Ok, so I got the screen put together, and movies look fairly decent. But I am experiencing some bowing top and bottom. Does this mean I'd have to build a curved screen to eliminate it, or do I have other options?
mpotoka said:
You have to put the prisms perpendicular to the light beam from the PJ. If it's ceiling mounted, tilt the prisms DOWNWARD. You have to play with the angle a bit since it depends on your PJ. A curved screen helps but you can get along pretty good without it.
Bud
I have been tilting them downward, but it is at the point now where if I tip it downward more, the top of the screen becomes a much bigger smile. I've kind of found the happy medium, and very slightly defocused the middle of the screen to gain some focus on the edges.
I'm sure a curved screen would work well for me, but right now I'm just happy with how it is. I'll run it through some DVE tonight and then post a few pictures and I'll see what you guys think (or see)
Mike
I'm sure a curved screen would work well for me, but right now I'm just happy with how it is. I'll run it through some DVE tonight and then post a few pictures and I'll see what you guys think (or see)
Mike
I would definitely agree that proper geometry is key, but I keep hearing about this bowing and I am worried. Is this bowing an inherent quality of these lens and projections? I mean, if I project my Hitachi TX200 dead centre on the screen and get the prisms as perpendicular as possible to the light beam/projector/screen setup, shouldn't it look fairly square geometry wise? Are any other retail lens any different?
Unfortunately, the way my projector is set up, I have to construct something just to test the prisms. I have no way to place them in front right now. I will give it a try and see what happens.
Unfortunately, the way my projector is set up, I have to construct something just to test the prisms. I have no way to place them in front right now. I will give it a try and see what happens.
morkys said:
I've heard that even the all mighty ISCO III needs to be titled, so yes it would appear so...
Mark
Panamorph 752 and AR's between 1.78 and 2.37?
Isn't it true that a Panamorph 752 only does a 33% vertical compression so that you cannot use it for movies like Apocalypse Now at 2.0:1 and movies like Tron and Lawrence of Arabia at 2.20:1?
With the prisms, we can do any width, but the fixed panamorph cannot be used for anything other than 2.37:1..correct? If this is the case, all the more reason not to bother with a Panamorph 752?
Isn't it true that a Panamorph 752 only does a 33% vertical compression so that you cannot use it for movies like Apocalypse Now at 2.0:1 and movies like Tron and Lawrence of Arabia at 2.20:1?
With the prisms, we can do any width, but the fixed panamorph cannot be used for anything other than 2.37:1..correct? If this is the case, all the more reason not to bother with a Panamorph 752?
Re: Panamorph 752 and AR's between 1.78 and 2.37?
The point is, even our prisms based lenses are still centred around 33% stretch or compression. The number offsets the smount of squeeze or stretch applied to the video signal for anamorphic enhanced video.
The only true way to have multiple AR control is to employ an external scaler, as well as have varible stretch HE lens, as well as varible side masking.
In perfect world, the screen would cater for all ARs including some at 2.76:1. However this is video after all, so some compromise must be reached. Given that the majority of films will work on our CIH systems, you have to take into consideration the effort that goes to making a true CIH system, and the expense - which is sadly above most of us here...
Mark
morkys said:
The point is, even our prisms based lenses are still centred around 33% stretch or compression. The number offsets the smount of squeeze or stretch applied to the video signal for anamorphic enhanced video.
The only true way to have multiple AR control is to employ an external scaler, as well as have varible stretch HE lens, as well as varible side masking.
In perfect world, the screen would cater for all ARs including some at 2.76:1. However this is video after all, so some compromise must be reached. Given that the majority of films will work on our CIH systems, you have to take into consideration the effort that goes to making a true CIH system, and the expense - which is sadly above most of us here...
