Archive for the ‘Equipment’ Category

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Rolling Shutter vs. Global Shutter: Just Learned Something New About My GoPro

Sunday, July 28th, 2013

On this rainy Sunday morning I was just sorting through images I shot during my recent trip to Greece, and I learned something new (and surprising) about my GoPro camera: even when shooting stills, its electronic shutter is rolling, not global. If you just thought “huh?”, then read on.

On a short flight from the island of Milos back to the Athens airport I set up the GoPro on a suction cup mount pointing out the airplane window to do little timelapse of the flight. Looking at one of the still frames from the timelapse, I saw this:

GoPro still frame shot out the airplane window. Well, I guess that answers that question!

The above image is not Photoshopped in any way (other than the watermark). “What in God’s name is going on with that propeller, the blades are split in pieces!” you might say. Photographers, videographers and some others knowledgeable about electronics will know immediately what is happening here. The propeller blades did not, in fact, break into pieces during my flight (thankfully); the blades appear this way in this image as a result of a curious side effect of the way certain digital camera sensors work called “rolling shutter.”

Digital cameras’ sensors are composed of millions of individual pixels arrayed in a grid of rows and columns. DSLR cameras have a physical, mechanical shutter that starts and stops the collection of light hitting the sensor, but other types of cameras (point & shoots, cellphone cameras, and cameras like GoPros) do not have a mechanical shutter, and instead start and stop the process of collecting light on the sensor electronically rather than mechanically; essentially the circuitry in the cameras tells the pixels in the sensor when to start and stop “looking.” On many cameras, the pixels start and stop “looking” the way you’d expect: all at the same time. Cameras that behave this way are referred to as “global shutter,” because the “shutter” (which is in fact just an electrical signal) acts globally, on the entire sensor at once. Some other cameras though (notably, most digital video cameras) use what is referred to as a “rolling shutter” in that instead of reading the entire grid of the sensor’s pixels at once, they read the pixels one row at a time: the camera records what the first (top) row of pixels “sees,” then the row below it, then the row below that and so on, on a “rolling” basis until it reaches the bottom row. This process happens in a fraction of a second, so it is usually fast enough that it isn’t relevant to the image, especially when recording individual, still frames instead of video.

But when photographing something that’s moving very, very quickly (like an airplane propeller at full throttle!) that fraction of a second during which the camera moves from recording the top of the image to the bottom matters: by the time the camera gets around to recording the bottom of the image, the subject recorded at the top of the image has already moved, so in the finished image you’re seeing the same subject recorded in different positions. With a spinning propeller, that results in images like the one above, distorted by the passage of time.

Many cameras use a global shutter when recording still images (as opposed to video) and I thought my GoPro did too. I knew the GoPro used a rolling shutter during video recording (that is quite common on all but the highest-end professional video cameras), but it turns out that it uses a rolling shutter during still frame shooting as well.

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Making “The Best Camera” Better – The iblazr Flash Unit

Friday, July 26th, 2013

Hi all! I’ve been out of the country for the last two weeks and just landed back in North America a day or two ago (with the jet lag I’m having a bit of trouble keeping track of days…!) so things are incredibly busy around here at the moment, but I wanted to do a quick post about this very quickly:

In the photography world the saying has been going around for a number of years that “the best camera is the one that you have with you.” In other words, the best, fanciest, most expensive SLR camera in the world is useless if you don’t have it with you when you want to take a photo (and since most pro-level cameras are large, heavy and bulky, we tend not to have them with us all of the time). The cameras that most people do now have with us all of the time are the ones in our phones (the camera-phone phenomenon has literally upended the entire photography world, with a recent statistic I saw saying that in 2013 over 99% of all the photos taken in the world will be taken on phones). While the cell phone camera is ubiquitous and convenient, since these devices are phones first and cameras second (even though some phones’ cameras have gotten remarkably good; I’m continuously impressed with the camera in my iPhone 5) they lack lots of features and functions of real cameras. With that in mind, a number of different companies have started making products to enhance the photo-taking capabilities of phones. Enter, iblazr.

iblazr in black and white colors. Photo courtesy iblazr lab.

iblazr is a Kickstarter project by some folks in Ukraine who’ve designed a small device that can act as an external flash unit or continuous light for iPhones, iPads, Android phones, etc. It plugs into the phone or tablet’s headphone jack, and four powerful LEDs sync with the phone’s camera function. The device even includes its own battery, so it won’t deplete your phone’s battery.

