Just got my French Prisms - Page 11 - AVS Forum | Home Theater Discussions And Reviews
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post #301 of 322 Old 09-03-2010, 01:19 PM
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Hi all, thanks for the replies.
I must apologise, I just re-read my post and realised I forgot to mention that the CA I see is when looking at a test pattern, specifically the HCFR Anamorph one. The CA isn't usually that noticeable during normal film viewing, except perhaps for CGI stuff. I believe focus/astigmatism is a bigger issue for me.

I was just adding to what a couple of others here have said about the french prisms as it seems a few people get the CA on the left hand side only, perhaps the un-equal prisms factor in to this...
Taking Mark's advice I have moved the projector about as central as I can determine using rudimentary measures, (it would be useful if I had some sort of giant set square :-) but I still get the CA on the left side only, I will try adjusting the actual prisms again, but I don't hold much hope as that was where I started...

Back to focus, are there any astigmatism correction devices out there suitable for a DIY lens, including those based on french prisms?

Thank again guys
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post #302 of 322 Old 09-03-2010, 07:52 PM
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Just take a look on the UACE of Anamorphic Research. That's what you need.
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post #303 of 322 Old 09-06-2010, 01:35 AM
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Originally Posted by Widlarizer View Post

Just take a look on the UACE of Anamorphic Research. That's what you need.

Thanks Widlarizer, I'll check it out, I had come across it before and suspected it may only be suitable for their lens? I guess that if their solution is based on 2 prisms then theoretically it shouldn't make any difference which prisms are used...
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post #304 of 322 Old 02-06-2017, 03:28 AM
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hello , where i can buy this glass ? thanks
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post #305 of 322 Old 04-10-2017, 09:11 AM
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I also am thinking about DIY anamorphic lens of some kind.
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post #306 of 322 Old 04-14-2017, 01:45 AM
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Just curious, if it were possible to get large plastic cylindrical elements (say about $200USD), how many would buy them?

Mark Techer

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post #307 of 322 Old 12-26-2018, 05:10 PM
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Just posted about my screen build in the DIY section for that: https://www.avsforum.com/forum/110-d...l#post57329326


I included my simple case for the french prisms in that post. I glued black felt to some 1" redwood boards, and built a simple encasement. The prisms are held by the pressure of the top board, being screwed down. This allows to shift the prisms a bit (with white gloves) to make fine adjustments, but they are held in place pretty securely.


I ordered them in early December for $165, but then I noticed they were on sale for $125 a few days later, so keep your eyes peeled. They are a pretty good deal either way. https://www.surplusshed.com/pages/item/L9113D.html
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post #308 of 322 Old 02-08-2019, 12:00 PM
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Quote:
Originally Posted by scarabaeus View Post
Just posted about my screen build in the DIY section for that: https://www.avsforum.com/forum/110-d...l#post57329326


I included my simple case for the french prisms in that post. I glued black felt to some 1" redwood boards, and built a simple encasement. The prisms are held by the pressure of the top board, being screwed down. This allows to shift the prisms a bit (with white gloves) to make fine adjustments, but they are held in place pretty securely.


I ordered them in early December for $165, but then I noticed they were on sale for $125 a few days later, so keep your eyes peeled. They are a pretty good deal either way. https://www.surplusshed.com/pages/item/L9113D.html
$125 I might be able to swing, but $165 seems too high for my cheap projector. I swear the first time I researched this, it was only $60 for a pair of trophy prisms.

I have a couple questions for prism owners.

My story first:
I have an older 720p short throw Sharp projector which I still love. The lens is 10'8" from the screen and throws a 7'8" wide 16:9 screen. At 16:9, the picture is beautiful, bright, and I'm still content with the resolution. When we watch 2.35:1 movies the reduction in size and brightness is too much so I have to bump the brightness up through the settings to the point where you see the gray bars above and below, and the screen is just shy of a size I would be content with. I project on a gray wall that is a little over 10' wide. Nobody else seems to mind the gray bars or the size, but I do.

