Tel: 905–690–4709 dk@tfwm.com - Darryl Kirkland, Publisher

Optical Filters for HD and HDV

Improving your workflow and craft with optical filters

Hollywood uses filters on nearly every one of their small screen (television) and big screen (movies) productions. They know that using optical filters will make their entire workflow easier and more cost efficient. As you learn to be proficient with optical filters you will find that they are what can help distinguish you from the competition and give a greater sense of craft to your work.

Here is a little insider’s view of some of the issues changing from SD to HD created on the set of a very popular and very successful Hollywood television production changing from SD to HD as told to me by an associate:

I arrived at Culver Studios and entered the sound stage.

I met John, the DP (Director of Photography) and he introduced me to the entire camera crew complete with camera operators, assistants, utility people, Key Grip and Gaffer and even the head make-up artist for the show. These are all the usual suspects in a TV production. But on this shoot there is another position, new for me. I was introduced to Ken, the DIT….

Now at first you might think the crew is using some nickname for this guy that, well frankly, sounds a bit derogatory. He is the DIT what? Actually DIT stands for Digital Interface Technician. He is responsible for making sure the signal that is coming out of the Sony Cine Alta Digital Cameras (there will be four of these on the series, at about $250,000 a camera package) is within the correct parameters. As it turns out, Ken is totally familiar with the entire operation of the cameras, as well as, all the signal distribution infrastructure and recording equipment. Ken is an excellent teacher for all the crew and really understands how to translate all this technology into a real efficient workflow that will serve everyone’s artistic needs as well.

When John starts the discussion with the team about facial image enhancement for HD, Ken is one of the best enthusiasts. (Apparently this is rather unusual for a DIT as most just want to go by what the wave form monitor Generator “Scope” depicts and have very little image capture know how or acceptance.)

We start to do the first image capture using some of the stars’ stand-ins right on the set using the exact same lighting setups as the established set called for. The actors get on their marks and the make- up artist does some quick touch ups. Then John calls me over to the “BLACK TENT”. In this 6’ x 6’ POP-UP Canopy tent, they have positioned a Sony HD CRT Broadcast Calibrated Monitor and all the data recoding hardware on carts.

As the camera rolls we see the live and startling sharp image on the screen. John calls for various diffusers to be inserted into the Matte Box and we do a series of A and B comparisons, without filters, with filters and so on. He starts with his old favorites but he is disappointed by their performance. They are too manipulative on the desired image. The old style filters are actually introducing aspects he has to reject; such an extreme blooming in the neon lights in the background, flares and other changes in contrast that will completely change the look of the show. They are all what John calls, “TOO INTRUSIVE”.

Then Ken motions for John and me to look at this other small monitor that is located over on the side of the Evertz convergence equipment. This is a Standard Definition monitor. Ken wants John to look at the image to be sure to “guard” for the standard definition image as well. This is very important as the series will be simulcast in both formats HD and SD. Here is just another reason why conventional, old, motion picture diffusion technology can let you down. Since the number of lines in SD is roughly only 480, the effect of your diffusion can actually appear twice as strong as HD. Sure enough, using the old style diffusions resulted in a much stronger effect on the SD monitor. Filter effects just starting to appear in the HD image were blowing out the SD image. So again John gets rather frustrated. The images were softened too far in HD and even went from worse to unusable in the SD rendering on the screen.

Then John tries the HD Soft starting with the Number one, two and three. He really likes what he sees. The filters are doing away with the unwanted facial defects while not changing the overall image quality of the scene. Even the image on the SD monitor is great! John looks over at Ken who gives him a big double thumbs-up from in front of the waveform monitor- it’s working!

The argument of “fix it in post” or “can’t we do that with in-camera settings” are valid, to a point. However, there are many reasons why “fixing it in post” is not the best way to go and incorporating optical filters into your HD workflow, no matter what type of shooting you do, is going to take you to a new level of shooting.

Here are a few reasons for using your filters rather than waiting for post:
Lens Protection – Protect your lens from scratches and moisture. Most rental houses will not allow a camera to leave their facility without a protective clear filter on the lens. With the improved resolution of the new HD and HDV cameras, there is more wiping and cleaning of the lens then ever before. Eliminate the possibility of damaging your lens with an optically correct, protective, clear filter.

Filters can save time and frustration in post-production. The work quality of post-production houses is varied from facility to facility, as is a facilities ability to work with different types of productions. An over reliance on post-production takes the artistic control away from you and transfers it to them. Even if you do your own editing the use of optical filters will provide more time for the actual editing process and the story telling rather than spending all your time on making corrections or creating effects.

Not waiting to see the effect you want in post eliminates uncertainty by allowing you to see the effect you want immediately. You can then accept the effect or change the filter to achieve another effect. You will now be using the immediacy of video to your artistic advantage rather than waiting to correct the inefficiencies and inadequacies of HD in post. You can check lighting, composition, focus, and any filter effect at the time of the shoot with all the elements present to correct it.

As opposed to in-camera effects and adjustments, the effect of various filters can be easily seen, thus removing the need to go through multiple menus to change camera settings.

Your talent (and producers) can see the softening or warming effect on the monitor before, during, and while the scene or segment is shot or played back. The “intimidation factor” of talent reviewing their HD image right in front of them is well documented. Whether it be an interviewee, a bride, a preacher or just your family video; optical filters help relieve the anxiety of HD.

Filters can be viewed in combinations with other filters, the combined effect being visible on a monitor. The interaction of multiple filters is difficult to duplicate with software.

You can bring the optical correction to a known standard, leaving more latitude for digital effects. Detail critical for effective grading and compositing operations cannot be restored later if not sampled or digitized in the first place.

