When to use anNDfilter for video

ND filters are available in 2x, 4x, 8x, 16x, 32x etc all the way up to 8192x (and beyond in fact). Each increase in multiple signifies a 1 f-stop, or 1 EV difference in light registered by your cameras sensor. In photography terms, ND filters are quantified by their lens opening percentage, f-stop reduction or optical density. So in terms of lens opening percentage, a 2x filter represents 50% of the lens area opening or 1EV (1 f-stop) reduction, 4x represents 25% or 2EV (2 f-stops), 8x represents 12.5% or 3EV and so on.

Coherent was founded as II-VI Incorporated in 1971 by Carl Johnson and James Hawkey.[5][6] The name "II-VI" is a reference to the groups II and VI in the periodic table, since the company started its business by producing cadmium telluride (cadmium belongs to group II and tellurium belongs to group VI).[7] The company's first products included lenses, windows, and mirrors for CO2 lasers.[5]

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In the 1990s, the company began to grow both on its own and through acquisitions.[5] It purchased Litton Systems' silicon carbide group from Northrop Grumman in the 1990s,[5] Virgo Optics in 1995,[8] and Lightning Optical Corporation in 1996,[8] among others. The combination of Virgo and Lightning created II-VI's VLOC division for developing one-micron solid-state lasers.[8] Acquisitions in the 2000s have included Laser Power Optics in 2000; Marlow Industries in 2004;[9] HIGHYAG (75% in 2007[10] and the remaining 25% in 2013); Photop Technologies in 2010;[11] Oclaro's Santa Rosa, California, optics coating facility in 2012; Anadigics and EpiWorks in 2016;[12] and Integrated Photonics in 2017.[13][8] The acquisition of Avalon Photonics, Anadigics, and EpiWorks allowed II-VI to increase its production of vertical-cavity surface-emitting lasers (VCSELs),[8] important to 3D sensing technology; and the acquisition of Finisar Corporation in 2019 brought to II-VI Finisar's high volume 3DS VCSELs indium phosphide (InP) platform and its experience in integrating InP lasers with optics and electronics in transceivers.[8] Acquisitions of INNOViON, Ascatron, and some of GE's patents have expanded its business in silicon carbide substrates.[8] In 2022, II-VI acquired laser manufacturer Coherent, Inc..[14] and took the name Coherent Corp.

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Coherent Corp. is headquartered in Saxonburg, Pennsylvania,[18] located north of Pittsburgh in Butler County. The company has R&D, manufacturing, sales, service, and distribution facilities in 130 locations worldwide.[19]

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Carl Johnson served as II-VI's first CEO from 1985 to 2007. He stepped down as CEO in 2007 and was named chairman of the board, a position he held until 2014.[15] Johnson was succeeded as CEO by Francis Kramer, who had been president since 1985.[13] Kramer followed Johnson as chair in 2014, in addition to his duties as CEO, and continued as chair in 2016 when Vincent D. (Chuck) Mattera, Jr., became the company's third CEO.[8] In November 2021, Kramer transitioned from chair to Chair Emeritus, and Mattera was named chair and CEO.[16] In February 2024, Coherent announced that Mattera would retire, remaining in place until a successor is named.[17] Jim Anderson was named CEO in early June of 2024. He was formerly with Lattice Semiconductor Corporation (LSCC)

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Coherent Corp. (formerly II-VI Incorporated) is an American manufacturer of optical materials and semiconductors. As of 2023, the company had 26,622 employees. Their stock is listed at the New York Stock Exchange under the ticker symbol COHR. In 2022, II-VI acquired laser manufacturer Coherent, Inc., and adopted its name.[3][4]

ND Filters or Neutral Density filters are, in their simplest form, darkened glass that you place between your subject and your camera sensor and in the majority of cases they screw into your lens. They are called neutral density because the filter reduces all light wavelengths reaching your cameras sensor meaning colour reproduction is not affected. There are also graduated ND filters available but in this article we will cover the standard screw in type ND filter.

Another thing to bear in mind is the type of ND filter you choose. One word of advice, buy a good one. Cheap ones may lead to ghosting whereby the light reflected by your cameras sensor is re-reflected off the inside of your cheap ND filter, causing what can only be described as ghost effects on your final image. This is totally avoided by buying a pro quality filter.

The company held its initial public offering in 1987.[5] According to Carl Johnson, the funds raised by the IPO allowed II-VI to expand its zinc selenide manufacturing capacity.[5]

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To explain by example let us pretend we have a 4x (2 f-stop) ND filter at hand. If we set up our camera in manual mode and our settings are ISO 100, f/2.8 and a shutter speed of 1/250s without an ND filter and we are showing perfect exposure, when we place the 4x ND filter on the lens you should notice that your cameras built in light meter is now showing a 2 stop (2EV) underexposure for the same scene. So to ensure we get the same exposure we had without the ND filter we need to modify the lens aperture (open it up letting more light in), the ISO (increase it making the sensor more sensitive) or the shutter speed (slow it down letting more light in) or a combination of the three. Usually however it is the aperture or the shutter speed that is modified as the prime purpose of an ND filter is to give you more flexibility with these two camera settings. Using ND filters will allow a photographer open up their lens aperture fully in midday sun for a range of shutter speeds. It will also allow a photographer take 30 second long exposures in bright light without overexposing. If daylight portraits are your photo of choice then check out why you would use an ND filter to give you more flexibility with your aperture. Or if you are a landscape or long exposure photographer then check out why ND filters are used to control shutter speed choice.

One disadvantage of using an ND filter is that it darkens what you see through the viewfinder rather dramatically and depending on what type of filter you are using (16x, 32x etc) your camera may not be able to focus at all because it is so dark. Where aperture considerations are concerned this is not so much an issue as you are mainly using the ND filter in bright daylight conditions and should never have an issue focusing. However if you are using an ND filter for long exposures in poorly lit conditions then this can cause problems. Check out our other article on ND filters and shutter speed for ideas on dealing with problems like this.

The Saxonburg headquarters site was once the property of KDKA, the world's first commercially licensed radio station, and some of the original structures are still there.[20] In the 1940s, the site was expanded by the Carnegie Institute of Technology and the U.S. Nuclear Regulatory Commission to become a 400 MeV synchrocyclotron research facility.[21] II-VI acquired the property around 1978 and has further expanded the facility over the years.[22]