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Focus and Zoom

Brad Schiller • Feeding the MachinesOctober 2019 • October 10, 2019

Automated lighting fixtures have many different features to assist in creating a multitude of looks on stage. Gobos, colors, prisms and animation wheels are just some of the standard tools of the trade. Two often over-looked features for affecting a fixture’s output are lens focus and zoom. By changing the size and clarity of the output, creative possibilities abound. Lighting programmers need to be familiar with using focus and zoom, and their related options and effects to maximize the effectiveness of lighting products.

‡‡         Concentrating on Focus

Obviously, focus is generally used to adjust the image clarity. Typically on a hard-edged unit, the focus will adjust the field from a sharp focus to various degrees of blurriness. Some wash fixtures also utilize a focus parameter to adjust the fall off of the light from the center to the edge or to make the edge clearer or softer.

Most lighting fixtures assign two DMX channels to the focus parameter allowing for a very fine 16-bit resolution of control. When you are dialing in the focus on something you want perfectly sharp, you might need to switch to a fine or ultra fine control of the parameter. This way, you can get the best clarity possible for a corporate logo or other specific image. Each console has a different method for fine adjustment, so be sure to familiarize yourself with your desk’s methodology.

As with color and position, it is a good idea to store focus values in a preset/palette for quick updating and reference. Remember that both the focus and zoom should be stored together in the same preset/palette as they are intrinsically related. There are some cases, though, where you might want to store them individually.

Many LDs prefer to use gobos slightly out of focus, instead of very clear imagery. The LD may take the time to get the focus exactly as he or she desires. Be sure to store this as a preset/palette and label it clearly. You don’t want someone thinking the blurry state is an accident. For example, many years ago, when Miss Saigon was first on Broadway, the LD had all the gobos slightly out of focus. A few years later, a new person came to the show and updated all the presets to perfectly sharp focus because he thought the cues were in error. In reality, he changed the entire look of the show, and the LD had to come back to correct this mistake. Perhaps if the focus presets had been labeled “blurry,” then the problem could have been avoided.

‡‡         Magnifying Zoom

The zoom parameter on lighting fixtures will enlarge or shrink the size of the output. This feature can be used to adjust the output size to match a specific need or as a manner to adjust the overall intensity. Remember that the lumen output will generally be greatest at the wider angles, but spread across more area. When zooming small (or tight), less lumens are generally available (due to optical qualities), but the output will be brighter as the lumens are packed into a smaller space.

Some fixtures have optical designs that allow them to focus on all the various components throughout the entire zoom range, while others may not be able to obtain a sharp focus at the narrowest or widest angles. In addition, certain effects may not be able to enter the optical path when the zoom lenses are in certain positions. For instance, a prism may interfere with the zoom lenses at the narrowest setting. The fixture software may prevent you from inserting the prism, or it may automatically adjust the zoom optics back to a safe location.

The zoom feature is moving large amounts of glass within the fixture, and thus zooming tends to be one of the noisier functions of a light. Keep this in mind when moving the zoom quickly as you may need to slow the movement down to be less audibly distracting.

At wide zoom angles, you might start to notice some curving of your imagery or shutter cuts. This pin-cushioning effect can be very annoying, and you may need to zoom the image smaller to eliminate it. It is always a good idea to test the zoom and focus ranges with various parameters when you first start working with a new fixture.

‡‡         Affects of Effects

Effects engines and chases can be tons of fun when applied to focus and/or zoom parameters. I like to apply random shifts to the lens focus for dramatic undulating looks. Note that you will need to adjust the effect size to be very small as large changes in the focus will probably not be desirable. Zoom chases are very powerful on stage as the beams change from one size to another. Some fixtures can accomplish this very quickly, while others move more subtly. It really just depends on the fixture’s optical design and internal software.

If you are after very quick changes to your zoom or focus, check to see if your fixture has a fast mode in its control channel. Often manufacturers will dampen the max speeds of parameters so a fixture performs quietly. However, if you change the default speed setting to “fast mode,” then you can usually drive parameter such as optics and pan and tilt much faster than normal. Basically, you are telling the manufacturer (and the fixture) that you are not concerned with the possible associated noise. Besides, you can always toggle the mode back to standard when quiet movements are required.

‡‡         Auto Focus

Another option you might find in the fixture’s control channel is an auto-focus or focus-tracking feature. Each manufacturer labels and handles this function differently, but the premise is the same. First you set your zoom and focus, as you desire. Then you enable the focus-tracking feature. Now, when you zoom the fixture, the focus will automatically track along without requiring any changes from you.

This sounds very reasonable and useful, and many programmers do like to make use of the function. However, there are several things you need to be aware of concerning this feature. First is that there is no optical analysis happing as in a camera with autofocus. Instead, the function works by applying mathematic algorithms regarding the distance of the projection and the relationship of the focus and zoom optics. When you enable the feature, you have to select an approximate throw distance. Usually the options are short, medium, or long. Then, as you move the zoom, the algorithm is applied to automatically adjust the focus based upon where it was when you previously manually adjusted it. Sometimes it is correct, but often the focus is close but not perfect. Only with a perfectly accurate measurement input into the algorithm could you expect flawless focus tracking.

Furthermore, using the focus-tracking feature means that the focus value from your console data is now ignored. Any preset/palettes will not apply, and therefore, cues may be more difficult to update. While a focus-tracking feature can be helpful in some circumstances, I personally shy away from it as I prefer to have the console in control of the fixtures and their parameters at all times.

‡‡         Seeing Clearly Now

Working with focus and zoom parameters may at first seem rather straightforward, but as you have just read there are many options and considerations. Before you start programming a new-to-you fixture, you should take the time to see how the fixture functions in regards to focus and zoom. Additionally, make note of any speed or focus tracking features and learn how they are implemented on your console. Once you understand how each fixture utilizes focus and zoom, then you can build creative looks and chases with ease.

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