All About Aspect Ratio
Part 4 – What is an Anamorphic Projector Lens?
And do you really need it?
Both NEC and Optoma have anamorphic ready projectors. Optoma with the recently released HD81-LV Projector and NEC with the HT1000. As this is a fairly new term being thrown around, I am sure it has many people scratching there heads wondering just what exactly is an anamorphic lens? Is it a good feature to have? And what exactly does it do for me? As well NEC has the HT1000
An anamorphic lens is a lens that optically distorts the image this at first may sound like a bad idea, but as you will see it actually why it is a good idea. First some history, the anamorphic lens was first developed to allow filmmakers to capture a widescreen image onto a standard 35mm film. The Anamorphic CinemaScope process, is a lens that compresses the width of an image, squeezing the image during filming and then expanding or uncompressing it during projector playback to create a Widescreen effect. It is shot on a 35mm film with and aspect ratio of 1.33:1. The anamorphic lens produces a 2.35:1 aspect ratio when projected, and a screen size nearly two and a half times as wide as it is high. This is an increase of 75% from the standard 1.33:1 screen. The anamorphic prcess was perfected by Panavision, and in the 1970s became the standard 2.35:1 large screen format that is still in use today.
Above - is a 35mm frame from an old James Bond movie that was filmed in Anamorphic Panavision 2.35:1. If you look at the image you will find that the circle appears unnatural due to the anamorphic process which has compressed the width.
Above - When projected in the cinema through an anamorphic lens the screen size is nearly two and half times as wide as it is high. If the screen was 3m high the width would be 7.05m versus only 4m for the 1.33:1 aspect ratio.
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 HD81-LV Projector.
So how does it work? 4:3 native format to 16:9 widescreen.
As you might remember, the HT1000 is native XGA 1024×768, 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 but instead taken up by the black bars. Furthermore, since 25% of the lines are black bars, that means 25% of the lumen output is not being used as black is created by the projector by not passing any light.
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.
A 4:3 video projector and a 16:9 widescreen movie. The unused pixels result in black bars to the image top and bottom.
DVD movies are mastered by supporting the 16:9 anamorphic image. This means that 33% more vertical resolution can be got in use. Unfortunately now everything in the projected image is too tall and thin.
The only way to profit the extra resolution with the 4:3 video projector as well as use the complete brightness is to use an anamorphic lens and thus make an optical 1.33* vertical compress or squeeze to the image. The packed 33% resolution is taken in use, and the geometry in the image looks natural again.
There are two great benefits to this. First, the projector uses the full 100% of its native pixel matrix to display the image with no loss of resolution. So you get a higher resolution image, and pixelation is reduced compared to what you’d see with the normal 1024×576 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 1024×576 portion of the display.
16:9 native format to 2.35:1 widescreen.
As you might remember, the HD81-LV is native 1920×1080, which is 16:9 format. Normally when a 2.35:1 source is displayed on the HD81-LV it uses 817 lines instead of the full 1080 lines. Based upon the same concept above, the remaining lines consist of black bars above and below the image. So part of the resolution potential of the projector is not used but instead taken up by the black bars. Furthermore, since 25% of the lines are black bars, that mean 25% of the lumen output is not being used as black is created by the projector by not passing any light
You still get the black bars with the 16:9 projector, if the movie is wider than 16:9. In case of 2.35:1 movies there is still 33% vertical resolution unused.
In order to get these bars in use, you can stretch the image vertically so that every pixel in the 16:9 panel becomes active. This extra stretch can be done either with the HTPC or the external scaler. Also the latest projectors and some DVD players can do this stretch.
Anamorphic lens optically returns the original picture geometry, and thus this extra 33 % resolution is taken into the use. The resulting 2.35:1 ‘Cinemascope’ setup is also used in real movie theatres. When the picture gets wider it also gets larger, unlike in case of 4:3 and 16:9 setups.
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 1024×576 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 anamorphic lens being offered with the HD81-LV horizontally stretches the image into a 16:9 or 2.35:1 aspect ratio. With this type of lens the width of the resulting 16:9 image or 2.35:1 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 and 2.35:1 image.
One potential concern with anamorphic lenses
A potential problem to be aware of when considering the use of an anamorphic lens is this (for discusion we will assume your going from 4:3 to 16:9 : What do you do when you want to see regular native 4:3? When you put a lens that optically skews 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.
Wrap up
There is much to know and understand when it comes to anamorphic lens, so I must say please research and research. This has only been a quick rundown on a new feature that I am sure will become more popular and easier to use as new technologies come out.
I have not personally reviewed any of the anamorphic lenses on the market and can make no recommendations at this point in time. Nor can I state in certainty that they are right for everyone. If you plan on switch from format to format regularly I suggest you pay attention to your projectors mounting and check out all the different solutions that are available to you. Each lens maker does offer different mounting solutions and some will be easier to work with then others.