Why Curved, If Anamorphic, for 720p projector? - AVS Forum
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post #1 of 42 Old 04-19-2010, 01:36 PM - Thread Starter
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Hi

My name is Alex and i'm newb newb newbie....but learn learn learning everyday. Few months ago i bought my first projector. A native 720p - Epson 705HD. Its bright for movies but great for HD sports from the satellite...and i thinks its good for first projector...

While i'm deciding which screen paint to choose, how to get the paints (cause i'm from europe) and what material to use for the screens i've start thinking about curved screens. The projector can 13'-15' throw from the screen.

I was going to ask you what makes curved screens so special but I red some threads so i'll not lose your time.

I have a few questions so I hope you'll help me

Lets start with the room! The wall where i can place the screen is 3,80m width (12' or 15" aprox.). If i cut 20cm for black borders and some free space i'll have around 3,60 or 3,50m native width for the screen. So the difference between 2.35:1 , 2.37:1 , 2.40:1 will depending from the screen height right? So i'll have to learn a little bit more how to calculate the screen.

If i go with the curved screen i'll need from a anamorphic lens right? They are so expensive that there is no way the give so much money for that! I found DIY anamorphic solutions so what do you think about them? is it worth to make my own?

So simply
- can i use anamorphic lens with my 705HD projector and use it on curved screen?
- can i use anamorphic lens just on 2:35:1(2.37:1and so on) screen?
- and i know... if there is no anamorphic lens - there would be no curved screen and so i'll have to just thinking about 16:9 screen with masking... ;/


Thanks
Alex
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post #2 of 42 Old 04-19-2010, 04:08 PM
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Hi Alex, like you said no lens then no need for a curve. A DIY lens is definately worth it in my opinion to get the most out of the experience. In which case then yes you want a curved screen to deal with pincushion. I use surplus shed prisms with an Epson HC400 720P projector and have been extremely pleased with them for a DIY solution. The are made of BK7 optical glass and have an anti reflective coating on them. For the price they beat the trophy prisms hands down. Unfortunately they are currently out of stock and usually a certain amount has to be in their order que for them to produce them.

http://www.surplusshed.com/pages/item/l9113d.html

They will ship internationally when they do get them in stock. Good luck.
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post #3 of 42 Old 04-20-2010, 12:38 AM - Thread Starter
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Thanks Oman! You and your tutorials are the reason of start thinking about all this!

And do you know what.... may be for first time i'll be the lucky guy cause i found a small company in my city which producing such a prisms. I wrote to them yesterday and get replied today. They ask me for more information like sizes and angles... so i'll paste the info from the page which gave me and hopefully....you know...

I just needed to be sure that all this gonna work with my cheap projector...

Thanks
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post #4 of 42 Old 04-20-2010, 06:04 AM
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That's great Vao, I'm glad to be of help. Be sure to post back what information you get. This may be a good source for other DIY'ers who have trouble getting the surplus shed prisms.

Good Luck.
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post #5 of 42 Old 04-20-2010, 12:45 PM - Thread Starter
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Neah.... It was too good to be true I need to purchase more then 10 prisms to get them for a good price... If I ask only two prisms the price for them will be something like 400euros. I dont know why is so expensive. May be they are mega superb turbo quality prisms.... However they told me if i purchase more then 10 the price will be under 100euros for a prisms....

So lets keep searching..... what do you think about this http://www.evright.com/showproduct.asp?p=CB8A ?

I saw somewhere ( i think it was your post Oman) that in surplus shed.com some people wait more then a year to get their lens. they are out of stock and need to be ordered more than 50 to request them in a fabric... unfortune its not a good option for me!

And something about the screen! Cause most of the tutorials are about laminate used fo the screen is it possible if i find a good thin plastic board which i'll be able to wrap it into the frame - can i paint it? Simply can i make painted curved screen with the formulas floating in board?

