When it comes to the finer points of ND filters and the resulting color shift, things can sometimes seem overwhelming. Here’s everything you need to know.Photo via Photography ElementPlaced in front of the lens, ordinary neutral density (ND) filters reduce light with no effect to image color or contrast while giving more control over exposure and depth of field. For celluloid film, ND filters only need to block light in the visible spectrum. However, many of today’s silicon-based digital sensors are sensitive to wavelengths the human eye cannot see, including the infrared spectrum, resulting in the need for “far-red” filtration as well.Without ND filters, the IR wavelengths are typically a non-issue. However, upon adding heavy ND, compensation for the IR spectrum becomes necessary. For example, if you add a 1.8 ND, providing six stops of non-infrared blocking exposure, you gain an imbalance in frequencies. In essence, your sensor is effectively being contaminated by the far-red, resulting in a muddy color shift across your image, particularly in the blacks and reflective synthetic materials. With proper IR filtration, however, the dark areas of your image are rendered crisp and clean.In the digital era, there has been a sizable array of ND options, but until fairly recently, no manufacturer has produced a truly neutral infrared ND filter. How is this far-red filtration achieved? There are a few different methods:1. DyesMany manufacturers will place a film of specialized green resin on top of (or sandwiched between) panels of optical glass. These types of filters are called Infrared Neutral Density Filters (IRND) and have been optimized for digital sensors. When light passes through the dye, it filters out an amount of the infrared spectrum by absorbing unwanted frequencies. Unfortunately, all IRND filters come with their own set of colorcast problems, and there is a varying degree of consistency across manufacturers and ND intensity.2. Hot MirrorsThe second method of infrared filtration is called a hot mirror. Hot mirrors are essentially infrared cut-offs and work through reflective interference: transmitting the shorter wavelengths and reflecting the far-red. Hot mirrors are made by placing fine dichroic coatings onto the surface of optical glass. Unfortunately, their high reflectivity is also a major drawback, as they have a tendency for ghosting. For this reason, they should be placed farthest from the lens in front of any other filtration.3. Carbon CoatedThe third and most recent form of infrared-blocking ND filtration utilizes a carbon metallic coating, which creates a truly neutral ND. The coating is bonded to the glass and provides impressively neutral color while blocking out infrared contamination. Unlike dyed IRND filters, carbon-coated IRNDs do not suffer from dye variance and thus produce the most color-consistent image available.Some digital sensors already have an amount of internal infrared filtration built in through the Optical Low Pass Filter (OLPF) placed directly in front of the sensor. So it is important that you research and perform tests ahead of time before deciding whether or not dyed IRND, hot mirrors, or carbon-coated IRND filters are right for your project.Here’s a great video from B&H that covers the basics of ND filter usage in both video and photography.Got any thoughts on ND filters? How many do keep in your kit? Let us know in the comments below!
Commonwealth Games plunged into deep trouble today after England admitted their participation is “on a knife-edge” while Scotland athletes delayed their departure to Delhi and Wales set a deadline of Wednesday evening for the organisers to certify all venues and Games Village are safe.A footbridge collapsed near the main venue of the Games yesterday, which injured more than a dozen people, and the desperate state of the Athletes’ Village — described by Commonwealth officials of some countries as “unfit for human habitation” — has cast major doubts over foreign athletes turning up in India.Should the Commonwealth Games be called off? To vote from your mobile, SMS
Roger Federer will begin his Olympic campaign against Alejandro Falla, the Colombian who almost humiliated the great Swiss at Wimbledon in 2010.Federer, who won a seventh Wimbledon title earlier this month, had to come back from two sets to love down at the All England Club to beat Falla in the first round two years ago with the Colombian losing his nerve on Centre Court when he served for the match at 5-4 in the fourth set.Top-seeded Federer, who is appearing at his fourth Olympics, has been placed in the same half of the draw as fourth seed David Ferrer, who will play Vasek Pospisil of Canada.”Federer is the favourite whenever he plays here,” said Falla.”I know him well and he knows me well, too. I’m going to have to play my best if I am going to have a chance to win this match but he’s Roger and he’s just won Wimbledon for the seventh year here.”Second seed Novak Djokovic, the 2008 Beijing Olympics bronze medallist, will challenge Fabio Fognini of Italy in the first round.Djokovic is in the same half of the draw as third-seeded Briton Andy Murray, who faces Stanislas Wawrinka of Switzerland.Fifth seed Jo-Wilfried Tsonga of France will meet Brazil’s Thomaz Bellucci, the recent Gstaad Open winner.Missing from the men’s draw is defending champion Rafael Nadal who pulled out of the tournament through injury.In the women’s singles, the Williams sisters both face tricky opponents in the first round.Wimbledon champion Serena, seeded four, plays Serbia’s Jelena Jankovic while Venus tackles Italy’s ninth seed Sara Errani, the French Open runner-up.advertisementSerena and Venus are two-time doubles gold medallists, while Venus also won the singles gold medal in Sydney in 2000.Top seeded Victoria Azarenka of Belarus is up against Romania’s Irina-Camelia Begu, second-seeded Pole Agnieszka Radwanska faces Germany’s Julia Goerges.Third seeded Russian, Maria Sharapova, the 2004 Wimbledon champion, plays Shahar Peer of Israel.There is a 64-draw for the men’s and women’s singles, with 16 players seeded in each event, and a 32-draw for the men’s and women’s doubles, with eight teams seeded in each event.Mixed doubles, which is making a return to the Olympics as a medal sport for the first time since the Paris Games of 1924, will have a 16-draw, with four teams seeded.The draw for the mixed doubles is being held mid-way through the tennis event on July 31.