I just heard about iblazr today, and when I read the Kickstarter page, I ponied up fifty bucks to back it immediately. This device, if its designers pull it off (and from what they’ve done already it looks like they will) should really help smartphones take much better photos in low light (the unit can even be used as an off-camera flash by using a simple headphone extension cord!). The Kickstarter funding period runs through September 3, so if this sounds like something you might like, go over to the Kickstarter page and get your name on the list and help this ingenious little product become reality!

The iblazr people estimate that they’ll have the finished units delivered in December of this year, so I’ll keep this post updated and give you my thoughts when I receive the product!

iblazr. Photo courtesy iblazr lab.

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How To Color Balance Mixed Lighting Sources

Tuesday, March 5th, 2013

I just finished a series of four blog posts talking about the various advantages and disadvantages of different types of lighting for photo and video work (the first post, with links to the others, is here), and why I’ve decided, for the time being, to use a mixed kit of fluorescent and LED lights. This kit is great and should serve my needs very well, but there is one hurdle that needs to be overcome first: while these lights are all advertised as “full spectrum” and “daylight balanced” at 5600K, in reality they all have visibly different color temperatures, so they need to be balanced with each other in order to work well being used together to light the same scene. In this post, I’m going to give step-by-step instructions on how I took three different lights with radically different white balances and balanced them to work together beautifully.

Before: Unbalanced

Before: Yuck. When white balancing for the mini LED panel on the left, the fluorescent softbox in the center is very green and the LED 1x1 on the right is slightly magenta.

In the image above, which I designed intentionally to exaggerate the color balance differences of the three lights, I placed (from left) a miniature LED panel, a fluorescent softbox and a 1×1 LED panel next to each other and aimed them at a uniformly white ceiling. The difference is striking (and awful).

Before: Yuck

Alternately, the same image above, only this time white balanced for the fluorescent soft box in the center, the LEDs on the sides are both overly magenta and orange.

As is, it would be very difficult to use these lights in a scene together without them appearing different colors. So they need to be balanced together. How to do this? Gels! Pulling out my collection of gels, I got to work.

I keep an assortment of gels to color balance pretty much anything (from left to right): CTOs, CTBs, Plus Greens and Minus Greens each in 1/8th, 1/4 and 1/2 densities. With this assortment, no matter which way a light is off balance, I can balance it.

Gels Gels Gels!

Gels Gels Gels!

In order to balance the three different lights (from three different manufacturers!) I started with the one that is most difficult to gel: the fluorescent (this is one of the biggest weaknesses of fluorescent lights in my opinion… they’re a pain to gel). I used that as my basis and then adjusted the other lights to match it.

It is possible to simply judge the color of a light visually in comparison to others next to it, like in the photos above, and to experiment with different gel combinations to get the lights to the point where they visually look the same to the eye, but “eyeballing” it like that is extremely difficult to do accurately; I have a very good eye for color (I scored a 19 on the X-Rite Online Color Acuity test! Take the test yourself, it’s fun!), and even I can’t achieve the level of precision that I want by eyeballing it. So to measure the color balance precisely I decided to use a couple of precision instruments: my camera and computer.

To start with, I set up a simple 18% neutral gray card on a light stand (I use this one from Amazon… it’s cheap and does the job well), along with a color chart. I lit the gray card and color chart with the fluorescent light (placing the light at an angle so that the light is illuminating the card but not reflecting glare). I then blacked out the windows in my office and shut off all the other light sources (overhead lights, computer monitors, etc.) so there was no “contamination” and I knew all the light hitting the gray card was from the light in question, and I took a still photo of the gray card and color chart with my Canon 5D Mark II camera in RAW format.

