I think you get the idea. While the center of the screen is the throw distance, what you have to be careful of is that the corners can be up to 11" closer than the center to the PJ. This in turn could lead to you being a bit to close if you are using max raster.
I think Vince's problems had to do with pin and bow if its the fellow I'm thinking about who set up a G70 on a Torus in Savannah GA. The XG's have a bit better range of control for the bow and pin than the G70's.
I have been giving this some thought for awhile now. The curves will be somewhat determined by the gain. The higher the gain the deeper the curves. Since most are using the Pearl, you could probably follow the curves that they are using. In Vince's Torus lite thread, he seemed to be fine with the vertical curve of 1.75". The horizontal curve seemed to be a little shallow and hotspoted at 3.5".
So the tradeoff is hotspotting if the curve is too shallow, and loss of focus in the corners if the curve is too deep, yes? Vince's original curves were too deep, but he also had a significantly smaller screen than what I'm shooting for.
Sometimes I feel like I'm overloaded with information on the Torus screens. It seems like a variety of curves work for people. Hifi, since you're happy with what you got and are also using an XG, that's a strong recommendation.
The main problem I had was running out of bow control. One really good thing that I realized out of my experience is that you should check out the pjackso spreadsheet for two reasons - he gives gentle curves that will minimize your geomtry issues, focus issues, etc; and the great, great thing is he plots where to measure to setup your curve without getting out in the driveway with wire and pencils etc. (not that I know what that's like )
I was planning to use curves from -Pjackso's spreadsheet, which (for an 85" wide screen, 10' to viewing distance, 4' wide viewing area) has 3 5/16" H curve and 1 1/16" V curve. Vince didn't say his screen hotspotted (right Vince?), but it did drop off a little bit at the edges. Maybe the deeper curve would completely avoid all hot/warmspotting, but then you run into focus issues. The shallower curves seem like a good compromise.
Oh I definitely have hotspotting, have you checked out my pics in the Torus Lite thread? It's not the hotspotting that remains that you should focus on, it's the compromise between a deep dish with no hotspotting and difficult geometric/focus issues and the heinous hotspotting/colorshift of the pearlbrite when it's flat - put it this way, even with the flat pearlbrite I would have to think hard if I could give up the gain, the torus fixes that issue. I meant to someday post some comparisons of the flat pearlbrite but haven't gotten around to it. The pics I linked to exxagerate the hotspotting and color shift versus what you'd see in the room, but critical viewing will pick up on it anyway.
[philosophy] Like alot of things, it's a compromise but a worthwhile one. I think many products that you use have compromises built in that you're not aware of, when diy'ing there is a tendency to get hung up on perfection - I enjoy the process of compromise and the limitations of the technology. You can't have perfect convergence, geometry and brightness consistency when using a curved screen unless you have special lenses for the curve. Even then when off axis you'll have geometry issues. Of course the fun of a curved screen also weighs into it, it's just cool. Hey, when my wife notices the pop from it, it's not subtle (she's getting better, now she can tell HD from DVD, I'm so proud). [/philosophy]
brightness pop - you won't go back to unity gain
3-d effect - from increased CR, again a stunning difference
ambient light rejection - don't care that much but it's an improvement
really cool movie theater feel - it's a unique feature for your room
focus - the big one - stick to pjackso curves or milder to minimize this
geometry - really not a big deal, what crt is perfect? I decided the curved screen
actually makes the geometric deficiencies of the pj less noticeable
hotspot/colorshift - again keep the curves mild
weird echo from screen - doesn't seem to be an audio problem, only amplifies
sounds back to the source
torus is not rocket science - don't make it so.
keep it simple as possible - see my fan box design in the torus lite thread.
don't get hung up on optimizing the curves, angles, etc for your room. First build
a torus and then decide if you care about that last 15% improvement - it's not
dont' get hung up on fancy fan needs such as pressure switches, just put a
variable resistor in line and turn the fans down as needed - it's not rocket
So the torus isn't perfect -- especially if I can't get my 10-yr-old to shut up during movies -- but it's a big increase in pop and depth, and that's what I want. I'll be using Paul's curves so hopefully focus and geometry won't be a big problem. Gotta either dig up a few small fans from the junkpile or go find a nice quiet 120mm fan. But with an XG in a not-great hushbox, I doubt I'd hear a fan behind the screen anyway.
With the number of cons listed above I was wondering if using a 1.5 gain screen in a torus lite frame would still have some of the benifits like added depth and a little more brightness but without as much hotspotting(due to swallower curves and the 1.5 gain) and less colour shifting. Lesser curves obviously is less strain on the geometry circuits and the convergence.
I'm no expert, but I would think 1.5 would be too low a gain. Low gain means the light is being dispersed in all directions, which (on a curved screen surface) means that one part of the screen can wash out other nearby areas.
Iceman's study used 2.0 and 2.8 material for the torus. I don't know if he modelled washout or not.
If you were going to use 1.5, I'd use really shallow curves.
Yeah the depth of curve is totally related to the gain of your material, so you could probably get away with a pretty damn shallow curve with say a 1.8 material if you were only looking for a mild gain increase.
What I'm more interested in at the moment is how a *really* high gain material will cope, and wether colour shift will be a serious problem no matter what the curve.
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