Mark
Well, I am employing an external scaler. I will take the 16:9 letterboxed image and fill the screen vertically. I was hoping I could use the prisms to return the full 16:9 to whatever the aspect ratio was, be it 2.0:1 or 2.20:1 or 2.37/2.40:1. I guess I will see how it goes. If I cannot get the proper aspect ratio for films between 1.78 and 2.37 then I will miss many films, including the main one I wanted to do, Lawrence of Arabia.
The first time I saw the Prismasonic H1200 was with a set up that ran HTPC, VP 30 and the owner would do exactly that - custom each AR to be perfect. Time consuming, and assuming that the geometry is truely correct, if perfection is your goal, then why not...
I checked my 300+DVDs and only have 3 that are in between (wider than) 1.85 and (less than) 2.35, so for me it is not worth the effort...
I did the maths and found out that I loose up to 8% (4% top and 4% bottom) anyway from the combination of my projector and the anamorphic 33% process, so it is not that important to me given that there is really not that much I can do about...bassically a film has to be 2.55:1 before I am going to see any letterboxing on my set up, so not likely to happen except for a very few like Lawrence of Arabia which if you can track down the true AR is actually 2.76:1, not 2.20:1...
Mark
I checked my 300+DVDs and only have 3 that are in between (wider than) 1.85 and (less than) 2.35, so for me it is not worth the effort...
I did the maths and found out that I loose up to 8% (4% top and 4% bottom) anyway from the combination of my projector and the anamorphic 33% process, so it is not that important to me given that there is really not that much I can do about...bassically a film has to be 2.55:1 before I am going to see any letterboxing on my set up, so not likely to happen except for a very few like Lawrence of Arabia which if you can track down the true AR is actually 2.76:1, not 2.20:1...
Mark
Yeah, I figured that about Lawrence of Arabia, but the thing is this. I researched which was the best looking Lawrence of Arabia and it was the Superbit version, which also has DTS. That is fine, but the version is still labeled as 2.20:1. I will try to clarify that.
Still, as I understand it, I can take the 2.0 and 2.20:1 movies and fill my 16:9 vertically, and then use the prisms to restore the aspect ratio. For any movie over 2.37:1, that is fine, that just means I will see black bars on the 2.37:1. It's better than severely letterboxed 16:9..right?
Purely for arguments sake, here is the link showing all the dvd versions of Lawrence of Arabia:
http://www.dvdcompare.net/comparisons/film.php?fid=462
They are all 2.20:1!
What is up with that? I recall hearing that the actual movie is 2.76:1 or something like that. So the dvd's are all screwed?
Still, as I understand it, I can take the 2.0 and 2.20:1 movies and fill my 16:9 vertically, and then use the prisms to restore the aspect ratio. For any movie over 2.37:1, that is fine, that just means I will see black bars on the 2.37:1. It's better than severely letterboxed 16:9..right?
Purely for arguments sake, here is the link showing all the dvd versions of Lawrence of Arabia:
http://www.dvdcompare.net/comparisons/film.php?fid=462
They are all 2.20:1!
What is up with that? I recall hearing that the actual movie is 2.76:1 or something like that. So the dvd's are all screwed?
Interesting, so why do the scope "experts" at AVS keep referring to this film as having an AR or 2.76:1?
I have not even seen the film is widescreen, so when I saw the initial DVD release as 2.20, I just excepted that as correct and was kind of disappointed that an even wider version might be available...
Mark
I have not even seen the film is widescreen, so when I saw the initial DVD release as 2.20, I just excepted that as correct and was kind of disappointed that an even wider version might be available...
Mark
Mark, I've been watching this thread with great interest. I ordered some J25 Prisims and hopefully will be getting here soon. I have an Infocus X1 projector which is ceiling mounted. As I understand, when I get the prisms I will have to follow the path of projection remaining perp. with the image. This may mean even adding some tilt to the prisims to prevent center bowing right? Even after all said and done, would you, in your professional opinion recommend building a torus screen? I won't lie Mark, my math sucks, how would I figure out the bow of the screen. Sorry to ask so many dumb question, I just trying to learn. Thanks
aad1972 said:
You DO realise the X1 is a native 4:3 projector so you will not get 2.37 stretch. I know, I have one(and my HD72)
Bud
Your best bet is to start with a flat screen and see what the projector/lens combo does first. Basically, curved screens (including torus) are there to correct errors introduced by the lens. So you need to identify the problems first or you could introduce more problems than you solve.
