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Zooming in the Fast Lane

Posted on March 30, 2016

Time was when zoom was a feature you looked at when evaluating moving fixtures. Although zooming capabilities are still critical in moving spots and washes, they’ve become increasingly important is static washes too. There’s a good reason why zoom is the focus of such intense interest: it greatly expands the versatility of a fixture, allowing you to do more with fewer units in easier to transport rigs.

Ford Sellers, Senior Product Manager of CHAUVET Professional offers an inside look at how zooming works, along with some valuable advice on evaluating zoom features. As Ford points out, judging a fixture’s zooming capabilities is seldom cut and dry. Like so much in lighting, the “right zoom” depends on your intended application for the fixture.

How would you define “zoom” or variable focus?
“The ability for a lighting fixture to ‘zoom’ is simply varying the projection angle. This has been common in both moving head spots, and washes for a long time. More recently, we have been including this feature in our “static” washes, too. The field angle (as opposed to the beam angle) is typically used to express Zoom range, as the overall size/coverage of the projection is what most designers want to know when working with Zoom as a parameter in their fixtures.”

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From a product design standpoint how does zoom work?
“Basically your optical system needs to include a moving lens which allows you to tighten or spread the beam as necessary. The issue from a product development standpoint is that zoom optics are most efficient in certain range (for instance 3:1 in most spots and profiles, 4 or 5:1 in many wash lights, or, in the case of the COLORado 1 Solo 10:1). In terms of designing a fixture, you need to consider how much extra space can be incorporated into the unit to allow the lenses to move.

“This means that as developers, we need to understand at what throw distances our customers are likely to use the fixtures. Once we know this, we can choose the proper number of LEDs, and the most efficient optics to generate the necessary beam and field angles for these applications. Also, for most applications a motorized zoom is required, as it is very common for a designer to want to adjust the angle during a performance. As a result, we need to allow space and control circuitry for the motors as well. Our goal is to give our customers a great tool that can be used as an area wash, a special, or even for a beam effect. We also want to allow for things like and a zoom chase, which can be a very effective dynamic effect. Ideally, we are trying to give designers the most flexible tool to match their most common applications.”

From a product design standpoint how does zoom work?
“This means that as developers, we need to understand at what throw distances our customers are likely to use the fixtures. Once we know this, we can choose the proper number of LEDs, and the most efficient optics to generate the necessary beam and field angles for these applications. Also, for most applications a motorized zoom is required, as it is very common for a designer to want to adjust the angle during a performance. As a result, we need to allow space and control circuitry for the motors as well. Our goal is to give our customers a great tool that can be used as an area wash, a special, or even for a beam effect. We also want to allow for things like and a zoom chase, which can be a very effective dynamic effect. Ideally, we are trying to give designers the most flexible tool to match their most common applications.”

What are the most important things a designer should look for when evaluating a fixture’s zoom features?
“Typically, there are three points that a designer wants to pay close attention to when evaluating the zoom feature in a product: zoom angle, brightness and color mixing.”

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Can we break those points down? Elaborate on zoom angle for us.
“When evaluating zoom angle, you have to ask yourself ‘What do I want to do with this fixture?’ Do you want a fixture that can be a small area wash, and a beam effect? If so, you need something that zooms down to about 5°, and out far enough to be useful in your space. Alternatively, maybe you need a fixture that can start as a large area wash, and isolate down to a special, in which case smooth zooming at slightly larger zoom angles will be your best choice. If you want to have a flexible wash light for various throw distances (maybe as a wash light for rental or in a facility that has several different performance spaces), then you need to know what those distances are – plus you’ll need to make sure that the angles that the fixture you’re looking at can give you the coverage you need to light your performers.”

What about brightness? How should I evaluate that when considering a fixture’s zoom capabilities?
“It’s important to know not just how bright the fixture you’re considering is, but also how bright the fixtures you plan on using it with are. A wide zoom range won’t do you much good if you’re only getting 30 lux at your most common throw distance and zoom angle. A 40 W LED fixture with zoom may not mix well with your 1200 W moving heads. Designers need to look at their application, and decide if the brightness of the zooming fixtures that they are looking at are going to be effective in their application.”

That leaves us with color mixing; how do you consider that when evaluating zoom capabilities?
“The optical design of LED sources make color mixing a challenge. Color mixing in a zooming optic is even more challenging. Generally speaking, the further your fixture is from the object being lit, the better the color blends. However in zooming systems, this is not always the case. On a typical quad color there are actually four different areas on the surface of the LED which each generate a different color of light. Since each color is generated on a different part of the chip, the individual colors will begin to separate in your projection when you tighten the beam angle too much.

“On top of this, you have to consider that different wavelengths of light have slightly different coefficients of diffraction, which means they are bent at slightly different angles as they pass through a common media, like a lens. Then you can begin to understand how maintaining good color mixing in a LED system with variable beam angles can be a challenge.