Gray Card and Color Chart

Gray card and color chart on stand for determining exact white balance of a particular light

I downloaded the photo onto my computer, and opened the file in Photoshop (you could also use Lightroom or any other application that can work with RAW files, I just happened to choose Photoshop). Using the White Balance Picker / eyedropper tool in the Adobe Camera Raw conversion screen (the same tool is in the Develop tab in Lightroom in the White Balance box), I sampled the 18% neutral gray card to set the proper white balance for the image, the values of which are then displayed in the white balance section on the right (it is a good idea to click a bunch of times in a few places on the gray card as the individual measurements will vary slightly, then average the values).

Sampling White Balance in Adobe Camera Raw

The White Balance Picker tool is the eyedropper icon near the top left. I sampled a spot on the neutral gray card, which gave me the white balance values shown in the white balance box at the top right.

Sure enough, I now saw numerically what I had seen visually on the wall: that fluorescent light was very, very green (+28 tint!). Since that is the light that was most off balance, ideally I would have gelled it to match the other lights, but since this light is so difficult to gel and the other are so much easier, I instead went the other way around and gelled the others to match this one.

With the temperature and tint white balance values for the fluorescent light in hand, I then repeated the process (blacking out the room, lighting the neutral gray card with a single light source, and shooting a photo) for each of my other lights and then found the white balance values for them as well (I found that my miniature panel has white balance values of 5100K temperature and -3 tint, and my 1×1 LED panel is 5050K temperature and +5 tint).

With that information, I then knew precisely how off balance my lights were from each other. I then added a gel to one of the lights, repeated the process of measuring the white balance values, and noted the numerical effect of a particular gel (bear in mind that as much as the gel manufacturers try to keep the color of their gels as pure as possible, a Plus Green gel will never be purely plus green…for example, my Rosco 1/4 Plus Green gels turned out to add +28 points of green tint, but also knocked off 300 degrees of temperature. But after measuring the color balance values of each light and the color effect of each gel, it was very straightforward to figure out which gels to add to each light to balance them together.

In the end, to balance my LED panels to my fluorescent lights, I needed to add 1/4 CTB and 3/8 Plus Green (one 1/4 and one 1/8) to my mini LED, and 1/8 CTB and 1/4 Plus Green to my 1×1 LED, which, while not numerically perfect, got my lights as closely balanced as possible with 1/8th-increment gels. Now I can comfortably use all of my lights in the same scene together and be confident that their colors will be balanced and visually indistinguishable.

After: I've Brought Balance to the Force

After: I've Brought Balance to the Force. While I can still see differences on this uniform white wall, in practical use these lights will never appear unbalanced.

 

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Tungsten vs. Fluorescent vs. LED lights: Light Quality (CRI) and Conclusions (Post #4 of 4)

Monday, March 4th, 2013

This post is the last of a series of four comparing the advantages and disadvantages of different types of continuous lights for photo and video work. Here are the previous ones:

Post #1: Choosing Lights: Tungsten vs. Fluorescent vs. LED
Post #2: Efficiency (i.e., power usage) and Heat Generation
Post #3: Portability and Speed of Setup & Ease of Use

Light Quality (CRI)

When choosing a light source, the final (and perhaps most important) issue is the quality of the light that that light source emits; in other words, its spectrum, or “CRI.” As most people know, light is made up of a whole spectrum of wavelengths, which results in different colors (in terms of visible light, red light is at one end of the visible spectrum with long wavelengths and blue is on the other end, with short wavelengths). Different types of light sources (LED, fluorescent, tungsten incandescent, HMI, the sun) emit different mixtures of wavelengths of light, and the best ones, like the sun, emit a nice, broad, even spectrum of wavelengths (without large spikes or dips at any given wavelength), which allows objects of different colors to appear as vibrant as possible in a photograph or video.

