What is an anamorphic lens?

Evan Powell, September 18, 2003

NEC has recently been running a special promotion on the HT1000 that has, as one of its options, the inclusion of an anamorphic lens with the purchase. This has led many folks to wonder.... what is an anamorphic lens? Is it a good thing to have? What does it do?

Basically, an anamorphic lens is a lens that optically distorts the image. That sounds like a bad thing, but we will get to why it is good in a minute. First, some history. The anamorphic lens was first developed in the film industry when they wanted to use standard 35mm film to record images in widescreen format. The way they did it was to fit the film camera with a widescreen format lens that optically compressed the image so that it would fit into a 35mm film frame. Then when the film was played through a projection system, the projector was fitted with another lens that reversed the distortion. In that way the compressed image that was recorded on the 35mm film was projected onto the screen in natural, uncompressed widescreen format.

This anamorphic lens technology has been adopted by the projector industry and is available to you if you want to use it. The most common application is to use the anamorphic lens to convert full 4:3 native format into 16:9 widescreen format, which is what is being done on the HT1000. How does it work?

As you may recall, the HT1000 is native XGA 1024x768, which is 4:3 format. Normally when a 16:9 source is displayed on the HT1000 it uses 576 lines instead of the full 768 lines. The remaining lines consist of black bars above and below the image. So part of the resolution potential of the projector is not used. Furthermore, since 25% of the lines are black bars, that means 25% of the lumen output is not being used.

However, most 4:3 projectors like the HT1000 have the ability to horizontally compress a 16:9 source into their full 768 line pixel matrix. If this were displayed with the normal lens, the image would fill a full 4:3 format screen, but it would look vertically stretched…people would look excessively tall and skinny. By affixing an anamorphic lens to the projector in front of its normal lens, the image is optically undistorted as it passes through the anamorphic lens, so it comes out looking like a natural widescreen 16:9 image.

There are two benefits to this. First, the projector uses the full 100% of its native pixel matrix to display the image. So you get a higher resolution image, and pixelation is reduced compared to what you'd see with the normal 1024x576 image. Second, since you use the full pixel matrix, you get the full lumen output of the projector—the picture is brighter than it would be if using just the 1024x576 portion of the display.

Two types of anamorphic lenses

Without wanting to complicate this much further, it needs to be pointed out that there are two types of anamorphic lenses on the market. One compresses the image vertically, and the other expands the image horizontally. Ultimately they accomplish the same thing.

The lens being offered with the HT1000 compresses the 4:3 image vertically. That means at any given throw distance, the width of the resulting 16:9 image with the anamorphic lens will be the same as the width of the native 4:3 image (or 16:9 image in 1024x576 format) that would otherwise be displayed without the lens. What you get is a brighter, higher resolution 16:9 image, and the lens does not change the projector's throw distance.

The other style of anamorphic lens will take a 4:3 image and optically stretch it horizontally into a 16:9 image. With this type of lens the width of the resulting 16:9 image is 1/3 wider than the 4:3 image that would otherwise be projected from that distance. Therefore, this type of lens shortens the throw distance of the projector for any given size of 16:9 image.

One notable problem with anamorphic lenses

A potential problem to be aware of when considering the use of an anamorphic lens is this: What do you do when you want to see regular 4:3 material? When you put a lens that optically distorts what is being projected in front of your projector, it distorts everything, whether it is pre-compressed 16:9 or not. So when you try to play native 4:3 material through it, you get an image that is distorted horizontally--people are shorter and fatter than normal.

If you don't plan to watch any 4:3 material, or if you don't care if your 4:3 image is distorted, this is not a problem. However, if you want to see your 4:3 sources in normal aspect ratio, you only have two choices. The first is to physically remove the anamorphic lens when switching to 4:3 material. The second is to use an external scaler that can pre-squeeze the 4:3 signal so that it comes out normal when passing through the anamorphic lens. Neither of these is an overly appealing solution for most users.

The lens offered by NEC attaches to the projector via a hinge and can easily be swung down out of the way when you don't want to use it. But if the unit is ceiling mounted, this may still be a nuisance—think in terms of having a small stepladder standing by when you want to switch from 16:9 to 4:3 viewing.

Conclusion

There are those who swear by anamorphic lenses because of the higher 16:9 resolution and brightness they can get from a native 4:3 projector. They can be used with not only the HT1000, but any 4:3 format projector that can horizontally squeeze a 16:9 source into its full 4:3 display. At the recent CEDIA show, JVC was demonstrating their DLA-SX21 with an anamorphic lens, and the image was gorgeous. From this demonstration alone it was easy to see why videophiles have embraced them.

We have not reviewed the anamorphic lenses on the market and can make no recommendation on one over another at this point in time. Nor can we state categorically that they are right for everyone with a 4:3 projector. Certainly if you plan to switch frequently between 16:9 and 4:3 sources we suggest that you keep the logistical issues of mounting and removing the lens uppermost in your mind as you check out the alternatives available to you. Each lens maker has different mounting solutions, and some are easier to work with than others.

For more information you can visit the websites of companies that manufacture and market anamorphic lenses. Panamorph makes a lens that compresses the 4:3 image vertically. ISCO Optics makes one that expands the image horizontally. We suggest you consult with Audio Visual dealers for more details, options, and pricing.

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