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Discussion Starter · #1 ·
I understand that when using a projector with an anamorphic lens that the projector stretches the picture vertically to fill the entire pixel grid and then the lens stretches it horizontally to make it look normal again.


Without using a lens what does an anamorphic dvd do? Does it just squeeze more lines in the same area? I saw in some website that using a 2.35 non-anamorphic dvd on a 16:9 screen leaves bars not only on the top and bottom but on the left and right until you zoom it on the dvd player. Is this true? My only display right now is a 4:3 tube hdtv.
 

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Not quite true. When using an anamorphic lens with a projector the image is stretched horizontally. Without the anamorphic lens, the full, native resolution of the image (if it's intended to be 16:9) will look squashed, ie. everything tall and thin.


CRT TVs consist of horizontal scan lines. Some TVs allow the scan lines to be compressed vertically so the black bars top and bottom contain no lost picture information. The less expensive TVs can only achieve the 16:9 ratio by using fewer scan lines, ie. the black bars contain wasted scan lines. Not good.


4:3 video projectors, like my Hitach SX-5500W, do not have scan lines but fixed, square pixels, therefore they can only 'unsqueeze' an anamorphic HD (1080i) transmission by throwing away picture information, like the cheaper TVs without adjustable scan lines. Not good.


The solution (in my situation) is an anamorphic lens attachment such as the $4000 ISCO lll. Ouch!


I should add that the same principle applies to a 2.35:1 image on a 16:9 projecter or TV. This extra wide format is regrettable in my view because there are no 2.35:1 displays (as far as I know) and therefore vertical resolution will always be compromised in relation to 4:3. Ie., unsqueezing a 16:9 transmission or DVD to produce 2.35:1 will always result in less vertical resolution than unsqueezing an anamorphic 4:3 image to give 16:9.
 

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There are two types of anamorphic lenses available. The panamorph lenses compress the picture vertically to make it less tall. This means that the image the projector is producing must be tall and thin, either through the scaling abilities of the projector or an external scaling of some type After compression the image will appear in the correct proportion. The ISCO type lenses expand a picture horizontally but again the image at the projector must be tall and thin to appear correct once the image is expanded from side to side.


EDIT: (Thanks MR. P.) Generally speaking the ISCO style compression works better with longer throw lenses while the Panamorph is okay with either long or short throw. The Panamorph site gives the following guidelines for PJ use and their lens.


1. Is the distance from your projector to screen (throw distance) between about 10 feet and 35 feet? If not, the image may loose sharpness.


2. Is your throw ratio (throw distance divided by screen width, same units) greater than 1.65? Less than 1.65 may cut off part of the image. Also, lower throw ratios create greater edge distortion.


3. Is the vertical dimension of the beam small enough to enter the Panamorph without getting cut off? The PSO series acceptable beam height is 1.5 inches maximum. The P752 goes up to 2 inches The P75J goes up to 3 inches.
 

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That's true, and the Panamorph is the cheaper way to go. It's a difficult decision because one is trying to get the benefit of extra brightness as well as extra resolution. Unavoidably, sticking anything in front of the projector's lens is going to reduce brightness and resolution to some degree, so one therefore has to weigh the cost, not to mention the trouble and stuffing around, against the over all net improvement.


Noticeable barrel distortion, softening of the image at the edges and corners, slight loss in resolution and brightness of the oringinal 'squeezed' 4:3 image, seem to me to be the unavoidable effects of the Panamorph and cheaper ISC0 lenses. That's why I would only contemplate getting the large aperture, razor sharp ISCO lll.
 

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Discussion Starter · #5 ·
Actually I was thinking of getting a 16:9 projector like the hs51 and then use the anamorph to make it 2.35. So it seems the panamorph might suit me better since I plan on using a 16:9 screen. The question is won't this increase resolution and light since your using the whole lcd area?
 

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ay221,

Since you have not yet got your projector, you can probably go either way. People who have already got their projecter and screen installed in a fixed position may not have as much latitude.


Having the equivalent of a black bar top and/or bottom of the screen from a 2.35:1 movie is a fact of life. It's unavoidable. If the projector is 16:9 and the screen is 16:9 (1.78:1), then any 2.35:1 source clearly cannot have the same vertical height.


The question is, by what process do you arrive at that situation. The native resolution of DVD is 720x480 (NTSC) or 720x576 (PAL) which doesn't match any of the common aspect ratios. To get the 16:9 ratio, the projector has to 'fill in' or extrapolate the extra pixels horizontally, so 720x480 becomes 853x480 or 1024x576 in the case of PAL. If your projector has 1280x720 pixels, the whole image is then scaled up to the full projector resolution.


Unfortunately (and I stand to be corrected here because there are many folks on this forum who know far more than I do on such matters, and as a matter of record I don't own a 16:9 projector, so I might have got it wrong), there are no displays that can stretch or interpolate the native 720x480 DVD resolution to 1128x480 to get the 2.35:1 aspect ratio. What they do is remove every 3rd or 4th pixel in the vertical dimension (or thereabouts) so the already extrapolated 853x480 (16:9) becomes 853x355 before scaling. That is, verticall resolution is unavoidably thrown away. Not good.


