The Anamorphic Lens – An Introduction

Panamorph UH380 and ATH2 Motorized Sled

Anamorphic

Is defined as: Denoting or relating to a distorted projection or drawing that appears normal when viewed from a particular point or with a suitable mirror or lens.

The burning questions about the projector anamorphic lens are; what are they for, do I need one and will it improve my image?

A Little Image Background

It all started with that first pin-hole camera back in about 300BC, the camera obscura and by 1685 the first practical camera was invented by the French inventor Joseph Nicéphore Niépce. Since that early time photography has developed in leaps and bounds from stills to movies and all the way up to our modern-day iPhones. All these devices create pictures with two things in common, they all have a width and a height. The ratio of a pictures width to its height is known as the images aspect ratio and is a dimensionless number. So if an image had an aspect ratio of 2:1 it would be twice as wide as it is high. It could be 2″ wide and 1″ high or 2 feet wide and 1 foot high, the dimensions do not matter only that they are measured in the same units.

Many image aspect ratios have been used by displays, photographic devices and movie cameras from an iPhones 6:13 all the way up to 4:1 Polyvision and Disney’s Circle-Vision of 12:1.

Do not confuse the image or display aspect ratio with the pixel aspect ratio. For electronically created images pixels are the smallest element of an image and are what the image is composed of. It does not apply to photochemical film except when scanned to an electronic file. CRT displays do not have individual pixels and their effective pixel size is the diameter of the scanning electron beam. Pixels maybe either square (1:1), now most common, or rectangular, most common for standard definition TV’s. (The impact of pixel ratios, that are not square, on aspect ratio shall not be reviewed here.)

The image aspect ratios most of us are familiar with in the consumer TV/movie worlds are: 1.33:1 (4×3), 1.77:1 (16×9), 1.85:1, 2.35:1, 2.39:1 and 2.40:1. With SD TV’s starting at 1.33:1 and now moving to HD/4K/8K 1.77:1 (16×9) and most current DVD/Blu-ray movies being either widescreen 1.77:1 (16×9) or cinemascope 2.39:1 or 2.40:1.

So now we know what a picture or image aspect ratio is and what common ones are in use. Clearly we can see that fitting a cinemascope image of 2.40:1 on a widescreen 1.77:1 screen or vice versa is going to create technical issues for the display/projector system.

NOTE: An anamorphic lens is sometimes used with still and movie cameras in order to pre-distort an image so that it will fit within a particular frame size of photochemical film or digital image sensor.

Most movies are encoded to DVD plastic discs as linear scans that fit within a 16:9 native window. Some are encoded as pan and scan that follows the action and expands the movie to fully fit the 16:9 window while others use the full height of the 16:9 window and are electronically compressed horizontally to fit into that 16:9 window, assuming that they will be electronically stretched back to their correct aspect ratio by the player or displaying device. We are assuming the first linear approach, in that the majority of movies are encoded to fit into the width of a native 16:9 screen for display. (I am ignoring the issues associated with some modern movies that use mixed aspect ratio content that switches between 2.39/2.40:1, 1.77:1 and IMAX.)

Fitting The Image

Virtually all modern consumer TV displays and projectors now use a native image aspect ratio of 1.77:1 (16×9). The panel display technology; LCD, LED etc. for the TV’s and projectors are built to support this ratio in order to conform to the electronic scanning standards and square pixel counts adopted by SMPTE and the ITU. Fitting a different image aspect ratio to a native displays aspect ratio of 16×9 is quite easy these days. Modern image scaling engines can crop, expand and scale images to fit within the standard 16×9 display area without producing too many objectionable artifacts. However, scaling is not without some visual impacts.

Display and projector scalers simply inserts black bars to each side (pillarboxing) of a 1.33:1 (4:3) image and the top and bottom (letterboxing) of a 2.40:1 image in order to fill the entire 16×9 screen area. Some displays also have other scaling options to give the viewer different views of part of the image or handle other non-native aspect ratios. The issues with black bars are that they:

1. Reduce the effective diagonal size of the display by only using part of it.
2. Reduce the available brightness due to the blacked out areas.
3. Reduce the perceived vertical image resolution of a 2.40:1 image by only using 74% of the displays horizontal pixel lines

For 2.40:1 cinemascope movies the approximate reductions are as follows:

1. The diagonal size of the display is reduced by approx. 6%
2. The available brightness is reduced by approx. 26%
3. The vertical screens resolution is reduced by approx. 26%. This equates to:
   1. HD: 280 lines or 537,600 pixels
   2. 4K: 560 lines or 2,150,400 pixels
   3. 8K: 1120 lines or 8,601,600 pixels

Clearly for a flat panel TV display we are stuck with these issues and remember that turning up the displays brightness may affect black levels! However, for projectors things are different and they need to be.

Brightness And Light Sources

A projectors light source is very different to a flat panel display. It is effectively a single point of light that has to be ‘spread’ over the projection screen using a series of lenses. Flat panel illumination is provided by numerous light sources spread across the edges and/or rear of the panel (excludes LED panels as each LED is a light source). This difference allows flat panels to create quite high brightness levels. Projectors however are limited to what light can be obtained from just one bulb or at best three and sometimes four combined LED light sources. HDR by its nature requires very high peak white levels which are only occasionally used by the programming. Creating such intensely bright light sources for occasional use from one bulb or several LED panels is not cost effective in a projector and even if it was possible would create huge levels of heat that needs to be removed by fans that tend to be noisy.