“Also as you add multiple LEDs to make the fixture brighter, the color separation can be even more apparent. Recently, we have made great strides in our optical designs as you can see in fixtures like the COLORado 1 Solo. Also, strides have been made by LED manufacturers to increase efficiency and power, so that we can make brighter fixtures with superior color blending.”

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Speaking of the COLORado 1 Solo, we hear a lot about its ability to zoom. Why is that? Is it particularly difficult to incorporate zoom into the design of single source LED fixture?
“The COLORado 1 Solo generates a homogenized beam. This means that when the performer looks up, they see what appears to be a single, large source, like they are used to seeing from traditional incandescent sources. Taken by itself, this feature would have put the COLORado 1 Solo right at the cutting edge of today’s technology. However, we also developed a custom zoom mechanism which combines several of the previous optical design advances to make the very first zooming fixture with a homogenized, single source appearance. This was made possible by the combination of our optical system with the latest advances in LED power. This combination of technology allowed us to make a fixture with a nearly unprecedented zoom ratio of 10:1, while maintaining perfect color mixing throughout the entire range from a 4 to 40 degree beam angle.”

From a practical standpoint, is there anything that a designer loses in terms of output, focus or anything else when using a zoom feature?
“Yes, and no…you don’t lose anything in the way of focus, but when it comes to brightness, there is something called the inverse square law that we always take into account. Basically, as the coverage area increases as a result of a change in the beam angle or a change in the distance between the fixture and target, the apparent brightness decreases. This is true even though the amount of light remains constant. If you think of light like paint, you can see that if you use the same amount of paint to cover a larger area, it will go on thinner. Light works the same way.

“Because the area expands in both the X and Y axis (it gets taller and wider, as you zoom), you take the inverse square of the ratio of your beam angle to get the brightness. For instance, if I double the diameter of my coverage area, I decrease my brightness to ¼ of the original value. If I triple it, it is one 9th, etc. When you do this by varying the distance between your source and target, the math works perfectly. When you do it in a zoom optical system, the math can be close, but usually there is some variance. This is because every optical system is more efficient in certain beam angles. In the case of the COLORado 1 Solo, we opted to make the “sweet spot” toward the wider end of the zoom range, to help with the apparent brightness at wider angles. So, at 4°, you get a tight beam, and a maximum output of 4,000 lux at 5m. This is extremely bright, and can be used as a beam effect on many stages. As you zoom out, the optical efficiency increases slightly, so that by the time you reach 40° (10x the beam angle), you are not at 40 lux at the same 5m distance, but at 75 lux (nearly double). This allows the unit to act as a very good wash light (its primary function), as well.”

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How are the zoom features in Chauvet fixtures most often used?
There are two primary ways. Firstly, zoom is used to make the fixture more flexible. You can use the zoom feature to light a subject from a very short distance, or, you can zoom it in, and light a subject from a much further distance. This means that you can use the fixture as a wash light in a variety of applications without having to change lenses, or add diffusion. Alternatively, the fixture can be zoomed all the way in, and used as a beam effect on stage similar to old-school ACLs.

“Secondly, designers can use the zoom as a dynamic effect. It can be used to isolate lighting to a specific spot on the stage. For instance, rather than creating a dramatic moment by fading up a special and fading down your area lighting, you can simply zoom-in on the center of your area. This essentially allows one fixture to take the place of two. Alternatively, the fixtures can create a huge amount of visual interest by simply changing from an aerial beam effect to a wash effect, or having the fixtures chase a zoom effect on your stage. The COLORado 1 Solo has an incredibly fast and quiet zoom mechanism. This allows for really incredible dynamic effects, or for a single fixture to be used to fad down in an area wash, and up as a special, with almost no dwell in your blackout.”

Can a zoom feature be over used?
“Yes – any feature can be over used. As an effect, the first time an audience sees it, they may be surprised. If it is used as an effect continually, it may become less interesting. In my view, any designer should be careful to choose the right moments when using a dynamic effect like zoom. However, using the feature to expand the number of applications in which you can use the same fixture never gets old. Not having to change lenses, or choose different fixtures because your truss has a different trim height in the next venue saves in both labor, and in the amount of equipment you need to haul around with you on tour. Having a single fixture in your rental inventory that can light a subject from 5 feet, or from 30 feet, means that you can get the most out of your gear. You don’t need to purchase three fixtures to have for short, medium, and long throws, because the zoom feature allows the same fixture to do it all. Being able to use the same fixture as a beam effect, and to wash a stage…well, that never gets old.”

Any trends in the way zoom features are incorporated into fixtures?
“I guess the short answer is yes! Physically, we are working continually to make our zooming mechanisms faster, more reliable, smoother, and quieter. Philosophically, certainly zoom is a trend. Lighting manufacturers are recognizing the benefits that zoom offers their customers in terms of flexibility, so I think it is likely that you will continue to see more fixtures which incorporate zoom moving forward.”