What the Panamorph does is compress the 480 pixels so that they occupy the same space, vertically, as the 355 uncompressed pixels. This ideally is a better solution than removing pixels. It results in greater vertical resolution but the same horizantal resolution and the full native resolution of the DVD format is preserved, as well as the full brightness of the projector (because all the projector's pixels are being used).


But nothing is perfect. The Panamorph is not perfectly transparent and therefore blocks a certain amount of light, so in practice the full brightness of the projector is not preserved. You get some level of brightness that's in between; some loss but also some improvement. I'm sure there are (or were) threads on this forum that have addressed this issue.


The same applies to resolution. The projector's lens is of a certain quality which probably varies with the cost of the projector. You possibly know from photography, you can stick a UV filter in front of a camera's lens and it doesn't seem to affect exposure or degrade the image. Theoretically it does to some very small extent, but it's so insignificant it's not worth mentioning or worrying about.


But this does not apply to sticking another lens in front of the camera lens. Anyone who uses teleconverters knows that they degrade the image, no matter how expensive they are. At the same time, they also magnify the image, so there are advantages and disadvantages which have to be weighed. Sometimes the disadvantages completely cancel the advantages and there's no net gain.


I would expect that both the Panamorph and the ISCO lenses will provide some net gain in terms of greater over all resolution and brightness, but in practice the net improvement will not be as great as it might appear to be on paper.
 

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There are some minor misconceptions here (or I'm not reading the question correctly).


If you plan on a 2.35:1 screen, the DVD player does nothing other than send the image to a scaler. Under normal circumstances (16:9 screen/16:9 native projector), the resultant image on the screen will be a 16:9 image. A portion of that image above and below the visible picture will be black. (Giving a 'letterbox' looking presentation.)


In our projector/scaler combination, the scaler takes the 2.35:1 image area and stretches vertically (by scaling, interpolation, etc). The image at this point would be 16:9 but everything would appear as tall and skinny. This image is then projected through an anamorphic lens which optically stretches the image to full width (restoring the geometry of the image). This provides a 2.35:1 full screen image.


Our screen is curved. At certain focal lengths, a slight pincushion effect can occur. Pincushion is not something that can normally be corrected in the set up parameters of a digital projector. The curve of the screen corrects the pincushion (plus rejects more ambient light and places more of the screen's reflected light into the viewing area).
 

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Some additional benefits of an anamorphic lens which have not been mentioned...


The lens does a wonderful job off masking any stray light from the front end of the projector, and of any light that may be creeping around the display chip shadow mask.


Also, even though they are very faint on my flat black paint screen masking, I can see the projected black bars above and below the main image coming from my HT1000. With a 16:9 format image, using the anamorphic lens eliminates these bars. However, they do come back with a projected 2:35:1 format image.


Lastly, if the anamorphic lens is bracket mounted and has some vertical tilt, I found there is a range of vertical image position adjustment that can be made by tilting the lens, without adverse effects to the projected image. This range of adjustment was much easier than trying to mechanically tilt the projector to adjust the projected image height. This came in handy because I have a variable size screen with movable masking. I zoom the projector to project onto the lkarger screen, and the image moves down as I zoom the image larger. Being able to tilt the anamorphic lens was a very easy way to realign the top of the image with the top of the screen.
 

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Quote:
Originally posted by Dennis Erskine


Our screen is curved. At certain focal lengths, a slight pincushion effect can occur. Pincushion is not something that can normally be corrected in the set up parameters of a digital projector. The curve of the screen corrects the pincushion (plus rejects more ambient light and places more of the screen's reflected light into the viewing area).
So does one take a normal screen and curve it somewhat, and if so how does one determine where to curve it? Or do you buy the screen pre-curved? Thanks.
 

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Quote:
Originally posted by Glenn Refling
Generally speaking the Panamorph style compression works better with longer throw lenses while the ISCO is okay with either long or short throw.
You are backwards there, Glenn. I have had both lenses with a short throw projector and the Panamorph handled it fine will the ISCO had some problems. The panamorph had a bigger aperature, so it could handle a larger image coming in, which is what a short throw projector would give.


For a long throw projector, I would prefer an ISCO, but really it boils down to: ISCO = Constant Height, Panamorph = Constant Width for any given zoom setting. You can get a panamorph to do constant height, but you must be zoomed out in one setting and zoomed in on the other.
 

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Dennis,


If the anamorphic lens is fixed, how do you handle 1080i 16:9 HD? The 1280 horizontal resolution is already borderline for many sources, even after considering the limitations from filtering etc. The only way to get 16:9 is to scale the horizontal down to about 975 which will definitely compromise most 1080i content.
 

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I've got a slight problem receiving 1080i broadcasts on my 1365x1024 projector, so I guess with a 1280x720 projector the problem would be the same or worse. I get more or less the full vertical resolution, but the 1920 horizontal resolution is obviously compressed, ie. the figures are tall and skinny. I'd assumed that this is how the signal is broadcast because I'd read that there were cheaper HD cameras being used that are only capable of 1440x1080i. In other words, I'd assumed that an anamorphic signal was being broadcast. However, a phone call to the broadcaster in question revealed that the broadcast signal actually is 1920x1080i (assuming the guy knew what he was talking about), so it seems my projector is throwing away horizontal resolution to fit the image on the 4:3 screen.


