7:56 amOff
X Sync Limit
When photographing on location, you might want to use flash to complement the available light, allowing you to have greater control over the exposure of the subject and its environment.
When the ambient light is rather dim, you might need to "drag the shutter" (use a slow shutter speed to allow enough of the ambient light to register on the sensor), while freezing the subject with flash—the flash lasting only a very, very brief moment. In this situation, your only potential problem, in terms of exposure, is having a flash that is too powerful, forcing you to figure out a way to limit its output (by using neutral density gels, for example).
Conversely, when the ambient light is very bright, such as when shooting in broad daylight, you might encounter many challenges. First, you will need to use more powerful flashes, otherwise their light won't be bright enough to be noticeable, in comparison to the available light. Second, you will need to use very fast shutter speeds, otherwise the ambient light will be too powerful—the shutter speed, in this case, will allow you to control the ambient light without affecting the flash exposure, since the flash is so fast as to be unaffected by the shutter speed.
1/60 second X sync (denoted by lightning bolt) on the shutter speed dial of a Canon AE-1 Program camera using a curtain-type focal-plane shutter
But there lies the problem: when using flash, you won't be able to exceed the "X sync" of your camera's shutter—a speed that is very often much too slow to control bright sunlight when using larger apertures.
So where is that X sync limitation coming from? It comes from the simple fact that for flash to register on the sensor, its burst must occur at the same time as the sensor is fully exposed to it. And what controls the exposure of the sensor? The shutter. Whatever type of shutter your camera is using, there are unavoidable physical limits to the speed at which the mechanical parts of the shutter can move. Since the flash exposure is usually much briefer than the speed at which the shutter can move, the limit in the fastest usable speed is determined by the speed at which the shutter can fully expose the sensor.
Most cameras today employ a focal-plane shutter, a shutter that is located just in front of the sensor and can fully expose the shutter no faster than speeds around 1/250 second, often slower. You might wonder why the X sync is so slow while it is usually possible to use exposure times as fast as 1/8000 second...
Rather than explaining it myself, I will let Ansel Adams do it, with an excerpt from one of his famous books:
Current focal-plane shutters usually consist of two separate curtains. As the first one travels across the focal plane it uncovers the film to begin the exposure, and the second curtain follows after a controlled interval to terminate the exposure.
At longer exposures the first curtain will open completely, and, after the measured delay, the second curtain then closes. As the shutter speeds become faster, however, the second curtain begins closing before the first has fully uncovered the film, thus following the first curtain across the film. The exposure is made through the slit formed by the two curtains, and very fast shutter times are possible. [...]
With electronic flash the pulse of light is very brief, in the range of 1/500 to as little as 1/50,000 second, so the flash must be triggered at the moment the shutter is fully open. This requirement presents no problem with a leaf shutter, since there is always a moment when the shutter is fully open, even at the fastest speeds. With a focal-plane shutter, however, the maximum speed that can be synchronized with electronic flash is the fastest at which the entire film surface is exposed at the same moment, usually 1/60 to 1/90 second with the curtain-type shutter and 1/125 second with the metal blade-type. Using electronic flash with a higher speed means that part of the film will be covered by one or both curtains when the flash fires, and only a section of the film will be exposed.
Ansel Adams, "The Camera", pp. 84, 86, Little, Brown and Company.
There's a reason some photographers pay a hell of a lot more for camera systems that allow the use of central shutters. Apart from focal-plane shutters having achieved faster speeds than the ones Adams was referring to in 1980, this basic principle has remained true to this day, no matter what you might have understood from David Hobby or Joe McNally's insights. If all it took to circumvent the X sync was to use low-powered flashes, a whole sweep of the photographic educational material would become meaningless.
Take a look at this video of a Nikon D3 in slow motion, where you can clearly see the rear curtain following the first without ever fully exposing the sensor (which is to be expected, at 1/4000 second). This video is also interesting for it demonstrates the full process of the aperture blades stopping down and the mirror (and sub-mirror) raising, the shutter curtains moving down, followed by the cocking of the shutter while the mirrors and aperture blades go back to their original position.
No, what David Hobby and Joe McNally are referring to when they talk about a way to use flash at faster-than-X sync speeds is, for example, Nikon's "FP" or Canon's "High Speed Sync" modes. The basic idea is that instead of sending a single flash, these modes send a rapid succession of flashes during the whole exposure so as to allow the sensor to be exposed to the flash throughout, even if only a small portion of the sensor is exposed at any point due to the use of a faster shutter speed.
