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Discussion Starter · #1 ·
I did a search on ebay and found a few anamorphic 35mm lenses for sale. These lenses do a 1:2 expansion in the horizontal direction. These lenses are also cheap - less than $100.


I have a 4x3 projector - an LT150. A doubling of the horizontal dimensions would give me 8x3 which is 16x6.

Normally, my projector, in Cinema mode, scales the image to 1024x576. Now, let's say I tell my projector not to do any aspect ratio control. That results in my screen being 1/3 taller.


1.33 * 6 = 8 giving me a 16x8 screen. Which is pretty darn close to 16x9.


Now, the major problem I see is that the first lens I found on ebay could only focus to 50 feet. I'm assuming that's the shortest, not the longest distance. But if a lens could be found that could go lower...


Crazy?




[This message has been edited by rickforrest (edited 08-15-2001).]
 

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Huh?


4x3 is four units WIDE to three units TALL. Your equation fell apart right away.


If oriented as specified, this lens would give you a 4x6 ratio image...an aspect of 0.66, a far cry from 1.78 (16:9) and even a far cry from your original (better) 1.33.


Can the lens be turned the other way?
 

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Well, I got a headache trying to figure out your math. I can't follow how a 2X expansion would work when what we need is 1.33X for 16:9 DVD


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Greg
 

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Quote:
If oriented as specified, this lens would give you a 4x6 ratio image...an aspect of 0.66, a far cry from 1.78 (16:9) and even a far cry from your original (better) 1.33.
Actually, a 2X lens will give 8:3 which is 2.67:1. Too much expansion.


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Greg
 

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Discussion Starter · #6 ·
Quote:
Originally posted by milori:
Huh?


4x3 is four units WIDE to three units TALL. Your equation fell apart right away.
Then I must really be stupid because I knew that 4x3 was 4 wide by 3 tall - and I still think I've done the math correctly. Let's do it again.


4x3 no lens

8x3 with the lens, which expands 1:2 in the horizontal direction.

8x3=16x6 elementary school math


Screen is 6 units high. Turn off squeeze that an LT150 or VT540 does in Cinema mode. Picture is now 33% taller = 8 units high.


16x8.




[This message has been edited by rickforrest (edited 08-15-2001).]
 

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Discussion Starter · #7 ·
Quote:
Originally posted by Mad Chemist:
Actually, a 2X lens will give 8:3 which is 2.67:1. Too much expansion.

COuld you guys please read my post again? I turn off the squeeze that my pj does, which expands the 3 to 4. which makes it 16x8.


Let me restate. The vt540 and the LT150 are 1024x768 projectors. When fed a progressive component signal, you can put it in Cinema mode, which scales the picture out to 1024x576. If you take it out of cinema mode, the picture will be 1.3333x576 tall.
 

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Discussion Starter · #8 ·
Quote:
Originally posted by Mad Chemist:
Actually, a 2X lens will give 8:3 which is 2.67:1. Too much expansion.



The "too much expansion" is countered by turning off the cinema mode of the lt150/vt540, which vertically expands the image, and results in tall skinny people. The anamorphic lens expands these tall skinny people to be just slightly too fat (16x8 instead of the desired 16x9)





[This message has been edited by rickforrest (edited 08-15-2001).]
 

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I'm shaky on this but what the heck:


Out of a DVD player comes a 4X3 skinny image which has to be either stretched to 16X9 or squeezed to 16X9. I think the cinema mode does a squeeze.


1.Now, take that 4X3 (full screen) skinny image and use the 1:2 "stretcher" lens. Result: the image will be too wide (8X3, fat people?), note, there is no pj squeeze to turn off, since you are already using the whole screen.


2. If the pj cinema mode (squeeze) is on, you already have the 16X9 and using the lens in that mode will really distort the image, but if you turn off the cinema mode, then you are back to case 1 above.


So, how far off am I?



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Jim Story

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I read horizontal as vertical. I humbly withdraw the "huh?".
 

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And replace it with a DOH ??? http://www.avsforum.com/ubb/biggrin.gif


Apart from the maths though many people have looked at these 35mm anamorphic lens's and the same problems keep coming up...
  • Long focal lengths
  • Small aperture for light beam
  • Light eating lens's


All in all it makes them a difficult proposition... Has been done a few times with Panatars (ultra and super) but not what you would get from ISCO or Pannie...


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Discussion Starter · #12 ·
Phreddy -


Of your three objections


1. focal length - this is a problem, I know.

2. small aperture - maybe not a problem on the lt150? this lens is tiny.

3. loss of brightness - but you're using 33% more of the lcd panel, and thus getting 33% more light out of your pj (i hope). if that assumption is correct, then if the anamorphic lens eats less than 33% of the light, you're ahead of the game, no? You'd also get the advantage of a shorter throw, if that's helpful. Which it would be for me because it gets my pj in front of a troublesome ceiling fan, that cannot (or rather, I'm not allowed) be moved.


So, if I'm just dying to try this, the only real problem I think) is number 1 - focal length. Are there any of these cheap used lenses out there that have a very short focal length, i.e. 6 feet?


[This message has been edited by rickforrest (edited 08-16-2001).]
 

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Now I guess it is my turn at a little math http://www.avsforum.com/ubb/smile.gif You have a native 4x3 projector (1024x768). With the lens you will still have 1024x768 available pixels, BUT they will physically produce an image that has an 8:3 aspect ratio. Now assuming you want to display a 16x9 image using a scalar that can give you what you want, you would want the 16x9 image to take up a 5.333x3 portion of the 8x3 image. Thus you would use a pixel grid of 683x768 (or 524544 total pixels). If we would have displayed the 16x9 using the native panel without lens it would have used 1024x576 pixels (or a total of 589824 pixels).


Unfortunately the image would be dimmer (neglecting light loss by lens) by the ratio of 524544/589824 = 0.89 (11%).


The lens would not help out 16x9 stuff except maybe the fact that the pixels are not square but have a 2:1 aspect ratio.


The lens would help out for display of 2.35:1 material. With the lens you would use 902x768 pixels (692736 total pixels). Without the lens you would utilize 1024x436 pixels (446464 total pixels). Thus the image would be brighter by the ratio of 692736/446464 = 1.55. 55% brighter!





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STOP DVI/HDCP!

DVI/HDCP! ~= HD-DIVX!!!

DO NOT SUPPORT JVC or anyone else who supports this!
 
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