AVS Forum banner

Status
Not open for further replies.
1 - 20 of 20 Posts

·
Registered
Joined
·
24,883 Posts
Discussion Starter · #1 ·
I'm considering, in the near future, going to 9" CRTs. There are some on the forum who use 2.4:1 or so aspect ratio screens with their CRTs. I know that this is an inefficient use of phosphor from the perspective of both light output and resolution. I was wondering what thoughts you folks have on screens that are any wider than 1.78:1 and PQ with your CRTs?

Art
 

·
Registered
Joined
·
667 Posts
Art,


I too intend to go with a 2.35:1 or 2.40:1 AR screen for my next HT (along with a larger room in a larger house with a larger CRT).


The way I look at it:


* Most every cinema uses "constant height".

* The height of the image is what gives the "big screen" feel

* Black bars to the left & right are less noticeable, especially at first

* Especially with a 9" the light output consideration is very minor (the extra light from the small decrease in throw distance will be very small)

* Resolution is unaffected by phosphor use AFAIK


Of course the "constant area" idea floating around this forum is probably the ultimate answer, provided you have the inclination to create a complex masking system.


Paul
 

·
Registered
Joined
·
5,313 Posts
Runco DTV-991, flat white screen, it's plenty bright enough to light up the room on a bright scene. I have optimized the use of the available phospher by making the width of the raster extend to within 1/8th of an inch of the tube face edge. The 2.40 image extends to within 1/4" of the tube face edge.


Vern Dias
 

·
Registered
Joined
·
3,053 Posts
Art stated:

> There are some on the forum who use 2.4:1 or so aspect ratio screens with their CRTs. I was wondering what thoughts you folks have on screens that are any wider than 1.78:1 and PQ with your CRTs?
 

·
Registered
Joined
·
4,916 Posts
Art,

I'm with Tim on this.

If the goal is to go with a larger screen and display 2.35 material, the wider the screen, the further the CRT has to go back and some of the "punch" will be lost on the PQ.

Besides, if you ever have any intentions of displaying HD you will be sacraficing that picture quality as well in that you would not be using the full width of your phospher.

Short of a 4:3 screen with 4:3 material maximizing full raster, it's all a compromise w. FP CRT's. 2.35 is just a worst compromise.


Terry
 

·
Registered
Joined
·
3,053 Posts
I was hoping that perhaps Gertjan would jump in here, since he was grappling with the same issues a while back and decided to just try 2.40 for the heck of it. He liked it well enough to stick with it as his standard setup. I'd be interested to hear his comments.


One possibility that could be used to achieve optimal results in multiple ARs on a fixed height screen, although admittedly not overly practical, would be to mount the PJ on tracks, and slide it into the proper position for each AR. On a fixed height, 48" tall screen, this would require sliding the PJ ~32" forward, when moving from an AR of 2.35 to 1.78. The 2.35 would fill a 9'4 wide screen, and the 1.78 would be 7'1 wide.


This would also involve dropping the PJ a little less than 6" in the process. So if the sliding track was ramped downward (with the PJ counter-angled to maintain a horizontal), you could converge two memories, one at each location. A lot of work, but if you're really looking to replicate the theatre characteristics, with no sacrifice in PQ at any AR...


OTOH, if you're using dual PJs to get maximal light output, this becomes even more impractical.


- Tim
 

·
Registered
Joined
·
24,883 Posts
Discussion Starter · #7 ·
Thanks for the comments. Remember one man's hare brained scheme could be another man's stroke of genius! In this case however I think that one will remain as a paper study at most for me:D

I was less concerned about light since my intention is to stack two 9" CRTs also but the loss of resolution ( the main reason I have for going up to 9") would be lost , I'm afraid, with the constant height screen. The comment about HD being largely 1.78:1 also seems very important. If it seems like I'm looking for someone to help me fall one way or the other I am. Thanks.

