Making a new screen - curved or flat? - AVS Forum
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post #1 of 6 Old 08-06-2013, 04:29 PM - Thread Starter
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Hi everyone,

I have a new projector and plan to make a new screen for it. It will be a 'zero edge' type sitting a few inches from the back wall (I want to experiment with backlighting) and be a 120" scope screen. I will mount the projector near the max throw for best contrast - brightness is not a problem as I am running on low lamp power with the iris at a pretty low setting. The room has total light control but has light walls. Depending on how the screen turns out I may look at darkening surfaces but I have the benefit of distance with around 6' each side of the screen and a high stud giving 5+' ceiling to screen top.

My question is what is the current thinking on using a curved or flat screen? I will be zooming, i.e. no anamorphic lens. If there are benefits with a curved screen, are they negated by pincushion/focus issues?

Many thanks for your help.
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post #2 of 6 Old 08-06-2013, 05:08 PM
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The ONLY reason to consider a Curved (Torus) Screen is to mollify, mitigate, or otherwise eliminate "Pin Cushion Effect" .

You do not mention the PJ your using, but most in your position use a Flat screen, and what is called "Constant Image Height" (CIH) There is no Pin Cushion Effect on a Flat surface...that nice little issue is the sole property of the Anamorphic Lens itself as it tries to stretch 16:9 out to 2.35:1. But without such a A-Lens, of course such cannot even happen, so then your back to CHI.. (...although some PJs do posses a 2.35:1 Mode to accommodate a A-lens and it's peculiarities...)

A very Few Projectors with Lens Memory (Panny 7000/8000) and really effective Top/Bottom masking make CHI a veritable snap.

All other such efforts do depend upon having a PJ with BOTH Lens Shift and Zoom

I'm pretty sure your aware of all this, so no more "Preachin' to da Choir".

As far as a Screen suggestion, I must wait for indicative information as to the type of PJ you have and then, using 120" diagonal (...that's a wussy sized 2.35:1 cool.gif ) as the benchmark,along with the maximum throw (...a bad idea....contrast can be improved "on screen / with screen surface more effectively...) to achieve such, it will then be easy to make a "Take it to the Bank" suggestion.

But from your description of your room's dimensions, I strongly suggest you consider at least a 135" diagonal Scope...if your mystery PJ can handle it and you can consider a shorter Throw.

To quote James T. Kirk;
"I'm laughing at the superior intellect"

http://www.invisiblestereo.com
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post #3 of 6 Old 08-06-2013, 05:26 PM - Thread Starter
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Thanks MM,

I have been following your posts for years - since I made my first screen.

I didn't want to taint the thread at the outset but was hoping for comments about curved screens having a more immersive viewing experience and possibly better light control by splashing less light around. Plus other things I don't know about. The way I plan to make the screen will make it easy to build in a vertical curve but I wasn't think of a torus.

The projector is a JVC X75 aka RS56 so no problems with lens control. I plan to make 2 screens and they will be removed when not in use.

Please preach away - even when I think I know about something, a fresh view will usually fill in some gaps. I meant to say that if I build a curved screen and use it without an anamorphic lens, I guess I would have pincushion and focus issues to deal with. I wondered if anyone thought there are benefits of having a curved screen if a lens is not used.
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post #4 of 6 Old 08-06-2013, 05:40 PM - Thread Starter
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The screen size is a work in progress. The room is multi purpose and (with removable screens) I will be setting it up for movie nights and special events. General TV viewing will be on the plasma. Seating distance is set mid-room for the plasma and larger screen heights (both screens will have the same height) are a WAF issue.

That said, bigger screens and moving the seating back are still in the mix and I am experimenting. I do believe a bigger screen creates a better movie experience and don't buy the proportional argument (a smaller screen/closer viewing distance is the same as a larger screen/increased viewing distance).

If I have enough light, why give up any contrast benefit with a shorter throw? I should be OK for lumens at 140"/max throw if I needed to.
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post #5 of 6 Old 08-06-2013, 06:53 PM
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IF you had enough light. Sadly, at 140" diagonal + and at maximum Throw distances, you do not.

As I mentioned, make the right choice as far as the Screen's coating goes, and your Contrast enhancement will far outstrip any loss of same due to increased brightness.

That Sir, has been a primary truth since MMud-SE (Silver Edition) and RS-MaxxMudd came into being, and got stupid better with the advent of Silver Fire.

Max Throw at 140" is 28" (5" retained) @ just 13 FL. Achieving deeper blacks by attenuating incoming light "BEFORE" it hits the Screen's surface is Robbing Peter to pay Paul. You do so ONLY as a last resort. The image you work with must depend upon light...not the lack thereof. It's a unfortunate testimonial to backwards logic that JVC chooses to tout low light output as a solution...which makes them the odd Mfg out these days. Also, just because they have a super wide Throw ratio does not mean the extreme end of it is usable.

At the Minimum Throw + 7" additional, your Foot Lambert jump to 20 fl. And you'll need it all since because your Zooming to achieve Scope, a good 2/5 ths of your available Lumen output is lost....poof.

While at 15' throw and 20 fl that equates to a drop of 8 fl to 12 fl off screen....at 28' and 13 fl you'd bottom out (...and I do mean crash...) at just 7.5 fl

Now all of this is based upon a 1.0 gain surface. Lets say instead you have a 1.3 gain surface that also greatly enhances perceived Contrast by deepening Blacks while retaining the perception of having pristine Whites and Dynamic Colors. I'm telling from direct experience with the RS-56 that it's JVC-caliber 90K:1 CR will look like JVC rated 250K:1.

At 11.3 gain and 15' you'd jump to 25 fl before cropping....at 28' you'd be up to 17 fl At those levels you can start to play with the Iris if you just have to.

No CaCa there! Been there, seen that a whole bunch, as has so many others.

Making yourself a viable High Gain / High Contrast screen is your best solution here....just embrace it.....cool.gif

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post #6 of 6 Old 08-06-2013, 09:20 PM - Thread Starter
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Yes, 140" at max throw is right on the limit for a unity gain screen and leaves no room for lamp ageing. Zooming past this wouldn't work.

Getting the best contrast and keeping the iris low is important for me. This equates to a low black floor which means the 'black bars' all but disappear when zooming - you really have to concentrate to make them out.

I will start a new thread about this to get some advice, but seeing as how you are here, would you recommend a white or gray/silver screen paint? I would love to try Silver Fire and MaxxMudd but can't get the ingredients here in Middle Earth (NZ).
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