AO is often paired with multimodal retinal imaging technology to aid in visualization of the posterior segment. AO has been paired with a number of existing ophthalmic imaging modalities including flood illumination ophthalmoscopy (FIO), optical coherence tomography (OCT), and scanning laser ophthalmoscopy (SLO) to reduce the effect of aberrations on retinal imaging. Some of its applications include, but are not limited to, the visualization of cone photoreceptors in healthy eyes, those with age-related macular degeneration (AMD), and those with inherited retinal diseases, the study of vasculature, particularly in patients with diabetic retinopathy, the tracking of leukocyte migration through retinal vasculature, and the imaging of retinal ganglion cells, particularly in patients with glaucoma. [3] [4]

The primary benefit of all of these imaging modalities is the ability of the user to visualize retinal structures in vivo on a cellular level. In terms of individual system benefits, they differ: AOFIO alone has been developed and approved for clinical use. In comparison to the scanning techniques of AO-OCT and AO-SLO, AO-FIO also offers a larger, and more rapidly acquired retinal image, reducing the procedure time. In contrast, AO-OCT notably allows for increased lateral resolution compared to other combined AO modalities and remains the most ideal for appreciating depth in the retina. Specifically, AO-OCT can aid in visualizing RGC, RPE, and choriocapillaris, which focus at varying depths. AO-SLO has demonstrated increasing utility in research as an excellent modality for visualizing cone photoreceptor inner segments, RGC, RPE, leukocyte migration in retinal vasculature, and single photoreceptors. [2] From a more clinical standpoint, AO-SLO offers insight into the physiology of conditions such as cone-packing density in healthy eyes, cone-packing density and vascular abnormalities such as microaneurysms in diabetic retinopathy, cone mosaic abnormalities in central serous chorioretinopathy (CSCR), early detection of drusen in eyes with AMD, and patterns of photoreceptor loss in inherited retinal diseases such as Stargardt disease and retinitis pigmentosa. [3]

Adaptive Opticsmirror

Adaptive Optics (AO) describes the use of wavefront sensors to sense aberrations of ocular optics, and to use deformable mirrors to compensate for the aberrations to enhance retinal imaging performance. While this technique was originally developed to reduce aberrations in Earth's atmosphere when gazing at the night sky, it has been modified and optimized for the visualization of retinal structures in vivo. [1] [2] Given its utility in retinal imaging, AO is currently under research for optimization in viewing cone photoreceptors (PR), retinal pigmented epithelial cells (RPE), retinal ganglion cells (RGC), blood vessels, and the optic nerve, among others. This article will evaluate different types of Adaptive Optics machines, analyzing advantages and disadvantages and the potential applications of each.

A four-leaf barn door mounted to the front brackets of the light can control the beam, for example. Round scrims — metal screens mounted in a metal frame — can reduce light intensity. A speed ring with a softbox can help create a soft, wrap-around light. Traditional tungsten Fresnels don’t come with built-in dimmers, but external dimming systems cost about $50. Blackwrap(TM) or CineFoil(TM) — essentially heavy, black aluminum foil — is useful for shaping light. Attaching Gels and diffusion elements using C47s (a.k.a. wooden clothespins) to change the color or intensity of the light.

How doesadaptive opticswork

If you want to see what Fresnel lights are truly capable of, do an image search for George Hurrell and you’ll see beautiful portraits utilizing Fresnel lights dating back to the early twentieth century. You’ll find these workhorses of the lighting world on sets and on location across the world, making the movies, television and news shows we watch daily.

Fresnel lights are also great for product shots where you need to light relatively small, immobile props from a distance. As mentioned earlier, many film stages will have a ceiling pipe grid filled with hanging Fresnels, usually controlled from a light board.

Imaging with AO-OCT resembles the technique used with AO-SLO. In fact, some AO-SLO machines combine SLO and OCT features to allow for both modalities to function in the same eye. In these machines, a scanning slow vertical mirror first captures a single SLO frame followed by a fast OCT frame in the vertical and horizontal planes, allowing for volumetric acquisition. [7] Within the broad category of AO-OCT modalities, several subdivisions fall under the technological descriptors of "time domain" and "spectral domain," which indicate the detection mechanism of the OCT signal. [5] AO-OCT is limited by motion artifact and fixation deficits of the patient, given its reliance on high-speed imaging and high magnification. Specifically, conditions including vitreous or aqueous opacity, age related related miosis, and loss of structural integrity to the retina may diminish the quality of imaging notably. [8]

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Fair warning: Never touch a Fresnel’s glass lamp. It doesn’t matter if it’s hot or cold. Even when the lamp is cool, your fingers will leave a small amount of oil on the glass. This will heat up when the lamp is in use. This can cause the lamp to explode, and they aren’t cheap to replace. They can also leave a nasty burn if touched when hot. Seventy percent of the energy used by a tungsten light is dispersed as heat, with only 30 percent visible as light. Use gloves when handling any tungsten lights.

For more free tips on setting up your studio production, check out our ultimate guide to setting up a video production studio.

Adaptive opticsastronomy

Fresnel lights can be expensive. Also, learning how to use them takes time. So, it can be a tough investment to justify without prior experience with the lights. They can also be heavy, making them tricky to transport. These lights probably wouldn’t be a good choice for on-the-go productions or productions that need lights that are quick to set up and disassemble. They need some time to cool down before packing up, so fast-paced productions may find Fresnel lights hard to work with.