Of course, because the flashes have to send multiple bursts of light, they cannot be used at their full power—there must be enough juice to flash during the whole exposure. As a consequence, they can only be used at a lower power, hence the frequent use of a multitude of flashes at the same time to compensate for the loss of power.
The key issue here is the fact that multiple bursts of light are emitted because the sensor is not fully exposed at any point, not the fact that the flashes are used at lower power. To be very clear: the power of the flash has nothing to do with the ability to use fast shutter speeds, but is only a drawback to be able to use this trick. Moreover, these special modes can only be used with proprietary systems, when the flash can speak to the camera—it is definitely not a trick you can achieve with any combination of camera and flash, and definitely not when using studio strobes.
Here is Joe McNally on the subject:
On a bright, sunny day, your ISO becomes (roughly) your shutter speed at f/16. Thus, ISO 200 translates to a 1/250th of a second shutter speed at f/16. Right there, if you notice, you are at the top end of your flash sync speed, with a small flash powered by four AA batteries. [...]
Auto FP high-speed sync is an interesting and valid alternative to having the flash launch a missile's worth of light in one pop. In this mode, you are asking it to make many, many small pops of light. It syncs up with the focal plane shutter (hence the FP) to burst tiny bits of light through the blades of the shutter as it exposes the scene. Effectively, the light stays on for the whole exposure, which is a very short amount of time. This bursting capacity enables the flash to stick with the shutter all the way to a speed of 1/8000th of a second, depending on the camera.
Somethin's gotta give, right? You bet. The power of your flash falls victim to the speed and repetition of all those little pops. [...] A way around this is to use a bunch of Speedlights [...].
Joe McNally, "Hot Shoe Diaries", pp. 256-257, New Riders.
Here is Kirk Tuck on the subject:
You're probably aware that most digital camera shutters can only synchronize with flash at shutter speeds of up to 1/250 second. [...] If you are using one of the more sophisticated flash and camera systems, you should also know about a nifty feature that can be helpful for shooting in sunlight with your flash. It's called "FP" flash, and it works like this: With your camera and flash set to handle FP [...], choose a shutter speed and aperture combination that works with the ambient light and the flash will actually pulse consistently enough to light the camera sensor evenly as the shutter opening travels from side to side or from top to bottom. This technique is best used to supply a bit of fill flash when you are using a fast lens near its widest aperture to blur a background. Since the flash must pulse instead of unloading one big burst of light the output is much lower.
Kirk Tuck, "Minimalist Lighting", pp. 68-70, Amherst Media.
And here's a bunch of Wikipedia articles, all speaking with the same voice:
Today, certain modern xenon flash units have the ability to produce a longer-duration flash to permit X-synchronization at shorter shutter speeds. Instead of delivering one burst of light, the units deliver several smaller bursts [...]. This allows light to be delivered to the entire area of the film or image sensor even though the shutter is never fully open at any moment. The downside is that the flash is of less effective intensity since the individual bursts are lower powered than the normal capability of the flash unit. Only certain camera and flash combinations support this feature, and the camera-flash pairings are almost exclusively from the same manufacturer [...]
When using a focal-plane shutter with a flash, a photographer will typically operate the shutter at its X-sync speed or slower; however, some electronic flashes can produce a steady pulse compatible with a focal-plane shutter operated at much faster shutter speeds.
Focal-plane shutter — Breaking the X-sync barrier:
Electronics are also responsible for pushing the focal-plane shutter's X-sync speed beyond its mechanical limits. [...] At higher speeds, a normal 1 millisecond electronic flash burst would only partially expose the film – the part open to the slit. [...] In 1986, the Olympus OM-4T introduced a system that could synchronize a specially dedicated accessory Olympus F280 Full Synchro electronic flash to pulse its light at a 20 kilohertz rate for up to 40 ms, to illuminate its horizontal FP shutter's slit as it crossed the entire film gate – in effect, simulating long-burn FP flashbulbs – allowing flash exposure at shutter speeds as fast as 1/2000 sec. This allowed daylight plus fill-flash use in almost any situation. However, there is a concomitant loss of flash range.
12:48 pmOff
Color Models vs Color Spaces
There is a widespread—though understandable, to a point—confusion between color models and color spaces. For example, we'll hear someone saying something like "CMYK is much smaller than ProPhoto RGB", which unfortunately doesn't make sense because it compares apples with oranges, even if there's a certain truth somewhere in there. First, let's look at the concepts.