I just finished the basement rebuild, and the plan was to upgrade to a brighter higher contrast projector that could zoom out to fill the 10' width, but I want to hold off for a few reasons. This projector still works well and has a lot of life in it, the basement cost a lot so money is tight at the moment, and I really feel like projectors are taking a leap right now with LED light sources 4K and HDR, and I feel like a little waiting will enable me to get a lot more for my money. The biggest reason though, is that it seems like there are no short throw projectors anymore, and I'm buying time hoping that someone steps up to fill the gap between ultra short throw and standard.

With all this in mind, I was hoping for a really cheap anamorphic solution to use in the interim, thinking that I might only use it for 6 months and then upgrade the projector. The other part of me thinks that having an anamorphic lens might allow me to hold off longer, or even have the option to buy a standard throw projector and still fill my screen width.
So my questions for prism owners are:
- With the french prisms (or trophy prisms for that matter), does the picture seem much brighter since you are using the full picture, or will the loss of brightness from going through the prisms essentially be a wash with the gain of using the full panel?
- Will the CA or astigmatism be too substantial for my 10'8" throw distance? Issues like minor pincushion or a slightly soft focus don't bother me, but if everything on the edges is always going to seem out of focus, that probably would. If I am only likely to notice during the credits but everything is still legible, I consider that a fair trade off.
- After reading my story and knowing your experience with an anamorphic screen do you think it is definitely worth diving into, or maybe not?
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post #309 of 322 Old 02-09-2019, 09:24 AM
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Hi, I'm just at the beginning of my prism journey, but I'll try to answer you as much as I can.


Quote:
Originally Posted by rdcollns View Post
$125 I might be able to swing, but $165 seems too high for my cheap projector. I swear the first time I researched this, it was only $60 for a pair of trophy prisms.

The Surplus Shed Prisms are optically coated, unlike trophies, which reduces inner reflections. I get very dim reflections in only some parts of the image.


Quote:
So my questions for prism owners are:
- With the french prisms (or trophy prisms for that matter), does the picture seem much brighter since you are using the full picture, or will the loss of brightness from going through the prisms essentially be a wash with the gain of using the full panel?
- Will the CA or astigmatism be too substantial for my 10'8" throw distance? Issues like minor pincushion or a slightly soft focus don't bother me, but if everything on the edges is always going to seem out of focus, that probably would. If I am only likely to notice during the credits but everything is still legible, I consider that a fair trade off.
- After reading my story and knowing your experience with an anamorphic screen do you think it is definitely worth diving into, or maybe not?

The picture will be more dim, since you are spreading the light from the projector over a larger area. I don't notice much dimming by the prisms themselves.


The CA, as far as I know, is not related to the overall projection distance, it's an angular aberration. Because of that, of course, it is more noticeable the larger your screen size is.


I think it's definitely worth it, especially if you are mainly watching widescreen movies. I leave the prism in place, and use the Oppo 203, set up for a fixed 21:9 aspect ratio, as the scaler. That has the advantage that none of the blu-ray menus or subtitles are cut off.


For other sources and content, your experience might be less optimal. 1.85:1 movies still have slim letterbox bars, in addition to the side bars which you have with 16:9 content. For anything 2.20:1 and above, I crop it to 2.40:1 (2.55:1, again, has small letterbox bars, but takes up the whole width). 2.00:1 (Netflix) is the worst, either you lose a bunch of content at the top and bottom, or you have some serious windowboxing.


But 2.40:1 movies are just so impressive with a system like this!
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post #310 of 322 Old 02-09-2019, 10:38 AM
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Quote:
Originally Posted by scarabaeus View Post
Hi, I'm just at the beginning of my prism journey, but I'll try to answer you as much as I can.





The Surplus Shed Prisms are optically coated, unlike trophies, which reduces inner reflections. I get very dim reflections in only some parts of the image.





The picture will be more dim, since you are spreading the light from the projector over a larger area. I don't notice much dimming by the prisms themselves.