Art
 

·
Registered
Joined
·
1,745 Posts
Art,

This thread was about using 2 heads off the video card so that 2 projectors display the image by splitting it digitally left and right.
http://www.avsforum.com/avs-vb/showt...hreadid=140591

Unfortunately, I find this thread doesn't come up for me today...I hope it is just a temporary forum problem.


As I recall, 2 projectors can utilize virtually all of their phosphor and still display a high aspect ratio. I also recall that convergence is much easier (than typical stacking) but that the projectors would have to be very close in color temperature so that the picture looks the same from left to right. Brightness is the same as typical stacking.
 

·
Registered
Joined
·
5,313 Posts
VideoGrabber:

Quote:
First off, most HT screens are width-constrained. I.e., in most of our theatres, we run out of room for the screen horizontally, before we do vertically.
We do??? I don't have single room in my house (except two small bathrooms and a hall) where the height of the room is greater than the shortest horizontal dimension. My media room is 18' wide x23' long x 10' tall.

Quote:
when viewing other AR source material (many DVDs at 1.85 and HDTV at 1.78), the PQ is naturally reduced over what it could be if greater height was utilized
Not in practice, at least in the CRT world, because the resolution of the CRT and the phosphers are so much higher than the resolution of the source, even HD. On a fixed pixel projector, such as LCD, this argument would apply.

Quote:
Also, if these sources comprise a significant portion of your viewing material, you run the risk of extra wear within the center of that narrow 2.35 strip.
This is true, however no more true than the converse of running 2.40:1 in a constant width setup.


I say this respectfully, however I really think that only people who have actual experience in running a 2.40:1 setup have the true real-world experience to answer these questions. All else is speculation. And I don't know of a single person that has tried this setup that has gone back to a constant width setup. I believe that says something.


Chuchuf:

Quote:
If the goal is to go with a larger screen and display 2.35 material, the wider the screen, the further the CRT has to go back and some of the "punch" will be lost on the PQ.
Punch has nothing to do with the throw distance between the projector and the screen. It has everything to do with the ratio of phospher area to screen area. The light loss through reasonably clean air is neglible. I remember working as a projectionist in a drive in theater where the throw exceeded 200 feet.



Anyhow, as always, YMMV.


Vern
 

·
Registered
Joined
·
251 Posts
Tim, you forgot about focus issues in your grand plan, a killer with CRTs.


I think the approach to use with this is the 2-head approach, either with PC-style video cards or with dedicated video-wall electronics which performs edge blending. The phosphor utilisation is much better, too: two 4:3 PJs side by side gives 8:3 or 2.66:1 without any edge blending, or with a 10% edge blend you get 2.394:1. Imagine! Full phosphor utilisation and a lovely 'scope presentation.


Not easy to do if you don't want to spend $$, though.


- David Eddy
 

·
Registered
Joined
·
24,883 Posts
Discussion Starter · #11 ·
Vern,

I'm not questioning you veracity on this but since I probably won't have a chance to visit you( assuming that I would ever be invited) my opportunities for first hand comparisons are shockingly limited! The only other person I know who had done this was Gertjan ,who seems to have fallen of the earth lately. Without some more first hand stuff sometimes the negatives brought up are as useful as the positives. I just simply would love to not have scope films look smaller than academy flat.


P.S. the dimmest projected film I have ever seen is at my local drive-in (the Capri in Coldwater MI )


P.S. again... My physics professor said that light energy falls as the inverse square of the distance.

Art
 

·
Registered
Joined
·
5,313 Posts
Quote:
P.S. again... My physics professor said that light energy falls as the inverse square of the distance
Isn't that because it is spreading out as it goes? I don't think that holds true if you put it through a lens.


At least I know that a theater with a 50' throw and a theater with a 100' throw will put the same amount of light on the screen (assuming the same size screen, and the same wattage Xenon)

Quote:
the dimmest projected film I have ever seen is at my local drive-in (the Capri in Coldwater MI )
Yeah, it's probably a 100' wide screen with old weatherbeaten flat white paint on it, too.