Currently, all AO devices besides the rtx-1 AO-FIO device by Imagine Eyes are restricted to research use. [6] Implementation of AO in the clinical setting remains hindered by the cost and technical prowess required to run the system, the time investment of providers and patients needed to scan the eyes, the inconsistent quality of the images collected, and the lack of a standardized database to aid in interpretation of the images. [3] As a result, these challenges, among others, preclude the production of AO for commercial use at this time; yet, solutions are continually being pursued to overcome these difficulties in order to introduce AO into the clinical setting.

Adaptive opticstelescope

If you’ve ever taken a film lighting class, you should know about a typical three-point lighting system. Often used for interviews, three or four Fresnels can act as a key light, a fill light, a rim/hair/backlight and the fourth as an optional background light. You’ve most likely seen the results of thousands of these setups in just about any documentary with a sit-down interview or in long-form news television shows, such as “60 Minutes.” But this isn’t all that you can do with a few of these lights. With the ability to up the intensity and direction for use in more artistic situations, you can create a moodier atmosphere.

Many accessories can be added to Fresnels to further control their light. These are traditionally sold separately. However, some may be included with the new LED Fresnels (depending on the make and model).

Adaptive opticsexamples

Fresnel lights have a lot of good points. But like with any tool, knowing its strengths and weaknesses can help you make the smartest choice. Fresnel lights, when used correctly and in the appropriate settings, can lead to truly cinematic, professional video.

Augustin-Jean’s inspiration came from trying to reduce the weight of a large spherical lens. He did this by carving concentric rings — like the rings of a tree — in a flat lens. Each ring bends the light slightly more than the one beneath it. The results in the light rays all projecting as a beam. Outside of lighthouses and movie sets, Fresnel lenses are also used in car headlights and those large, outdoor event lights that shine into the night sky at movie premieres — like the one Commissioner Gordon uses to summon Batman.

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Adaptive opticsOphthalmology

Film set Fresnel lights are fairly simple tools and are quick to master. They come in various sizes and intensities and serve as a spotlight or a flood light. The apparatus itself is simple. A lamp (i.e., bulb) sits on a movable track behind a Fresnel lens and in front of a spherical reflector. The reflector directs most of the light towards the Fresnel lens, which then corrals the illumination into a beam.

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One of the most important things to know about a Fresnel light is how to pronounce it. There are few quicker ways to be labeled a “newb” (newbie, novice or newcomer) on a film set than by mispronouncing the light as FRAZ-nel. It’s pronounced “Fray-NEL,” with a silent “s.” The name for the light, or more accurately, the lens found in the lighting fixture, refers to the French engineer, Augustin-Jean Fresnel. He invented the technology for lighthouses in the early 1800s. His invention was so well received that he was nominated to be the commissioner of lighthouses in France.

In AO-SLO, AO runs inseparably from the imaging system, correcting aberrations in real time. One particular feature of this system's deformable mirror is its ability to perform optical sectioning by adjusting the focal plane within the retina, using the defocus control. The defocus control may be built into the closed-loop system, allowing for continuous imaging. [5] This device functions by focusing a single-spot beam on the retina and reflecting light through a confocal aperture, thought to minimize scatter. [2] While confocal detection provides excellent imaging of photoreceptors, other detection modes aid in the visualization of other retinal structures. To capture RPE, a "dark-field" mode may be employed; "off aperture" enhances light-scattering structures such as retinal ganglion cells (RGC) , and "split-detector" mode helps define the photoreceptor out segments. [3]

Encasing all of this is a housing that dissipates the enormous amount of heat the unit produces. There is a knob, usually in the rear of the housing, which is used to move the lamp/reflector team along a track. This allows the beam to be either spotted or flooded. There are usually four brackets on the front of the light — three fixed and one movable. These brackets hold barn doors, speed rings, scrims and other tools. Finally, there is an AC power jack to provide electricity and a standard stand mount and yoke to mount the light to a light stand or ceiling pipe grid. Simple, right? Trust us, they’re even easier to use than we just explained.

Fresnel lights can be found in studios around the world because they are both portable and durable. They are incredibly useful for location shooting and deserve a spot in every professional’s setup. Let’s take a closer look at these lights and why they’re so important in video production today.

First off, Fresnel lights make things look really nice on camera. They can emit light that’s either soft or hard, so they are highly flexible lights. Most directors of photography (DPs) seem to prefer the color of tungsten Fresnel lights to newer LED lights, as well as the control the traditional lights allow. However, while DPs often prefer tungsten Fresnel lights, LED Fresnels draw much less power and stay cooler. LED fresnels are also dimmable and can even switch between daylight and indoor light in color within their single unit.

For AO-FIO the patient sits facing the the machine with his or her chin on the chin rest and forehead braced against a plastic ribbon to steady the head. In order to optimize the consistency of the procedure and to mitigate blinking in the first frame, the patient fixates on a point and initiates the system with a button. The machine begins by rapidly assessing optical aberrations and correcting them with AO until they fall below a designated threshold. At this point, the camera collects an image. This sequence of aberration correction and image collection continues until a sufficient number of images are gathered. [5] [6] The main drawback of AOFIO remains its image quality, which often exhibits poor contrast due to the capture of scattered light from retina and choroid. [2]