The CA, as far as I know, is not related to the overall projection distance, it's an angular aberration. Because of that, of course, it is more noticeable the larger your screen size is.


I think it's definitely worth it, especially if you are mainly watching widescreen movies. I leave the prism in place, and use the Oppo 203, set up for a fixed 21:9 aspect ratio, as the scaler. That has the advantage that none of the blu-ray menus or subtitles are cut off.


For other sources and content, your experience might be less optimal. 1.85:1 movies still have slim letterbox bars, in addition to the side bars which you have with 16:9 content. For anything 2.20:1 and above, I crop it to 2.40:1 (2.55:1, again, has small letterbox bars, but takes up the whole width). 2.00:1 (Netflix) is the worst, either you lose a bunch of content at the top and bottom, or you have some serious windowboxing.


But 2.40:1 movies are just so impressive with a system like this!
Thanks for throwing in your opinion. This helps a lot, especially all the information on the last question related to each aspect ratio. We watch a lot of Netflix, and I'm surprised they use a different ratio. But for whatever reason we tend to watch Netflix on a 55" LCD upstairs. The projector really seems destined for just movies and sports with general TV watching upstairs. I think you've convinced me to go for it, but the cost will be a lot more palatable for my wife if I wait for a sale or possibly my birthday.

I love the box you built for the prisms. So perfectly simple.
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post #311 of 322 Old 02-11-2019, 07:40 AM
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Quote:
Originally Posted by rdcollns View Post
Thanks for throwing in your opinion. This helps a lot, especially all the information on the last question related to each aspect ratio. We watch a lot of Netflix, and I'm surprised they use a different ratio. But for whatever reason we tend to watch Netflix on a 55" LCD upstairs. The projector really seems destined for just movies and sports with general TV watching upstairs. I think you've convinced me to go for it, but the cost will be a lot more palatable for my wife if I wait for a sale or possibly my birthday.

I love the box you built for the prisms. So perfectly simple.

Thank you!


I just noticed, they are on sale for $95 right now: https://www.surplusshed.com/pages/item/L9113D.html
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post #312 of 322 Old 02-13-2019, 02:12 PM
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Originally Posted by scarabaeus View Post
Thank you!


I just noticed, they are on sale for $95 right now: https://www.surplusshed.com/pages/item/L9113D.html
You sir, are my hero. I'm buying a set. Anything you would change about your enclosure?
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post #313 of 322 Old 02-13-2019, 06:20 PM
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Originally Posted by rdcollns View Post
You sir, are my hero. I'm buying a set. Anything you would change about your enclosure?

Sure, you are welcome! I suppose the more they sell, the longer they will keep making them and have them in stock. Good for all of us.



I would like to change the top of mine. Right now I have 4 normal screws to tighten the vertical compression, but something with less physical impact would be better. I though of maybe wing nuts, or butterfly closures down the sides.


I once had tried to nudge the prisms a bit, and didn't bother to loosen the screws, but that lead to the prisms not being exactly vertical. And that causes more pincushion distortion. I had to take the enclosure down, loosen the screws, and re-tightening them without moving the prisms to fix that.


Also, make sure your length (front to back) of the boards matches the drawing's value of 114.8mm closely, otherwise your light beam will be cut off. Rather have it a bit shorter and a corner of the prism hang over the edge, than too much board in the front blocking your light.
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post #314 of 322 Old 02-17-2019, 12:00 AM
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You sir, are my hero. I'm buying a set. Anything you would change about your enclosure?
I'm a little giddy at the moment. I just watched my first anamorphic film. No black bars above or below, 120" wide screen from 126" throw distance, focus was clean, CA is present but you really have to know it is there to care about it. My screen is twice as bright and feels twice as large.