Take care
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post #6 of 42 Old 04-20-2010, 12:54 PM
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Yes, you can make a curved painted screen, but the result will be dependent on your painting skills. Most people like me, that don't have the painting skills, we end up with a laminate or a fabric material. There are materials like black out cloth and the Sherweave materials(more expensive) that has some acoustic transparency properties. I think you're planning too far ahead, because the curved screen(although it looks very cool) is made for an anamorphic lens setup, so without the lens, there's no use for a curved screen. I think you should find a way to land a lens first(whether DIY or commercial), then worry about the curved screen. After you acquire the lens then, you'll have a better idea of how big, and how much curvature you'd need on the screen. Take care.

PS: keep an eye out on places like eBay, Videogon, and the AVS classified section.
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post #7 of 42 Old 04-20-2010, 01:09 PM - Thread Starter
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yep thats true...DIY fishy but brave one...

my neighbour is a builder, so he has painting skills and tools whatever i want so i'm lucky from that side... but yes.... lets see first what can i do with the lens.

its much easier nowadays to buy 1080p supporting anamorphic lens format then buying anamorphic lens for 2000$ is that right?


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Originally Posted by BlazeMaster View Post

PS: keep an eye out on places like eBay, Videogon, and the AVS classified section.

thanks
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post #8 of 42 Old 04-20-2010, 01:25 PM
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I understand the issue with using a curved screen to reduce pincushion when using an anamorphic lens. My question is what happens when you slide your lens out of the way.....to watch 16x9 programming. Does this introduce pincushion or whatever the opposite is?
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post #9 of 42 Old 04-20-2010, 01:53 PM - Thread Starter
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Nice question!

I'll be watching on the opposite wall with 16:9 screen. Its smaller then the other wall (2:35) so i'll not ceiling the projector. I'm thinking of building a small table with little wheels for the projector.

yeah i know... maybe its crazy idea but i cant leave both of the walls. good memories with them...
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post #10 of 42 Old 04-20-2010, 02:13 PM
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If you remove the lens on a curved screen then Barrell Distortion will be introduced.

Something like this:
http://upload.wikimedia.org/wikipedi...ortion.svg.png
The image will curve up and down at the edges. In practice it is best to leave the lens in place and apply a 4:3 mode which will squeeze the image back down to 16:9. Then you can live with the empty space to the left and right or employ some sort of masking DIY or otherwise.

Vao, looking at the wedges on your link they will work for a DIY lens. Just be aware that they will not have anti reflective coating on them and they may introduce some stray reflections, but they are worth a shot. You will likely be very pleased with the result. Here is a DIY tutorial which is very popular.
http://www.zuggsoft.com/theater/prism.htm
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post #11 of 42 Old 04-20-2010, 04:44 PM
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Quote:
Originally Posted by AVRoberts View Post

I understand the issue with using a curved screen to reduce pincushion when using an anamorphic lens. My question is what happens when you slide your lens out of the way.....to watch 16x9 programming. Does this introduce pincushion or whatever the opposite is?

Yes it does, barrel distortion. You have hit upon the Achillees Heel of the A-lens, namely that in order to eliminate pin-cushion distortion of the 2.35 image you need a curved screen, but a curved screen will now distort the 16:9 image. You can eliminate the 16:9 barrel distortion by leaving the A-lens in place and showing 16:9 in 4:3 mode (33% horizontal compression), but then you lose 33% of the horizontal resolution of the 16:9 image. So whatever you gained for the 2.35 image by using the A-lens is now lost on the 16:9 image. Take your pick, distortion of the 16:9 or 33% loss of resolution., or just simplify things by zooming for 2.35 (which produces zero distortion on a flat screen) and your 16:9 is totally uncompromised.
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post #12 of 42 Old 04-23-2010, 03:32 PM - Thread Starter
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Quote:
Originally Posted by oman321 View Post