Color modes in Photoshop
There are a number of ways to express color. If we want to express "maximum red" (whatever that arbitrary color means), we might use the RGB model and say "255 Red, 0 Green, 0 Blue", but we could just as well use the HSB representation and say "0° Hue, 100% Saturation, 100% Brightness". Both would express the same abstract color ("the most red that can be expressed"), just as we could do using the CMYK model (0% Cyan, 100% Magenta, 100% Yellow, 0% Key).
In other words, there is nothing inherently limitative in expressing colors using different color models, it just speaks differently to different people or contexts. Photographers often find the HSB model more intuitive, while graphic designers (and people closer to the print industry in general) tend to be more comfortable thinking in CMYK.
Unfortunately, things are not that simple, because "maximum red" means a different thing to each device and medium. A typical digital camera can capture a much richer array of colors than a printer can typically render, so a color model alone is not sufficient to describe colors. If the computer were to simply ask the printer to render "50% Green", the printer would naturally wonder "Well, what do you mean by that?", because no two printer/ink/paper combinations produce the same color when they spurt 50% of their green.
Which brings us to color spaces. Of all the colors in the full spectrum (well, the portion meaningful to the human eye/brain at least—see Lab), a color space defines which portion of it it can describe and how colors are distributed. The subset of the full color spectrum that a space contains is referred to as its gamut. Therefore, the "maximum red" of a digital camera, LCD monitor and printer/ink/paper combination are all expressed the same way as (for example, in the RGB model) "255 Red, 0 Green, 0 Blue" in their respective space, but they don't mean the same color, because all of their spaces have different gamuts. "Maximum red" on a given monitor might only be, say, "73% Red" of a given camera (which has a much more vivid "maximum red"), so when we want to have consistent color across a workflow, we need to know the color space of each device we're working with so that they can all "speak the same language".
A color space that describes the characteristics of a given device is also called a color profile. In a complete digital photography workflow, we would therefore need a profile for:
- The capture device (the digital camera—or scanner, if we're feeling nostalgic)
- The display device we're working on (such as an LCD monitor)
- The output device (such as an inkjet printer/ink/paper combination)
We will also need to decide the color space (and bit depth, which can be thought of as the precision level) in which we will be performing post-production (also called, for obvious reasons, "working" space).
Photographers typically work in the RGB model (unless they want to perform old-school transformations in Lab) and typically deal with a number of familiar working spaces—sRGB, Adobe RGB (1998) and ProPhoto RGB.
- sRGB is a relatively small space that is the common denominator/standard for web publishing, so it should only be used when an image is exported for the web (or to some commercial printer that asks for it).
- Adobe RGB (1998) has long been the de facto working space because it is significantly larger than sRGB. The truth of the matter is that Adobe RGB has been smaller than the color spaces of digital cameras for years (see this ooold article), so when exporting images from the raw processing software to the Adobe RGB space you are throwing away lots of information. Worse than that, even modern inkjet printers can render colors outside of the Adobe RGB gamut.
- ProPhoto RGB is huge. While one could make the case that ProPhoto RGB might be too large in certain situations, when working in 16-bits, these concerns are not warranted. (ProPhoto RGB also happens to be the working space used by Adobe Lightroom.)
So, to wrap up...
A color model is the way you express colors. It doesn't have a size, and it cannot describe "real world" colors. It simply says "I am expressing colors using Red/Green/Blue channels", or "using Cyan/Magenta/Yellow/Key (Black) channels".
A color space (or color profile, or working space—all the same thing really, used somewhat interchangeably or depending on the context) is an actual description of a specific subset of the visible colors that maps—gives meaning to—the values used in a given model. Color spaces/color profiles/working spaces are all (typically) saved to disk in the form of ".ICC" files.
That being said, let's set the record straight on a number of color space related issues.
Using the camera profile as the working space
The camera's profile is quite large, but it is not the largest color space—not by a long shot. To give you an idea, here is a representation of the gamut of a Canon EOS 1Ds Mark II camera versus the ProPhoto RGB color space:
Comparison between the profile of a Canon EOS 1Ds Mark II and the ProPhoto RGB space.
Notice how abundantly larger the red mesh (ProPhoto RGB) is to the camera's profile (solid shape in the middle). The camera's profile is device-dependent to that particular camera and constrains colors to only the ones that that particular camera can capture, which has no bearing on how the artist would like to transform the image to bring it where he wants. The very bizarre idea of actually working in the space of the capture device is akin to caring that the final processed image will be "capturable" by the source device—it doesn't make any sense.
