Anamorphic Lens Versus Zooming For Constant Height Screens

A popular thing in home theater today is to use a 2.35:1 aspect ratio screen instead of a 1.78:1 which is what HDTV is. The idea is to present scope movies wider than HDTV without black bars on the top and bottom to provide a more immersive experience for these films.

Two common ways to do this are to use either a lens or the projector zoom. When the projector is placed properly the lens zoom can be used to resize the image to fit a 2:35 screen to fill the screen to it’s height limit. The other option is to use an anamorphic lens along with special scaling. This system stretches the image to eliminate the black bars vertically and then optically stretches the image to fill the 2.35 screen with a 2.35 image.

Each system has advantages and disadvantages. Zooming is going to be less expensive, sharper, allows the image to be pixel mapped, will spill light around the screen from the black border and have higher ANSI contrast. An anamorphic lens will have smaller pixels, less wear on the projector lens mechanism, lower ANSI contrast, less sharpness, and additional lens distortion. The reduction in contrast and image distortion from the lens will depend on the lens and projector used. Anamorphic lenses require longer throw ratios as well that will typically lower the projector light output and likely offset any gains from being able to use the entire imager for 2:35 movies. Dark walls are a requirement for using a zoom lens to avoid seeing the light spill.

I recently aided a test with a Prismasonic H-FE1500R and a JVC DLA-RS35. The projector was mounted at a 2.0 throw ratio. Using lens zoom to fill a 10 ft wide 2.35 screen the ANSI contrast was measured at 250:1. With the anamorphic lens the ANSI contrast fell to 112:1. The light level from the screen only dropped 9 percent using lens zoom versus the lens with the same projector location. That difference in light output would be less if the projector would have been mounted at the minimum throw ratio. The light spill caused by zooming the 2.35 image was not visible on a dark brown wall. The image in this case was clearly better zoomed than not.

W. Jeff Meier

ISF and THX Certified Home Theater Consultant

14 Comments
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Garthzog

That ANSI figure is clearly a measure of the room, and not the lens (RS35 has been measured at over 300:1 ANSI so the room is already playing a part in your measures even before adding the lens). Did you measure the pj & lens without the room in the equation? You can do this in various ways, but one method I use is to black out the screen with black felt to eliminate any room reflections. Then you will get a result that is much closer to the pj and lens performance rather than what the room is doing. There’s a good chance the wider image was allowing more light to reflect back onto the screen from the side walls because the 2.35 image was closer to the walls than the 16:9 image was. I’ve measured quality lenses with an ANSI very close to the pj ANSI under controlled conditions.

W. Jeff Meier

I have also measured many quality lenses that do not affect ANSI much as well. This is the worst I have seen. I suspect it is the fact it is a prism and not just a lens.

You are not understanding the measurements. They are both on a 2:35 image and show the effect of this lens on the system. It also shows the light gain from the anamorphic lens approach is not very large when you consider the zoom effect on light output.

Garthzog

Sorry, missed that part – I assumed you’d made the same mistakes others have. In your case the measures are like for like, so comparable. I have to agree, they’re pretty poor results, even for a prism lens.

In some instances, I’ve seen zoomed projectors produce much the same light output as when unzoomed and using a lens on the same 2.35 screen. In those situations, the owner is using a lens for it’s other attributes rather than any light gain.

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