As I see it, I've got basically two options, (a) use an anamorphic lens to pull the image back into shape (or vertically compress the image in the case of the Panamorph) (b) set the HD receiver to 720P and the projector to 16:9 mode, in which case I get an image that's converted from 1920x1080i to 1280x720p.


I've considered getting an ISCO lens, but it doesn't seem worth it. If the broadcast signal was 1920x1080p, it probably would be worth it. The difference between 1080p and 720p is significant. The difference between 1080i and 720p is marginal. I'd get the benefit of a slightly brighter image, but in my opinion the very slight increase in vertical resolution (from the projector) would be completely offset by the slight over all loss in lens resolution from the ISCO or Panamorph.
 

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The motorized lens options in the 3-chip projectors will resolve this matter. Having said that, the projector/scaler combination we're using has not produced any softness or apparent reduction in resolution on screens upwards of 11.5 feet wide.


In the absence of a moving lens and a scaler integrated with this movement (ie, the changing of aspect ratios, lens movement and scaling should be transparent to the user); one is well advised to view the scaler, projector, and screen combination before making a purchase.
 

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Quote:
Originally posted by Dennis Erskine
Having said that, the projector/scaler combination we're using has not produced any softness or apparent reduction in resolution on screens upwards of 11.5 feet wide.

Dennis,

I'm not sure if you're referring to my claim that any lens attachment is going to degrade the image. Assuming you are, such degradation would not be noticeable (apart from obvious effects like pin-cushioning or barrel distortion) because there are two variables intertwined.


On the one hand, you have an undeniably greater brightness and resolution from the projector as a result of using the anamorphic lens, and on the other hand a lowering in brightness and resolution from introducing the additional lens into the system. As long as the former is greater than the latter, you would get no sense that the anamorphic lens is degrading the image.


Depending on the projector and the source, we have a best case scenario of 33% more brightness and 33% more resolution in the vertical dimension by using an anamorphic lens, or basically 33% more pixels. These figures are impressive, but don't apply in all situations. I don't see how an anamorphic lens could be of much use when viewing a 1920x1080i source on a 1280x720 projector. The aspect ratios are matched. The projector can do no better than 1280x720p so the quality of the image depends on the quality of the software/hardware (engine) that does the conversion from 1920x1080i to 1280x720p. An anamorphic lens would not serve any purpose in this situation (unless I'm missing something).
 

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Quote:
Originally posted by barryz
I don't see how an anamorphic lens could be of much use when viewing a 1920x1080i source on a 1280x720 projector. The aspect ratios are matched. The projector can do no better than 1280x720p so the quality of the image depends on the quality of the software/hardware (engine) that does the conversion from 1920x1080i to 1280x720p. An anamorphic lens would not serve any purpose in this situation (unless I'm missing something).
This set up is to optimize 2.35 or 2.40:1 DVD material.
 

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Quote:
Originally posted by Jim Noyd
This set up is to optimize 2.35 or 2.40:1 DVD material.
Sorry! I'm still not with you. Optimise 2.35 on what projector? If the resolution of the projector can accommodate both the native resolution of the DVD format and any 'extrapolated' resolution that's required to rescale to the proper aspect ratio, then an anamorphic lens is serving only half its purpose, ie. enabling more brightness from the projector.


I might have got things wrong here, but as I understand it a 2.35 DVD source on a 1280x720 projector will be scaled up from its native resolution of 720x480 to 1280x720, which is the wrong aspect ratio. To bring it back to the correct AR, the projector has to scale down the vertical resolution from 720 to about 545 pixels which is still higher than the original encoded resolution of 480. However, the image is then not as bright because of the black bars, top and bottom. There's a theoretical loss of about 25% in over all brightness.


Introduce a Panamorph or ISCO, you restore that extra brightness, less the brightness lost by the additional lens (which brings it back down to, say 15% extra brightness) less an over all loss in resolution, and you have a net improvement which hardly seems worth the effort and expense.


I accept that the unavoidable loss in resolution that any additional lens is going to produce could be offset by using add-on scalers that are more sophisticated and state-of-art than the projector's in-built scaler. But that involves even more expense. I would seriously question whether such expense is justified in that situation.
 

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Quote:
Originally posted by barryz
Introduce a Panamorph or ISCO, you restore that extra brightness, less the brightness lost by the additional lens (which brings it back down to, say 15% extra brightness) less an over all loss in resolution, and you have a net improvement which hardly seems worth the effort and expense.


I accept that the unavoidable loss in resolution that any additional lens is going to produce could be offset by using add-on scalers that are more sophisticated and state-of-art than the projector's in-built scaler. But that involves even more expense. I would seriously question whether such expense is justified in that situation.
That is the thinking behind the "Fixed Height" solution. You will have to make your own judgement if it is worth the expense of the additional lens, scalar and curved screen for better 2.35:1 DVD playback.
 
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