When working on an image, one should make abstraction of the source device. Imagine if a given photographer uses different cameras and wants to composite shots taken with different cameras in a single image? <head explodes>
The thing about CMYK
Because commercial printing processes typically work using color halftoning with CMYK separations, and because the default CMYK color profile used in North America is often U.S. Web Coated (SWOP) v2 (having a notoriously small gamut), we can be tempted to think that "CMYK is much smaller than ProPhoto RGB", which doesn't make sense. CMYK is a model, while ProPhoto RGB is a color space, so nothing can be said of the size of CMYK.
CMYK is not inherantly "smaller" than any other model, it's just that in practice, it is pretty much always true that any CMYK space used will be smaller than your working RGB space; let's just not confuse models and spaces.
Capture One
I find suspect the claim that "Capture One manages color better because it works in Lab". Let's understand that image transformations are mathematical abstractions that are only bound to a given space at the end of the process. Nothing prevents the internal image processing pipeline of a given software to juggle with imaginary colors of much greater precision than what can actually be displayed/exported.
Whatever happens behind the curtains, the "Lab" data has to be converted to a profile either to be displayed or to be exported to a baked file (e.g. TIFF, PSD, JPEG). In any case, it might very well be that internal algorithms used by Capture One manage to perform a "better" job with colors (I don't even know what it means to handle colors "better"—sounds rather subjective), but it would be for another reason than the fact that it does its math with L*, a* and b* coordinates.
5:30 amOff
Another Bunch of Web Concepts
Following a previous post, I kept hearing a discouraging amount of misinformation regarding some web concepts, so I thought I'd do as I did before and add my two cents.
Maximum Image Dimensions and Page Size
Alright, we all agree that we want our website to load rather quickly, because we know people aren't going to wait more than a couple of seconds. We also don't want mischievous people to be able to do much with our images. We have to consider the browser size of the bulk of our visitors when determining the size of our website, because we don't want to force them to scroll to see the whole thing.
These are all laudable objectives — I couldn't really disagree with them, in principle.
But 100-120 KB per page at most? 500-600 pixels wide images at most? That, I'm sorry, is based on egregiously outdated standards. Just so you don't have to take my word for it, I visited a bunch of photographers' web sites (they all happen to have blogs I follow) and looked at how large their images were — not the home page image, I mean the average image they present in their portfolio. You'll likely recognize these guys' name — I think they know what they are doing and/or have been professionally counselled.
The smallest images I found were those on Chris Orwig's site, and they were 693 pixels wide. Here's the rest of the random sample I visited:
- Joe McNally, 778 pixels wide
- Zack Arias, 804 pixels wide
- James Rubio, 819 pixels wide
- Drew Gardner, 826 pixels wide
- Chase Jarvis, 920 pixels wide
- Tim Tadder, 940 pixels wide
- Vincent Laforet, 1024 pixels wide
- Joey L, 1064 pixels wide
- Finn O'Hara, 1278 pixels wide
Wait, what? 1278 pixels wide? That's just the image, not even the website itself.
Do you have an idea what a single portfolio section of a site presenting such good quality imagery must weigh? A lot more than 120 KB. Did I have to wait an eternity to see the images, so much so that I thought I should give up and go to another site? Not at all. Do these guys really worry about their images getting stolen? Puh-lease.
I think I rest my case.
More on Image File Formats
Okay, so I'd already covered the key points in my previous post, but let's add some more information.
The idea that the PNG format came from PCs and never really caught on on Macs is simply baseless. The main reasons the PNG format was created were to improve upon the limited GIF format and to get rid of licencing issues (since GIF was patented by CompuServe). If anything, the Linux/free-software/open-source community (which was later, even before the OS X transition, largely embraced/encouraged/supported by Apple) did more for the format than the Microsoft-riddled make-everything-proprietary PCs. Indeed, Internet Explorer only recently got the memo that PNGs had an alpha channel, which is likely the main reason the format couldn't fully be exploited in the first place, hindering it's spread.
The idea that logos, which often use few basic colors, are prime candidates for the GIF format is only partially true. When you create shapes (be it in Photoshop or Illustrator) and convert them to raster images, new intermediate colors have to be interpolated to create seemingly smooth lines and curves — a process called anti-aliasing. The consequence is that even if you're only using few base colors when designing your logo, it might very well end up requiring more colors than can fit in an indexed color file format such as GIF. To be safe, go PNG, which is just as size-efficient, but not 8-bit palette limited.