Vao, looking at the wedges on your link they will work for a DIY lens. Just be aware that they will not have anti reflective coating on them and they may introduce some stray reflections, but they are worth a shot. You will likely be very pleased with the result. Here is a DIY tutorial which is very popular.
http://www.zuggsoft.com/theater/prism.htm


neah i dont hurry up. I prefer these from surplushed... However how do you know if the prisms have AR coating or not. By description or the picture? I saw some new prisms with AR2 or something and Universal Astigmatism Correction Element which is interesting...
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post #13 of 42 Old 04-25-2010, 07:13 PM
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The AR2 that you're talking about should be the ones made by the guys from the HTB guys, right? If so, then yes, their AR2 will have anti reflection coating.
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post #14 of 42 Old 04-26-2010, 01:00 AM
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Quote:
Originally Posted by taffman View Post

You can eliminate the 16:9 barrel distortion by leaving the A-lens in place and showing 16:9 in 4:3 mode (33% horizontal compression), but then you lose 33% of the horizontal resolution of the 16:9 image.

It is actually just 25% compression, not 33%. 1920 x 0.75 = 1440. 1440 x 1.33* = 1920.

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I love my Constant Image Height system!
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post #15 of 42 Old 07-11-2010, 07:56 AM - Thread Starter
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So the anamorphic prisms are back in stock on surplus! Before finally take my decision I want to ask some question!

Projectors like Panasonic AE4000 supporting lens memory does doing the same job like the anamorphic prisms on curved screen!? I mean if I buy the anamorphic prisms and install 2:35:1 curved screen will I need from the prisms if one day I buy 1080p anamorphic ready projector?

And does this prisms fully AR coated spoil the quality somehow?

Thanks
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post #16 of 42 Old 07-11-2010, 05:00 PM
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I haven't seen any I'll effects from the AR coating on the prisms. Refer to post 10 above in reference to using a projector with a curved screen and no lens. It will cause barrel distortion.

If you anticipate getting a Panasonic in the future and plan to use it without the lens I would build or make a flat screen or you can still use the lens with your projector also. Good luck.
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post #17 of 42 Old 07-12-2010, 07:29 AM
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Keep in mind the size of the surplus shed prisms vs the size of the post projector lens image size. Meaning, you can't use these prisms if you plan on having the projector mounted at a distance that would require a good bit of zoom.

-Sean
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post #18 of 42 Old 07-12-2010, 10:01 AM
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This is true, placement is important. Even though they are small, I do have a decent amount of range in my manual zoom. If I remember correctly I have about 1/3 of the zoom range to play with. This is aided by the fact that I can place the 1st prism practically up against the projectors lens. I have about a 14 foot throw from the projectors lens to a 120" scope screen.
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post #19 of 42 Old 07-13-2010, 04:33 AM - Thread Starter
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How can I calculate this?

My projector is Epson Home Cinema 705HD and the screen will be 3.75m width. The distance - 5.3m (avg. 17.3')

And my source is a htpc, not blu-ray player. Is that a problem?
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post #20 of 42 Old 07-13-2010, 04:46 AM
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3.7m width might be too big for a projector like the 705HD. Beside that you'll notice the screendoor of the panels going with such a big screen.
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post #21 of 42 Old 07-13-2010, 07:08 AM
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That issue aside, you have to determine the size of your 16:9 image. It would seem that your 16:9 image is a screen which would be about 120-125 inches diagonal or a width of about 115 inches. According to the manual to get an image that size you need a throw distance between 111-167 inches or 281-424 cm.

At 17' you are at about 204 inches for a throw which will produce an image of at least 150" at minimum zoom. If you can bring up a couple of feet or so you may be ok.
Manual:
http://files.support.epson.com/pdf/p.../plhc705ug.pdf
If you are using the projector at this distance now for a comprabable 16:9 screen I would give it a shot, the prisms wont make the image look anymore pixelated, but that would be a big screen.
Good luck.
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post #22 of 42 Old 07-13-2010, 08:54 AM - Thread Starter
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Wow.. there are so much things to think... Thanks for your patience!