That being said, I have a massive curve (pincushion) at the bottom of the screen. I have a feeling I can minimize it, but the few things I have tried don't seem to make a difference. I am ceiling mounted, the curve is up in the middle of the bottom of the screen.
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post #315 of 322 Old 02-17-2019, 12:09 AM
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Quote:
Originally Posted by rdcollns View Post
Quote:
Originally Posted by rdcollns View Post
You sir, are my hero. I'm buying a set. Anything you would change about your enclosure?
I'm a little giddy at the moment. I just watched my first anamorphic film. No black bars above or below, 120" wide screen from 126" throw distance, focus was clean, CA is present but you really have to know it is there to care about it. My screen is twice as bright and feels twice as large.

That being said, I have a massive curve (pincushion) at the bottom of the screen. I have a feeling I can minimize it, but the few things I have tried don't seem to make a difference. I am ceiling mounted, the curve is up in the middle of the bottom of the screen.
Here is a photo of the prisms quick clamped in position and the screen.
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post #316 of 322 Old 02-17-2019, 12:11 AM
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Quote:
Originally Posted by rdcollns View Post
Quote:
Originally Posted by rdcollns View Post
Quote:
Originally Posted by rdcollns View Post
You sir, are my hero. I'm buying a set. Anything you would change about your enclosure?
I'm a little giddy at the moment. I just watched my first anamorphic film. No black bars above or below, 120" wide screen from 126" throw distance, focus was clean, CA is present but you really have to know it is there to care about it. My screen is twice as bright and feels twice as large.

That being said, I have a massive curve (pincushion) at the bottom of the screen. I have a feeling I can minimize it, but the few things I have tried don't seem to make a difference. I am ceiling mounted, the curve is up in the middle of the bottom of the screen.
Here is a photo of the prisms quick clamped in position and the screen.
Projector
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post #317 of 322 Old 02-19-2019, 09:19 AM
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i cant get the photo to work. i think i would like to do this as well if they go on sale again. did it seem any brighter with the lens? just saw you said it was brighter
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post #318 of 322 Old 02-25-2019, 11:02 AM
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Originally Posted by scarabaeus View Post
Thank you!


I just noticed, they are on sale for $95 right now: https://www.surplusshed.com/pages/item/L9113D.html
That would have been a great deal. Do they go on sale often?
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post #319 of 322 Old 02-25-2019, 11:24 AM
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That would have been a great deal. Do they go on sale often?

They seem to have sales once in a while. You can create an account and opt in to their email mailing list where they announce sales.
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post #320 of 322 Old 02-25-2019, 11:31 AM
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Quote:
Originally Posted by rdcollns View Post
That being said, I have a massive curve (pincushion) at the bottom of the screen. I have a feeling I can minimize it, but the few things I have tried don't seem to make a difference. I am ceiling mounted, the curve is up in the middle of the bottom of the screen.

Try to angle the whole prism assembly down a bit (carefully, since your prisms are not yet clamped down...) That seems to make the pin cushion less severe, and at the least you will be able to balance it between top and bottom.
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post #321 of 322 Old 04-09-2019, 05:51 AM
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i cant get the photo to work. i think i would like to do this as well if they go on sale again. did it seem any brighter with the lens? just saw you said it was brighter
I missed your question before. The whole reason I started this was brightness. 16:9 films looked great, but 2:35 films were unwatchable because they were so dark . I really want my next projector to be LED or laser, but they aren't quite down to my price range yet, so I'm going to stretch my current projector for a little longer. The prisms create a much brighter image. It feels like it's twice as bright, and it is so much more enveloping. I've had projection screens ranging from 6' wide to 10' for a long time. This is only a foot wider at 11', but it feels so much bigger. The best part is that we have a brand new 55" 4K LED TV upstairs, but everyone wants to go downstairs to watch movies on a 10 year old 720p projector. I can't wait to upgrade, but I'll probably keep the prisms in place when I do.
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post #322 of 322 Old 04-27-2019, 07:56 AM
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What are these universal astigmatism corrector elements? Some plano convex cylindrical lens (if yes what radius of curvature)? I am looking for replacement when they are not available to buy.
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