The suggestion that you shouldn't embed color profiles in images to reduce file size is to be taken cautiously. If we all agree that images on the web should all be converted to the sRGB color space anyway (because we cannot presume color management will be available in the client's browser) and therefore don't decide to include the profile in our web images, well, it shouldn't really be a problem — if the profile is missing, every browser should presume sRGB, just as if color management was unavailable, so we're good. The risk, though, is that we some day forget that an image we export is for some other use (be it for a client, for a commercial printer that color manages, etc.) and then wonder why our images don't look as expected. Seriously guys, a color profile is about 2 KB — that's insignificant in comparison to the whole size of an image. Remove one step in your workflow and always embed color profiles, just in case; it's not going to hurt to do it, but it might if you don't.
The suggestion of creating a slideshow of photos using Photoshop's Animation functionality and exporting it as an animated GIF is preposterous even as a simple example. GIF is, as we know, a monstrously awful file format for photos, because it is 8-bit palette limited and will introduce screaming posterization or dithering. Furthermore, it will create huge file sizes because it is not designed to handle photos. Additionally, it won't allow (in any remotely economical fashion) transitions between images. Moreover, it won't allow any kind of control for the user (stop, pause, forward, back). Frankly, anything else would be a better idea — Javascript, Flash ... you name it.
Output Sharpening
I've already talked about the mistaken idea that the "Save for web" functionality would export smaller files. But what preparing images through Photoshop carelessly will also not do for you is screen output sharpening. Just save yourself the time and effort and error-prone procedure of doing that by hand the olde way and use something like Lightroom. (Or at least create yourself a batch action that also performs basic sharpening.)
Spacers
The dreaded "spacer.gif" (yes, this is the common name, not "single.gif") is a bronze-age-old hack. A trademark of poor code, of lazy development. There are other (better) ways to achieve what this shameless little bugger is doing.
If you don't mind the contempt you'll get for using it and still want to go ahead with the idea, keep in mind that images can be sized any way you want on a web page. This means that you should only create a single one of those darn things, one that is 1x1 pixel, and size it according to your needs on the page. For example, if you need a 600x400 empty placeholder, don't create a separate GIF file for the placeholder, just size your spacer pixel 600x400 at that location!
Alternate Text
You know the "alt" attribute of images? The idea behind that has absolutely nothing to do with search engines. Yes, of course, search engines will use whatever additional data at their disposal to enrich their databases and, hopefully, provide more accurate results. But that was not the motivation behind the "alt" attribute (which is required in strict versions of HTML).
The name says it: it is an alternative to the image, in case the image cannot be loaded or otherwise consumed. If the image is missing or there is any kind of problem, instead of showing the image, the browser will simply display the alternate text. If a blind person visits your website, not being able to see the images, their text-to-speech software will read the alternate text aloud. Therefore, the alternate text should be descriptive of what the viewer cannot see, not just a useless generic name like "image"!
Also, if you're using a spacer pixel (goodness forbid), you should include an empty alternate text (alt=""), otherwise if the text were to be called upon, it could break your design.
General notes on using CSS
CSS is fundamentally based on the idea of economy: the more global and the less specific the better.
What this means is that if you're going to be using, say, the "Verdana" font everywhere on your site,
- Proper CSS would call for defining "Verdana" only once as the font-family for everything in a single, global declaration. No need to mention it anywhere else, since this global declaration takes care of it all.
- Very bad CSS would call for redefining endless times "Verdana" as the font-family in each and every class you create. This not only means puke-inducingly redundant declarations, but also means that if you change your mind about the font used on your site, you'll have to go through every single darned class you've created and modify it. That's just about as far as you can get from the point of using CSS in the first place.
If you're going to use a property "everywhere, but", define a property in a global declaration (probably in the <body> tag or such an overarching location), then make amendments at very specific locations where the rules don't apply. This will dramatically reduce/simplify/tidy your CSS.
On the other hand, if you're going to use a property at a decidedly very specific location, don't define it at a global location, as it will affect every other use of the related tag/class. For example, I cannot see, for the life of me, any good reason to globally add a right padding to every friggin' link on the site if all you want to do is separate items in your footer. By doing this, you'll risk looking perplexed in front of 20 people when you won't understand why your thumbnails don't line up in their cells. Chances are that most links on your site are not going to benefit from a seemingly arbitrary padding on the right, even if some very specific ones might.