BTW, you are invited if you ever get this way. :p


Vern Dias
 

·
Registered
Joined
·
667 Posts
Quote:
Originally posted by Art Sonneborn
but the loss of resolution ( the main reason I have for going up to 9") would be lost , I'm afraid, with the constant height screen.
Are you sure you lose resolution? With CRT we can squeeze the full resolution into narrower or shorter areas.


Seriously consider a "constant area" approach:


I couldn't find bjorn's original post (do some searching) but found this one which gives a good description of what he has done:

http://www.avsforum.com/avs-vb/showt...=constant+area



Also consider how much of your collection is 2.35:1 vs 1.85:1. This might help you make your decision (my collection, unfortunately is about 48% / 50%).


Paul
 

·
Registered
Joined
·
3,053 Posts
Vern,


good points, and I won't quibble with most of them. However, regarding width-vs-height constraints...


> I don't have single room in my house (except two small bathrooms and a hall) where the height of the room is greater than the shortest horizontal dimension. My media room is 18' wide x23' long x 10' tall.
 

·
Registered
Joined
·
3,053 Posts
Art wrote:

> my intention is to stack two 9" CRTs also but the loss of resolution ( the main reason I have for going up to 9") would be lost , I'm afraid, with the constant height screen.
 

·
Registered
Joined
·
251 Posts
There's a thread happening in HTPC at the moment which is talking about the new Matrox "Parahelia" gpu (and card), which is a triple-head and features support for hardware overlay which spans 2 heads. $400 according to PC sites out there, although it apparently hasn't yet been released.


This sounds all jim-dandy except that the question of whether there's any edge blending going on between the heads - if not then I wonder how difficult it would be to maintain a seamless join between two PJs. On the poisitive side, the Parahelia is supposed to be intended for 'surround gaming', so perhaps this feature will be built in.


- David Eddy
 

·
Registered
Joined
·
5,313 Posts
Quote:
Unless you're planning on doing square screens, you'd still wind up width constrained, in most cases
Only if you are planning a floor to ceiling screen.


In the real world the bottom of the screen has to be at least 4' from the floor to allow for sight lines, etc. Any you don't normally want the top of screen 10' off the ground or you'll wind up with a stiff neck every time you watch a movie.


I guess I didn't make myself clear.


In my environment, I do find myself width constrained, I guess, but only because my choice of speakers takes up 3' of the short wall in the media room.


Vern
 

·
Registered
Joined
·
24,883 Posts
Discussion Starter · #18 ·
I think that the resolution,and light output would be the highest with two fully used 4x3 rasters blended at the center resulting in a 2.4:1 aspect ratio, but getting two PJs to show no seam including geometry,color balance and focus with the interface right in the middle of the screen:eek: !!. The issue of academy flat being too small would have theoretically been addressed through a 12' wide screen for scope and 9' wide for academy flat ( academy flat is 9' wide on my present screen).

Paul,

My understanding is that using less raster puts the same beam spot size in less space therefore line overlap at the highest resolutions e.g. 1080p.

Tim,

But since the throw for CRTs is essentially fixed then the 1/Dsquared formula would apply since the screen size would increase as the projector to screen distance increases.Yes?

Art
 

·
Registered
Joined
·
667 Posts
Quote:
Originally posted by Art Sonneborn
Paul,

My understanding is that using less raster puts the same beam spot size in less space therefore line overlap at the highest resolutions e.g. 1080p.
Hmm. That does make sense however I wonder where one would find 1080p source material. Would the end result not be the same if the PJ is run at the highest resolution that does not overlap (provided that particular resolution is higher than the source)?


I'll need to ponder this one. I have yet to set up my HTPC so I don't have much 1st hand exp on this one.


Great thread BTW.


Paul
 
1 - 20 of 20 Posts
Status
Not open for further replies.
Top