DIY anamorphic lens - Page 14

JudeBarnes · 9th January 2003, 10:22 PM

I see so you send the projector full panel and then expand it to it's proper ratio, rahter than compress. I can see why this would be preferable in some isntances, for example, if the projector were much closer to the screen, and need to expand the picture larger ! But, I'm curious what you do to your source image exactly to get it squeezed without losing pixles? Do you turn the projector on it's side???

Jonathan M · 9th January 2003, 10:33 PM

Anamorphic PAL DVD material is 720x576 in resolution.

I think that an 800x600 panel, cropped to 720x576 would thus produce the exact pixels as are present on the DVD.

Now, project that image through an anamorphic lens (One for 16:9, and one for 21:9 etc.) and you have a superb image. You can choose whether to compress vertically or expand horizontally as needed. No rescaling digitally taking place. Just optics. You also only need an 800x600 sized screen.

Now, I am assuming that 2.35:1 DVDs are recorded anamorphically, so that the image takes up all the available vertical pixels. If this is incorrect, then at least it would work for 1.85:1 images.

Obviously if you want to view a higher res image it'll start degrading quality, but for DVD's, I can't think of anything better.

Just a thought

Axeman · 9th January 2003, 11:17 PM

I believe 2.35:1 movies are encoded anamorphically, but with the same ratio as regular widescreen movies. not all the vertical pixels get used, but more than if there was no optical compression in use.

Lifter · 10th January 2003, 01:24 AM

Almost all DVD movies have anamorphic encoding on them. Some movies are 1.85:1, and some are 2.35:1. Movies that are 2.35:1 are actually filmed w/ an anamorphic lens to fit on 35mm film frames (which normally has a 1.85:1 aspect ratio). Then when projected, the theatre's projector will switch to an anamorphic lens to reverse the effect, thus making it wider. That's why 2.35:1 movies are refered to as "anamorphic widescreen".

As far a DVD's go, anamorphic has a different meaning. Both 1.85:1 and 2.35:1 movies are anamorphicly encoded on most DVDs so that it will fit on a 16:9 (about 1.78:1). Usually, 1.85:1 movies have the sides croped just a slight amount, while 2.35:1 movies have black bars on the top and bottom (although they're of course not as big as they would be on a letterbox 3:4 picture).

Michael F T · 10th January 2003, 04:21 PM

I like a bigger image and that's why I expand.
The way I did it is just turn the prisms on their side. Instead of the point of the prisms putting vertically, they point to horizontally.

It's literally turning the whole lens on it's side.
I had a problem with air bubbles but since I didn't seal it up, I used a copper wire to pop them all.

I also used Walgreens Mineral Oil and it looks great.
Currently, I am using Plexi-glass and lose some of the brightness gains, but I still like it more since I don't have the black bars.

BTW - to view a 2.35 movie with all of the pixels you need a scaler to zoom in on only the picture because the 2.35 DVDs have the black bars encoded on the dvd.

JudeBarnes · 10th January 2003, 04:51 PM

Even though you say you lose some brightness overall I think you are gaining some brightness, too, by losing the black bars and filling it with pixels instead.
I definitely CANNOT make my image bigger. If I do I will see the artifacts already inherent even more. The compression of the image has eliminated the two most pesky problems for HT viewing for my wife and I:
1. The black (grey) bars/lightspill
2. The horizontal scanline artifacts which occur on most LCDs with rapid vertically moving objects.

ccarrigan · 13th January 2003, 07:35 PM

Where does everyone get your glass? Will Home Depot glass work? It seems to be a bit reflective but what do I know. HD had some 4" square tubing and I made perfect cuts with my mitre saw so the main part of the prism is all set. I have some of the glass and was about to glue it but I want this to be my last one so I don't want to mess it up. Is HD glass ok or should I look at something else?

Thanks,
Craig Carrigan

Lifter · 13th January 2003, 08:23 PM

What kind of anamorphic lenses are you guys working on? Are they the kind that shrink the image vertically, or the kind that widens it?

tonypeps · 14th January 2003, 06:32 PM

Craig,

If you're ready for the final revision, check out www.framingsupply.com. It looks like the way to go for pre-cut, non-reflexive glass for a decent price. However, if you're like me, then your first attempt at gluing the glass pieces to the frame is going to result in a lot of smearing, smudging and leaks. So I'm using the cheapest picture frame glass I can find so I can practice my gluing technique.

Lifter,

Up until a few posts ago, we've been talking about lenses that compress the image vertically. But it looks like Michael F T has made one that expands it.

ccarrigan · 14th January 2003, 06:36 PM

I believe a couple posts back said not to use the framing supply place as the glass would blur the image, it was only meant for up close viewing. I have been practicing (two models down already) and want to do a final version now. The 4" square piping from HD really did the trick. You just have to have a 12" or greater mitre saw to go all the way through (my 10" wouldn't make it).