While I'm on the topic of padding a link... "Padding" is space inside an element, while "margin" is space outside an element. What this means, in the case of a link, is that even if the two properties would have the seemingly visually identical effect, the padding would make the link itself larger, while the margin would make the space next to the link larger. That is important, because if you're using padding on a link (goodness forbid), the "padded" section of the link would be active (clickable) as well:
Notice how empty space is active (bad!)
That's just wrong. The appropriate property to define, in that case, would rather be a margin.
Redefining Links with CSS
Alright, you want to redefine links (the <a> tag) so that they all look the same, except for the "hover" variant. So you're going to spend a couple of minutes duplicating your half-dozen properties four times in all of these variants so that they are all the same, except for the "hover" which will have a slight difference.
Since you've been reading what I said about global versus specific, you know that's no good. Instead of duplicating every-compound-thing from a:link to a:visited and to a:hover and to a:active (phew!), just redefine the <a> tag itself, once! Boom: all the links will share a set of properties defined globally. Then add only the differences you want to the "hover" variant. You're done. That takes less time and is more economic. Especially if you want to make a slight change afterwards — you won't have to make that change four times.
Lastly, be careful when removing the underline from links. You may want to do it for aesthetics reasons, but good design calls for good usability, not just cuteness. Make sure, if you remove the underline, that links are still obviously links. The underline is such an established standard that you should think twice before you do that — or just do it where it doesn't break usability, such as in a menu where items are obviously selectable, while leaving the underline for links elsewhere in the text. Also, don't use underline on text that is not a link (used purposely here) — that's very misleading.
7:04 pmOff
Notes on TTL Flash
Since there seems to be a lot of misunderstanding concerning the use of Speedlites (portable electronic flashes), I feel the need to bring some precisions. (Note that although a lot of functionalities, parameters and behaviors are similar from one brand to another, since I am more familiar with Canon equipment, there are times when it will be preferable that you look for additional information.)
What is TTL flash metering?
At first there was manual flash exposure, which meant that the photographer had to know the guide number of his unit and calculate effective distances against apertures and ISO numbers using the inverse-square law bla bla bla... For example, a flash unit with an (imperial) guide number of 100 would correctly expose a subject 25 feet away with an aperture of f/4 (because 100 = 25 x 4). And, oh, that's for ISO 100, and no, you can't see if what you just did was correct, because you're shooting film. Now calculate equivalences along the way, as you're shooting your event. Lots of maths, trial and error (but mostly error). Thank goodness, this era is long gone.
Then there was automatic flash exposure, which was calculated by the flash unit itself using a little photo cell. The flash would emit light and judge if enough had been emitted by the general amount of light reflected back. Needless to say, this was not very precise and could only hope to work when the flash was used on the camera's hot shoe. (Later versions offered a way to separate the photo cell from the flash unit so the flash could indeed be used off-camera, but this only solved part of the problem.)
Then, at last, came TTL flash metering. (TTL metering had appeared long before for ambient light metering, but was now also available for flash exposure.) Instead of letting the flash unit calculate if the proper amount of light had been emitted, it left that job to the camera, using exactly what it had seen "Through The Lens". The thing to remember, though, is that the core addition to TTL flash is not so much the fact that the camera and flash unit now talk to each other using more pins on the shoe (which it obviously has to, to achieve the result), but the fact that the metering is done by the camera, through its lens! The more the camera and flash can talk the better to automate the process and achieve more accurate results, but that doesn't change the core fact of who's doing the metering.
What's the focal length got to do with the flash?
The flash doesn't have to know what focal length is used to work properly, but by concentrating its beam on an area that is not wider than the area covered by the focal length, it can preserve its power that would otherwise be wasted to light areas not even seen by the camera. By doing so, it can actually improve its effective reach and illuminate more distanced subjects. This used to be performed manually with Fresnel adapters installed on the end of flash units, but is now fully automated — insofar as the unit is able to. (As a matter of fact, if you're using very long lenses (in wildlife photography, for example), you might be interested by accessories such as the Better Beamer.)
The image area, when using a longer focal length, is increasingly smaller than the area covered by a flash that doesn't concentrate its beam
The flash's zoom allows it to concentrate its beam to the meaningful area, improving its reach/conserving its power
That's all there is to it! The fact that each flash unit can cover different "zoom" ranges doesn't mean it stops working properly if the lens is set to a longer focal length, it only means it won't be able to concentrate further its beam, therefore not improving its effective range further. There is nothing you can do about it (apart from hooking an accessory to the end of the flash).