Of course, consider budget. Filters save money and worry. You can create what you want the shot to look like already in your chosen method of storage, eliminating the need to create it in post. This ensures that you will not have to compromise your production due to money and time limitations created by going over budget.

Still not convinced that optical filters are worth your time? Here is another tale of how the simple use of filters overcame a problem that, at the time seemed insurmountable.

First thing one Monday morning I was called by a dealer who had a big problem. They had just installed a new 3-camera HD set-up for a church and the results were not acceptable to the father of the preacher. The initial shots of him on the screen in the overflow room were bad enough, but the DVD of the first recorded service was “scary.” The issue was simple: they did not have the budget or the space to light the pulpit as you would an HD studio and the results were pure HD. It showed every pore and every line, the depth of field was off and the three camera’s skin tones did not match. Lighting changes and in-camera adjustments helped with some of the issues but could not create an acceptable image. Long story made short: a diffusion filter with a slight warming effect on all three cameras allowed the church to keep its pulpit looking like one; not (a) looking like a TV studio, allowed real time DVD recording with pleasing skin tones and facial images AND saved time in post production for the more intensive task of DVD authoring.

Now that you are convinced that it is worthwhile for you to learn about and use optical filters, what’s next?

Learn a bit about filters through sources such as the American Society of Cinematographer’s (ASC) website and books, the many books on filters and digital cameras, on-line user groups, organizations like MCAI and other Videographer’s Associations and best of all: your own experimentation.
As you start to experiment and use filters here a few pointers:

The contrast ratio of today’s digital cameras is less than that of film. The color response is different. Older generation filters may not be suitable for use with today’s DV, HD, and HDV cameras. Try not to use those made of soda lime glass, as it tends to impart a subtle green tint. This was not such an issue for film and even for some SD cameras, but can be an issue for the new digital cameras due to possible inaccurate color sampling and loss of color saturation. Modern filters designed for HDV and HD applications utilize a water white or Schott B270 Crown Optical Glass that does not contribute to sampling inaccuracies.

Manufacturers are beginning to understand the need for filters used in HD to have a higher standard of flatness then those of the past. Older filters that are not as flat may produce distortions in today’s cameras that become especially evident during slow pan and tilt movements. Laminated filters, especially color graduated filters should also be avoided as they can produce small focus shifts and can also create a banding pattern that may lead to pixilation.

No matter what filters you choose be selective and use them tastefully. Use glass filters, as plastic can distort the image especially on long focal lengths. Choose low densities to begin with such as 1/8, 1/4, 1/2 or at most a 1. Many companies are now deciding to scrap the 1/8 to 5 density valuations for simple 1, 2, 3 density values for filters made specifically for HD.
Buy a sunshade or matte box. This will help to keep flares off your lens, hold your filters, and make you look more professional.

Whether you choose to buy a matte box or decide to use simple screw-on filters start with a polarizer and neutral density (ND) filters. To obtain the required reduction in file size, today’s cameras cut out what they consider irrelevant details. In almost all cameras they have tended to look into the shadows for information that can be “lost” resulting in a potentially significant loss of shadow detail. Polarizing filters increase contrast and improve your shadow detail by reducing light scattering.

Another use of the polarizing filter is to control the reflection that light creates in windows, water, and glass lenses. Since light bounces around in all directions along its axis these surfaces often create an increased scattering of light. The object is not to eliminate all of the reflection but to reduce it to a point where the camera can achieve the effect without overwhelming the scene with scattered light.

Polarizing filters may also be used for reducing the effect of haze or as an ND filter.

Shooting with a wide aperture is always a good idea. ND filters and ND graduated filters are used to control the quantity of light that enters your camera. A good ND filter should not have any effect on the quality of the light. It should absorb all colors of light in equal amounts. In this way, ND filters reduce the low light sensitivity of the camcorder. This allows the camera to maximize the light handling characteristics of a film video camera. With proper lighting you will be able to create a more film-like look. This technique is also very helpful with depth of field issues, especially outdoors.

Diffusion filters are becoming very popular in helping to creating a more film-like look. The best way to find a good diffusion filter that you like most for your story is to try one. If results are less than desirable you can try something else. One word of caution is to be aware that the “one size fits all” diffusion filter is a myth. Depending on a cameras chipset, processor, menu settings and the user’s abilities, a filter that works well on one model may perform poorly on another.

You need to select the right diffusion filter for your particular camera and setup. Most manufacturers have come out with new types of diffusion and warming filters for HD. I suggest you experiment with them or talk to people at the various companies to ascertain whether a particular filter works best for your camera.

Here is one last story about issues caused by HD that reach beyond the working professional all the way to the amateur:

I got a call from a dealer who had sold one of the “prosumer” HD cameras to a doctor/lawyer type. It seemed that he shot a few hours of his family vacation at the beach. When he came home and plugged the camera into his 52-inch LCD TV, his wife and younger daughter would not watch the results. Even he had to admit that the images were “too perfect” in that they showed every imperfection and blemish. Obviously the days of a prosumer simply setting an HD camera on auto and shooting are at an end. I told the dealer to show the guy how to use the manual settings and to use a warm diffusion filter that I knew worked very well with that particular camera. We do not know how the resultant video came out, but the guy has not been back to return the camera.

Working with filters can solve many problems created by the new cameras and formats. But more than that; working with optical filters can bring you closer to your craft at the moment the image is being recorded. It gives you the best possible chance to create the image you want to create, to tell the story you want to tell in the most pleasing and dramatic way possible. So… get some filters and have some fun!!

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