So the whole wall is 3.80m width. Lets say the screen will be 3.65 because of the black borders (6cm each one or something) and 1.5cm free space from the both sides!
The max throw distance i can get is not 5.3m like i said but 4.90m. So yeah i can cover 281-424 cm. I watched two movies on that wall (because usually i watch on the opposite 110") and there was no problem... i covered the whole wall...
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post #23 of 42 Old 07-13-2010, 12:22 PM
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My response was assuming that you want to use the Surplus Shed prisms which are small. If you need to use more than 1/3 of the zoom which your projector offers you then you may have a difficult time for the image to fit properly in the light path. Eventually the image will start to vignette which means it will start getting cut off because it simply doesn't fit thru the prisms.

Basically when using prisms you want the image to be as close to minimum zoom as possible so you won't have a problem and then the projector gets moved back of forth to hopefully fill the screen properly. Luckily you still have a little room to manipulate the zoom if you need to.
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post #24 of 42 Old 07-14-2010, 05:53 PM
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Yeah, I'm using a DIY lens using 6"x8" prisms, which are large, and I'm at around a 1.85x zoom and its close to the limits. Placement of PJ, lens shift, and distance from screen are all factors that need to be thought of when deciding on lens and screen size. When you are at the extremities of the lens/screen/projector setup, you need a curved screen because pincushion is more noticeable.

-Sean
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post #25 of 42 Old 07-18-2010, 05:41 AM - Thread Starter
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So after all this good and bad things you think I'll be able to set everything in normal?

Let see if I understand correctly!
This is a 4.8m throw distance in my room on Native apect ratio. (I still don't have the CIH)


So I need to move the projector closer to the wall and look like that


And then place the lens front of the lamp and hopefully voala!?
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post #26 of 42 Old 07-18-2010, 09:22 AM
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Do you have your PJ zoomed all the way back? To clarify, you are not using any zoom at all correct? If you are using the zoom, then moving the PJ closer to the screen wall is only going to hurt the situation.

If you are saying that using no zoom at all is giving you a 16:9 image that is bigger than you want your CIH screen to be, then yes, move it closer to the screen wall. Again, the goal is to get the screen size you want using as little zoom as possible.

-Sean
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post #27 of 42 Old 08-29-2010, 03:42 AM - Thread Starter
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Hello!

So i tested today and here is the result!

First i draw example screen on the wall just with a pencil. Its 366cmx155cm... may be i'm wrong with a few cm...

Well I get minimum zoom projecting on the 380cm throw distance which fits the screen. Any moving closer to the screen I'll play with the zoom. Also I got 60cm-60cm free space from the both side hopefully will be enough.

Here is a pic

What do you think? Will this work with the lens surplus?
LL
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post #28 of 42 Old 09-06-2010, 01:20 PM - Thread Starter
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anyone?

does the surplus prisms will work in my situation?
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post #29 of 42 Old 09-06-2010, 04:17 PM
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Quote:
Originally Posted by Vao View Post

So after all this good and bad things you think I'll be able to set everything in normal?

Let see if I understand correctly!
This is a 4.8m throw distance in my room on Native apect ratio. (I still don't have the CIH)


So I need to move the projector closer to the wall and look like that


And then place the lens front of the lamp and hopefully voala!?

Your top image is how you should set up the projector if using a VC lens only. The anamorphic lens is what optically stretches the image, not the projectors zoom.

Quote:
Originally Posted by Vao View Post

anyone?

does the surplus prisms will work in my situation?

If your throw is long enough, then yes. How ever, you need to begin with the 16:9 image at the same height as the Scope screen.

Mark Techer

I love my Constant Image Height system!
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post #30 of 42 Old 10-15-2010, 05:30 PM
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Hi CAVX,

Sorry to interrupt with a newb question.

Can a CIH 2.35 setup w/ fixed anamorphic lens be shelf mounted for retro-reactive projection (~head height) or do PJs using anamorphic lenses always need to be ceiling mounted? Is there a general rule there? Thank you, kindly.
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