Why does the flash ignore the lens' focal length when aiming its beam anywhere but forward?
Well, this should be rather obvious: if you're not beaming in front of you with the flash, then whatever focal length you are using is meaningless for the flash, since its beam is no longer aimed in the same direction.
When you aim the beam to the ceiling, for example, what you're hoping to do is to bounce the light so that the (main) source of light now becomes the ceiling — at this point, changing the flash's zoom would mean beaming a wider or narrower spot on the ceiling, which has absolutely nothing to do with the lens' focal length. Setting the orientation angle of the flash head likely has a much more significant impact on the reach/effect of the bounced light than how wide the beam is on the ceiling, depending on how far it is, etc. Since the camera has no way of knowing how far the ceiling is (or if it is flat, etc.), there is no way it can decide how wide the beam should be. Therefore, it defaults to an average value — not the longest, because a small beam on the ceiling would mean harsher light, which is exactly what we are usually trying to avoid.
You can always change the flash's zoom value manually, if you so wish, but there is no question that linking the focal length to the flash's zoom when beaming anywhere but in front doesn't make any sense.
Additionally, with Canon Speedlites (I cannot comment on other brands, which I don't know as well), when using the included diffuser (the one that retracts inside the flash head), the flash's zoom automatically goes to its widest value — because the point of this diffuser is to achieve an extra-wide angle of 14mm (14mm being the widest lens available in the Canon lineup). This also means that the flash won't be as powerful, since it is spreading its beam much more.
Is the flash metering related to the focus point?
Since I am more familiar with Canon equipment, I cannot confirm for every other brand (check your equipment's documentation), but I would think that the behavior is very similar. With Canon cameras, ever since E-TTL II came along (that's a long time ago, circa 2004), flash metering is no longer linked to the autofocus point selected. This means that you can use the "focus-recompose-shoot" technique freely without worrying that the flash metering will be thrown off.
The metering will also use information from the focus distance (when available — this is a per-lens capability) to calculate its power. This means that if the focus distance is on a subject, it will likely expose the subject properly and pretty much ignore the background (which means potentially leaving it dark). If the focus distance is on a background, it will likely expose the background properly and pretty much ignore the subject (which means potentially overexposing it). Exactly what we would expect, considering that the in-focus area is likely the most important part to light properly.
What is the FEL button doing?
First, we have to understand that regardless of our usage of the Flash Exposure Lock (FEL) function, there is always a pre-flash when using TTL metering. Since the pre-flash occurs right before the actual exposure begins, it is hardly noticeable. (When using rear-curtain synchronization, the two separate flashes will be very obvious, because they will occur before the exposure and right before the end of the exposure, respectively, giving you plenty of time to see the two bursts.)
So the goal of the FEL is not to generate a pre-flash (that, we always get). The point is to lock the flash metering — exactly the way the auto-exposure lock (AEL) works with ambient light, but with flash. Why would you do that? Well, if you don't want the flash to be metered based on the final scene (because there might be something you anticipate will throw off the metering, such as a bright white background or, conversely, lots of black tuxedos in the frame), you can trigger the calculation on a different scene or on a specific area of the scene (by zooming in on a subject's face, or by using a different metering zone pattern, for example) and then recomposing-shooting, which will use the flash metering that was calculated before.
If you're systematically using the FEL before each time you shoot, ad nauseum, without significantly changing the frame, you are wasting your time (and battery power). I hardly ever use that function, but it can be useful in difficult situations — just as much as AEL is with ambient light (which I never use). Instead, I tend to prefer using exposure compensation, which I find more predictable.
Note that here, Canons and Nikons work rather differently. Canon's FEL locks the flash metering only as long as you hold the shutter release half-way (otherwise it forgets the flash metering after about 16 seconds, or very quickly after a shot). A little star (*) appears in the viewfinder as long as the FEL is active, and a new FEL will have to be be performed each following time you need it. Nikon's FEL (at least, the way I was told it worked) locks the flash metering for as long as you don't press the FEL button again — the flash exposure will be the same for all the following frames until you unlock it.
What about exposure compensation?
Like I was saying, I tend to prefer exposure compensation over FEL, because I can better judge how to tweak the exposure than by trying to aim at something that I think would be closer to what I want (good luck!)