Color Rendering Index (or “CRI”) is a measure of the mix of spectrum that a light emits. This is the biggest advantage of the traditional xenon and tungsten lights: they emit the broadest spectrum of light of any of the types of photo and video lights here (this is because they closely mimic the behavior of a concept known to physicists as “black body radiation.” If physics is your thing or you really want to understand this subject in depth, read about black body radiation and Planck’s law). As a result, tungsten and xenon lights have the highest CRI (100, or close to it). LED and fluorescent lights, on the other hand, emit light that contains more of certain wavelengths and less of others (uneven spikes and dips), and therefore have lower CRIs (from as high as 95+ for good quality lights to as low as 60-70 for low-quality lights). The effect of lower CRIs is that some colors, including skin tones, can appear muted, washed out or unnatural in photos and videos. For this reason it is essential to choose lights with high CRI values.

Both my LED panels and my fluorescent lights have CRI values above 90. That is, they emit a quite broad spectrum of light that will illuminate objects of all colors well (that is not to say that they are accurately color balanced or white balanced for any particular target: CRI and white balance are two completely separate issues… more on that in tomorrow’s post). To illustrate the broad spectrum of light from each of these sources, take a look at the images below.

Emission Spectra ©2013 Chris Conti Photography

The emission spectra of my 1x1 LED panel (left) and fluorescent lights (right). Both show good, broad, consistent output. ©2013 Chris Conti Photography

To make the images above, I projected near-parallel beams of light from my LED (left) and fluorescent (right) light heads into an optical prism, which refracted the light into its constituent wavelengths, and photographed the results. Note that all of the colors of the visible light spectrum are well-represented. This is an indication of the high CRI value of these lights.

 

Conclusions

After experimenting with and testing various lights both in theoretical tests like the emission spectra above as well as practical ones like lighting a white seamless with them, using them for portraits, etc., I’ve made a few conclusions. In no particular order, here goes:

- The concern that LED and fluorescent lights emit poor-quality light as compared to tungsten lights is unfounded. With a tiny bit of adjustment via gels (more on that tomorrow) both from a subjective standpoint (how they look) and a technical standpoint (technical measures of their light emission), these lights look great.

- Both LED and fluorescent lights consume a tiny fraction of the amount of power that tungsten lights do (which makes them more usable in the field), and don’t generate the searing heat of tungstens (which is always inconvenient and can be destructive and painful, and uncomfortable for subjects).

- On the other hand, fluorescents and LEDs don’t generally generate the quantity of light that most tungsten heads do, so it may be necessary to use more of them for certain applications (flooding a white seamless, much less a full cyc wall, requires a huge sheer quantity of light), so these lights might not be terribly well-suited for these applications.

- Fluorescent lights are much less portable and more time-consuming to set up than tungsten lights, but LEDs are easier and faster.

- Light modifiers and accessories like softboxes don’t really exist for LED panels yet (although I did just make a softbox for my 1×1 LED… perhaps that’ll be a future blog post…), but fluorescent heads can usually easily accommodate anything mounted on a standard speed ring.

So what does it all mean? These lights are tools (just like all of our other kinds of gear), and they each have advantages and disadvantages, and are better suited for some tasks and worse for others, and the right tool for the job will depend on the particular job: lighting a large stage with a two-wall cyc wall is still best done with high-power, high-output tungsten or HMI lights. A quick location interview is probably best done with a couple of LED panels. For a small- to medium-sized studio shoot, fluorescents are probably the best bet.

Tomorrow I’m going to be going to a location and shooting in the same room all day. What will I bring? Fluorescents and a couple of LEDs.

I’ve learned a lot experimenting with all these different types of lights. If you’ve read this blog post and the few that came before it, hopefully I was able to share some of that with you. If you have any comments, different opinions or questions, let me know!

-Chris

P.S.- Since I’m going to be using a mixed bag of different light sources that result in a mixed bag of  color temperatures, in order to work well together the lights need to be balanced to each other. Balancing my mixed bag of lights will be the subject of tomorrow’s post…

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Tungsten vs. Fluorescent vs. LED lights: Portability and Ease of Use (Post #3 of 4)

Thursday, February 28th, 2013

This post is third in a series comparing the various types of continuous lights for photo and video work (it’ll definitely make more sense if you read the previous ones).