My projector (SONY HS3) is an extremely short throw device. Therefore when used with a HE lens, the edge distrotions that occur are going to be way worse than with say SONY's HS20.
Right now I have a curved screen, but the dip in the centre is just 2" across 8 foot of width, so very shallow, yet this is all I needed to get a straight bottom edge.
The sides are not too bad either. Tilting the lens (whole case) has worked best for me. Basically just 5 degrees upward tilt (projector is shelf mounted at this time) has virtually straightened out the side bowing and reduced what was really bad keystone, even though the beam is straight without the lens in place.
I have found that tilting the rear prism made a difference to the right side as well, but holding it place has proved a little more difficult than first appeared. As I tightened down the lid, the prisms moved back into the original position.
Anyway, it is looking good right now, with only a very slight right side "warp" which is only really noticeable in the 16:9 (4 x 3 + lens) mode...
Mark
My projector (SONY HS3) is an extremely short throw device. Therefore when used with a HE lens, the edge distrotions that occur are going to be way worse than with say SONY's HS20.
Right now I have a curved screen, but the dip in the centre is just 2" across 8 foot of width, so very shallow, yet this is all I needed to get a straight bottom edge.
The sides are not too bad either. Tilting the lens (whole case) has worked best for me. Basically just 5 degrees upward tilt (projector is shelf mounted at this time) has virtually straightened out the side bowing and reduced what was really bad keystone, even though the beam is straight without the lens in place.
I have found that tilting the rear prism made a difference to the right side as well, but holding it place has proved a little more difficult than first appeared. As I tightened down the lid, the prisms moved back into the original position.
Anyway, it is looking good right now, with only a very slight right side "warp" which is only really noticeable in the 16:9 (4 x 3 + lens) mode...
Mark
ACK! FAINT REFLECTIONS!!!
Okay, I'm getting some stray reflections every now and then during movies. They seem to show up during dark scenes where there is a stark light object on one side of the screen or the other. The image basically mirrors itself on the opposite side of the screen. It is faint in most cases, but distracting to me none the less.
Is there any way to get rid of these stray reflections?
Thanks!
Paul
Okay, I'm getting some stray reflections every now and then during movies. They seem to show up during dark scenes where there is a stark light object on one side of the screen or the other. The image basically mirrors itself on the opposite side of the screen. It is faint in most cases, but distracting to me none the less.
Is there any way to get rid of these stray reflections?
Thanks!
Paul
It's the reflection off 1 prism onto the other. These aren't anti-reflective coated like glasses. Don't think you can do much, do you have the inside housing blacked out?artbypaul said:
Bud
Yep, everything is blacked out around the prisms. I guess it's not too bad, nobody has commented on it. It usually only lasts for a few seconds normally. But you're absolutely correct about not being a fixable problem as the image is obviously bounced off the facing prism sides which can't be covered.
I think Mark looked into that. Considering the cost to coat a pair of glesses, this size may be REALLY expensive. Doesn't hurt to look around though.
Here's a question for people, how have you got your prisms in the housings? Are they secured? (So far i've broken 4 prism from having them fall out of my tilted housing, not secured in yet). I'm still fighting wether to have them fixed in place or rotating...
Thinking i'll go for FIXED for no(so more don't break) and retro-fit for pass thru later.
Bud
Here's a question for people, how have you got your prisms in the housings? Are they secured? (So far i've broken 4 prism from having them fall out of my tilted housing, not secured in yet). I'm still fighting wether to have them fixed in place or rotating...
Thinking i'll go for FIXED for no(so more don't break) and retro-fit for pass thru later.
Bud