Craig

9th January 2003, 10:33 PM	#132
Jonathan M diyAudio Member Join Date: Nov 2002 Location: New Zealand	This is what I think would give a great picture... Anamorphic PAL DVD material is 720x576 in resolution. I think that an 800x600 panel, cropped to 720x576 would thus produce the exact pixels as are present on the DVD. Now, project that image through an anamorphic lens (One for 16:9, and one for 21:9 etc.) and you have a superb image. You can choose whether to compress vertically or expand horizontally as needed. No rescaling digitally taking place. Just optics. You also only need an 800x600 sized screen. Now, I am assuming that 2.35:1 DVDs are recorded anamorphically, so that the image takes up all the available vertical pixels. If this is incorrect, then at least it would work for 1.85:1 images. Obviously if you want to view a higher res image it'll start degrading quality, but for DVD's, I can't think of anything better. Just a thought

10th January 2003, 04:21 PM	#135
Michael F T diyAudio Member Join Date: Aug 2002 Location: NY NY	Expansion I like a bigger image and that's why I expand. The way I did it is just turn the prisms on their side. Instead of the point of the prisms putting vertically, they point to horizontally. It's literally turning the whole lens on it's side. I had a problem with air bubbles but since I didn't seal it up, I used a copper wire to pop them all. I also used Walgreens Mineral Oil and it looks great. Currently, I am using Plexi-glass and lose some of the brightness gains, but I still like it more since I don't have the black bars. BTW - to view a 2.35 movie with all of the pixels you need a scaler to zoom in on only the picture because the 2.35 DVDs have the black bars encoded on the dvd.

13th January 2003, 07:35 PM	#137
ccarrigan diyAudio Member Join Date: Oct 2002 Location: Hilton Head, SC	Glass? Where does everyone get your glass? Will Home Depot glass work? It seems to be a bit reflective but what do I know. HD had some 4" square tubing and I made perfect cuts with my mitre saw so the main part of the prism is all set. I have some of the glass and was about to glue it but I want this to be my last one so I don't want to mess it up. Is HD glass ok or should I look at something else? Thanks, Craig Carrigan

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9th January 2003, 10:22 PM	#131
JudeBarnes diyAudio Member Join Date: Oct 2002 Location: Portland, OR	I see so you send the projector full panel and then expand it to it's proper ratio, rahter than compress. I can see why this would be preferable in some isntances, for example, if the projector were much closer to the screen, and need to expand the picture larger ! But, I'm curious what you do to your source image exactly to get it squeezed without losing pixles? Do you turn the projector on it's side???

9th January 2003, 11:17 PM	#133
Axeman diyAudio Member Join Date: Jan 2002 Location: Nova Scotia Canada	I believe 2.35:1 movies are encoded anamorphically, but with the same ratio as regular widescreen movies. not all the vertical pixels get used, but more than if there was no optical compression in use.

10th January 2003, 01:24 AM	#134
Lifter diyAudio Member Join Date: Oct 2002 Location: California	Almost all DVD movies have anamorphic encoding on them. Some movies are 1.85:1, and some are 2.35:1. Movies that are 2.35:1 are actually filmed w/ an anamorphic lens to fit on 35mm film frames (which normally has a 1.85:1 aspect ratio). Then when projected, the theatre's projector will switch to an anamorphic lens to reverse the effect, thus making it wider. That's why 2.35:1 movies are refered to as "anamorphic widescreen". As far a DVD's go, anamorphic has a different meaning. Both 1.85:1 and 2.35:1 movies are anamorphicly encoded on most DVDs so that it will fit on a 16:9 (about 1.78:1). Usually, 1.85:1 movies have the sides croped just a slight amount, while 2.35:1 movies have black bars on the top and bottom (although they're of course not as big as they would be on a letterbox 3:4 picture).

10th January 2003, 04:51 PM	#136
JudeBarnes diyAudio Member Join Date: Oct 2002 Location: Portland, OR	Even though you say you lose some brightness overall I think you are gaining some brightness, too, by losing the black bars and filling it with pixels instead. I definitely CANNOT make my image bigger. If I do I will see the artifacts already inherent even more. The compression of the image has eliminated the two most pesky problems for HT viewing for my wife and I: 1. The black (grey) bars/lightspill 2. The horizontal scanline artifacts which occur on most LCDs with rapid vertically moving objects.

13th January 2003, 08:23 PM	#138
Lifter diyAudio Member Join Date: Oct 2002 Location: California	What kind of anamorphic lenses are you guys working on? Are they the kind that shrink the image vertically, or the kind that widens it?

14th January 2003, 06:32 PM	#139
tonypeps diyAudio Member Join Date: Sep 2002 Location: Naperville, IL	Craig, If you're ready for the final revision, check out www.framingsupply.com. It looks like the way to go for pre-cut, non-reflexive glass for a decent price. However, if you're like me, then your first attempt at gluing the glass pieces to the frame is going to result in a lot of smearing, smudging and leaks. So I'm using the cheapest picture frame glass I can find so I can practice my gluing technique. Lifter, Up until a few posts ago, we've been talking about lenses that compress the image vertically. But it looks like Michael F T has made one that expands it.

14th January 2003, 06:36 PM	#140
ccarrigan diyAudio Member Join Date: Oct 2002 Location: Hilton Head, SC	I believe a couple posts back said not to use the framing supply place as the glass would blur the image, it was only meant for up close viewing. I have been practicing (two models down already) and want to do a final version now. The 4" square piping from HD really did the trick. You just have to have a 12" or greater mitre saw to go all the way through (my 10" wouldn't make it). Craig

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