Post #1: Choosing Lights: Tungsten vs. Fluorescent vs. LED

Post #2: Efficiency (i.e., power usage) and Heat Generation

Portability

This is also something that is less important for photographers and videographers who work primarily in a studio, but for someone like me whose work is almost entirely on location, it is important. Tungsten and HMI light heads are usually relatively compact, but they are fragile; the bulbs are made of very thin glass and even thinner filaments, and can break if jostled around too much (especially if they’re cold, as tends to happen here in the northeast in winter). Also, since tungsten and HMI lights get so hot when they’re in use, at the end of a shoot they need to have a fair amount of time to cool down before being packed away or they’ll melt case fabric or padding or cables, gels or whatever else they happen to come in contact with in the bag or case… and a melted plastic power cable just sucks.

Fluorescent light heads have got to be the worst when it comes to portability. Since they don’t get hot you don’t have the issue above, but instead the bulbs are larger, bulkier, and even more fragile. My 3-head fluorescent kit is HUGE, because the bulbs are so fragile they need to be transported in individual cases (and with five bulbs per head, that means I’m carrying around 15 bulb boxes in the kit).

Definitely better in the studio: moving fluorescent fixtures is a huge pain.

Definitely better in the studio: moving fluorescent fixtures is a huge pain.

I can drive my fluorescent kit to a location, but don’t even think about flying with it… the kit is bigger than airlines’ maximum allowable suitcase size, and even if you could get it on the plane, by the time you picked it up at baggage claim all the bulbs would be shattered anyway.

And then there are LEDs… oh, blessed LEDs. LEDs are tiny, compact, rugged and oh-so-easy to travel with. Since they have no bulbs and no glass, LED panels are by far the most durable and least fragile of the lights here. Advantage, LEDs.

Speed of Setup and Ease of Use

Speed of setup is another issue that studio dwellers probably aren’t terribly concerned with, since lights that live in a studio frequently can stay set up and don’t need to be broken down between shoots. But for those of us always on the go it is a consideration. And here once again, fluorescent heads are the clear loser. Setup of tungsten and HMI heads is pretty straightforward: you put the head on a stand, plug it in, attach whatever modifiers you want to use, and you’re good to go. Takes a couple of minutes per light, tops. With fluorescent heads though, it’s a different story. In addition to all of the same steps you’d take with a tungsten head, with fluorescent lights each individual bulb (of which there can be anywhere from three to six per head, depending on the model) has to be carefully removed from its case and carefully installed into the head before any modifiers are attached, drastically increasing the setup time. LED panels, on the other hand, couldn’t be simpler to set up. You stick the panel on a stand and plug it in. Done. One of these lights can literally be set up in under 30 seconds. Advantage, LEDs.

Usability is a much more complex question (and a really important one). Here, tungsten and HMI lights really benefit from having been around for far longer than LEDs and fluorescents. The design of tungsten and HMI heads have been refined over years, and a whole universe of accessory modifiers have been developed to work with them: Fresnel heads use a lens and a moving focusing mechanism to allow light from these heads to be tightly focused into a spot or allowed to spread more flood effect. All manner of modifiers (umbrellas, snoots, gobos, softboxes of every conceivable shape and size, etc.) have been designed for these lights, and as a result they are extremely versatile. Fluorescent and LED lights, however, unfortunately are still new enough that for the most part these accessory modifiers are not yet available for them. Additionally, the design of most of these lights prevents them from benefiting from Fresnel-type housings, so their beam tends to be very wide (although a couple of companies are just starting to make LED Fresnels… take a look at these Arris). As a result, the light from panel-type LEDs and most fluorescent heads disperses quickly, so these lights tend to have short “throw” distances. Coupled with the lack of modifiers, this limits the versatility of LED and fluorescent lights. I am certain that modifier manufacturers will quickly start designing softboxes and other accessories for them, but for the time being, this leaves fluorescent and LED lights at a disadvantage.

Tomorrow’s post, the last in this little series, will look at quality of light emitted by the various types of light (the CRI), and my conclusions.

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