante of flicker.

50 Hz was better, the flicker was there but not bothersome.

However, picture width shrank CONSIDERABLY. I'm trying to figure out why that happens. I didn't expect it.

The amount of width lost could not be compensated for with the H. size control, not at 50 Hz. Picture width started
to come back as the refresh rate was raised above about 55 Hz.

What I'm thinking is happening is that the low refresh rate is taking the horizontal deflection coil out of resonance with the HDM circuit. In which case, it MIGHT come back as the resolution (and scan rates horizontally and vertically) is increased.

_in_peace_ · Joined: 21 Jul 2009 Posts: 152 Location: Sweden

Yes i think 60hz is quite nice. It gives a pulsating feeling almost like on old cinemas. I do not have a G90 my self but it sure will perform some extra resolution.

ronaldus · Joined: 25 Dec 2010 Posts: 183 Location: france

cmjohnson · Joined: 03 Apr 2006 Posts: 5180 Location: Buried under G90s

I suspected that a different HDM may yield different results. Hadn't tried it yet, though.

I do believe that the loss of width is in fact due to the overall h. scan rate dropping out of the resonant range
of the tuned HDM-yoke circuit. But increasing the number of lines scanned (higher vertical resolution) should
bring it back up into resonance.