There are two ways you can apply flash exposure compensation (FEC). You can either apply FEC on the camera, or on the flash unit itself. With Canon (again, I cannot confirm for other brands), if you apply a FEC on the flash unit, it overrides whatever setting was in the camera. I personally prefer applying FEC with the camera, because I can reach the button right next to the shutter release without even having to move my eye away from the viewfinder, and I see what I'm doing from the display at the bottom of the viewfinder.
To wrap up...
One thing is for sure, working with flash requires practice, because it is much less predictable (especially when bouncing off various surfaces). It gets particularly tricky when mixing flash with ambient light, because now you have two independent exposures to oversee, plus color balancing with gels, etc.
Get to work!
1:24 amOff
Camera Raw is not Just an Import Plug-in (Anymore)
Back in 2002, when Adobe Photoshop 7 came out, it featured a new plug-in called Camera Raw 1.0, to provide support for reading raw files. At the time, the functionalities offered by Camera Raw were very limited, and it was used basically as a mere import plug-in for raw files. Camera Raw started to be a more serious tool at around version 3 (with CS2), and by version 4 (with CS3) it had matured into a pretty powerful raw processor.
If you've been shooting for a long time and actually went through the transition from film to digital (I have not), you've had to relearn your post-processing workflow many times over to adapt to the rapidly changing technology. You've likely started to work with digital long before digital cameras (and raw files) even existed, and your basic workflow meant scanning negatives/slides into high resolution TIFF files and going straight to Photoshop to do all the processing. When serious digital cameras came out and you started using them, you've been told that raw files contained much more information than JPEGs (or even TIFFs, for some cameras used to optionally shoot straight to TIFF), so you've gladly begun shooting raw.
Now even you are advocating shooting raw to preserve all the information the camera can capture — which is good — but you may still see the raw processing step as a mere intermediary to Photoshop, where all the serious stuff goes down. You'll say things like "Well, you see, here you have all these sliders that you can play around with to change your exposure, white balance, curves and all — kind of a simplified version of the basic functionalities you get in Photoshop... But, you know, we are all eager to bring that file into Photoshop, a much more powerful tool anyway, so we'll go right ahead and press 'Open'." You'll then lecture on using the Threshold adjustment layer to find your black and white points, using Color Samplers to locate them, and use a Levels or Curves adjustment layer to set the clipping with the black and white eyedroppers — you won't fail to mention that one should probably aim for 10 black and 245 white at most, because printers cannot manage further extremes; you'll add a Color Correction adjustment layer to fix the color cast; etc.
Now that's what is known as old think.
Don't get me wrong; I'm not saying this won't allow you to achieve satisfactory results — go right ahead and use whatever you are more comfortable with. Daniel Malka said it best when he said: "If it looks good, it's good, right?" If you've been looking at Joey L's early work, for example, and have been blown away by the results he achieved, you wouldn't really care to know that his Photoshop techniques were, at the time, profoundly lacking (as even he acknowledges).
But still, if that is the way you see your typical workflow, you are missing out on what raw files have to offer; you haven't fully embraced the digital workflow to the fullest; you have kind of a half-assed approach to image processing that is tainted by your past experience; you aren't extracting all the detail you can out of your files. Even a 16-bit, ProPhoto RGB TIFF file only has a fraction of what the raw file has to offer, for the simple reason that as soon as you leave the raw file, you are working with a baked file: everything you'll do to the image from this point will be destructive, and you'll never be able to extract all the detail that was available in the source file. That's because a raw file has not been demosaiced, it's still in a linear gamma, and all the settings you play with are only parametric: they are not affecting "pixels" yet.
For optimal results, ideally, you should be doing as much of the work as possible on the raw file (be it using Camera Raw, Lightroom or any other raw processor) and only open the image in Photoshop once you've exhausted all the possibilities, for more complex local/pixel-level editing (when needed). Camera Raw and other raw processors now even provide some level of parametric local adjustments (especially since Camera Raw 5, Lightroom 2, etc.), so there is no excuse. The white and black points (referred to as "Exposure" and "Blacks" in Camera Raw/Lightroom) are particularly important, because you cannot recover blown highlights once the image has been baked, no matter the bit depth and color space...
But don't take my word for it. For an excellent primer on the raw processing workflow, you should definitely read the first three chapters of the Real World Camera Raw books by Bruce Fraser and Jeff Schewe — even if you're not working specifically with Camera Raw. (Note that Lighroom uses exactly the same processing engine as Camera Raw.) Or you can always watch one of the comprehensive video tutorials with Jeff Schewe and Michael Reichmann back at the Luminous Landscape.