So while the above brightness issues for a flat panel TV can be in some way be mitigated by clever lighting topologies, it is a different story for a projector that cannot cost effectively get close to the required brightness to meet HDR requirements. Loosing any brightness for the display of a 4K UHD projector image therefore significantly impacts what you see.

So we need all of the projectors panel area to be passing light for as many aspect ratios as possible and not having part of it electronically blanked off for none native aspect ratios. This is where the anamorphic lens comes to the projectors rescue fixing BOTH its light loss and improving the resolution for cinemascope movies.

So if we want to fill your screen with a cinemascope image then you need a cinemascope screen. There are arguments as to exactly what its aspect ratio should be, 2.35:1 or 2.40:1 but for now I have assumed that it is 2.40:1. Also I have assumed that you have a fixed projector location.

Projector Lens Zooming

Clearly and by far the most common and least expensive way of fitting a letterboxed cinemascope image to a cinemascope screen is by zooming out the projectors lens. This technique has one advantage in that the images brightness will increase as more light will be released from the projector. Depending upon your particular circumstances by as much as 20%. You should note that in an ideal world that this almost compensates for the effects of the letterboxing. However, you can do nothing to compensate for the lost pixels, most will not get anywhere near a 20% brightness improvement and for 4K UHD the use of high power is generally mandatory in order to get closer to the required specular highlight and general brightness levels. So while zooming is a ‘quick fix’ to fitting the image to your cinemascope screen you are not getting the best possible image performance.

The Anamorphic Lens

These pieces of highly engineered precision glass, in conjunction with the projectors or players scaling engine, are designed to expand or compress the projectors light beam in such a way as to enable the full panel image to correctly fill the entire 2.40:1 aspect ratio of a cinemascope screen. This lens is positioned directly in front of the projectors lens light path and optically distorts it in one of two ways:

1. Horizontal image stretch
2. Vertical image compression

Typical Panamorph Paladin DCR lens placement, using vertical compression.

Image Credit: Panamorph – DCR Lens

Horizontal stretching optically expands the image to fit the cinemascope screens width and the projector or players scaling engine stretches the image vertically filling the 16:9 projector panels full height thereby restoring the correct 2.40:1 image aspect ratio and increasing brightness and resolution. These lenses typically create up to a 30% increase in brightness over the original letterboxed 16:9 screen display.

Vertical compression lets the projector scale the movie to fill its 16:9 panel, stretching it vertically and thereby increasing brightness and resolution. The lens then optically compresses the image vertically to the correct aspect ratio to fit the 2.40:1 cinemascope screen. These lenses are claimed to create up to a 38% increase in brightness over the original letterboxed 16:9 screen display.

If you wish to project a 16:9 or 4:3 image onto a cinemascope screen you may:

1. Remove the lens from the light path – maybe be achieved manually or using a motorized sled (4:3 still needs to be electronically scaled)
2. Leave it in the light path and instruct the projector or players scaling engine to under scan the projector panels to create the appropriate aspect ratio image

In both cases you should ideally bring down side screen black masking panels to restrict the screen width to the required aspect ratio. This helps with the perceived contrast ratio. If you leave the lens in the light path there maybe some loss in resolution as the image is probably no longer pixel mapped to the projectors panels, with any losses in brightness due to under scanning the projectors panels being made up for by opening the projectors iris and/or running in a higher power mode.

Many modern projectors and players have various scaling options for displaying other aspect ratios, thereby allowing the lens to remain in the light path as shown in the above image.

Examples of some modern day anamorphic lenses:

Image Credit: Panamorph – Paladin Lens

Image Credit: Panamorph – UH480 Lens

Image Credit: Prismasonic Lens

Image Credit: TECHHT – ISCO Lens

Anamorphic Lens Issues

All is not roses in the anamorphic lens garden and its use does have some side effects. However, overall these issues are more than compensated for by the improvement in the brighter, better resolved and improved larger image involvement.

1. Cost – high especially if an automated sled is used
2. Loss of light – generally minimal being a few % with modern glass and coatings
3. Loss of resolution – generally minimal with modern glass techniques and coatings
4. Barrel distortion – generally minimal at the correct throw distance and is removed by over scanning to the screens black borders
5. There is a minimum throw ratio requirement – this ratio is the screen to projector distance divided by the 2.40:1 screen width. At least 1.4:1 or 1.6:1 or greater
6. Color fringing – generally minimal with high quality lenses and coatings. Can be mitigated by the use of projectors pixel alignment
7. Subtitle placement – black bar placement is sometimes assumed by the films producers. Can be moved to in-picture by some players
8. Image scaling must be available from the player or projector – most modern projectors and many players support this
9. May want screen side masking panels to improve the perceived contrast ratio for other aspect ratios

High quality lenses generally suffer very little from any of the above issues. I still use my Panamorph UH380 anamorphic lens with my pseudo 4K JVC DLA-RS640 projector and almost all modern projectors and players come with suitable scaling options with some players, like the Oppo 203 & 205, also being able to move subtitles.

Anamorphic Lens Manufacturers

Here are the top of the line anamorphic lens manufacturers:

• Panamorph
• Schneider/ISCO
• Prismasonic
• Optoma
• Epson

Remember that when projecting native 4K and especially 8K images any minute imperfections in the design of the glass systems and its coatings will seriously impact your available resolution, create color fringing and drop brightness. Cheap is not the way to go when buying these lens’s if you want them to create a stunning image.

For more information on flat panel display and projector operation read this two part post.