Ed Schlotzhauer

An artists journey

Category: Photography

  • Unrecognized

    Unrecognized

    Sometimes things are right there staring us in the face. But we don’t or can’t see it. We fail to see what should be obvious. This in an internal problem. We don’t get to blame anyone else. Don’t go through life with unrecognized interest all around.

    Unrecognized artist

    “Unrecognized” is a fairly ambiguous word. Well, not really ambiguous, it is just that it can be applied so many ways. One of the first things that comes to mind when I hear the phrase is my sadness at being an “unrecognized” artist.

    Even though I have sales and good gallery representation and I get exhibited, it feels like nothing. Failure. I seek to be more widely known. A goal is to share my vision with many more people.

    But this aspect of “unrecognized” is not what I am discussing in this article.

    Unrecognized beauty

    Most people I know sort of drift through life in a daze. We follow our normal paths, doing basically the same thing all the time without really seeing things around us.

    If we recognize the rut we are in, we can climb out. At least enough to make a difference. Just deciding that we are going to pay more attention to things around us will go a long way.

    There is beauty all around us, even if you live in a city. Disappointed that you don’t live in Yosemite? Get over it. Learn to appreciate where you are. Even if you are not thrilled with your environment, by learning to look more closely we can usually find things, even little things, to brighten our day. Is there a flower, or a tree, or a pattern of light and shadow on a building that catches your eye? Look at it. Stop and take a moment to appreciate it.

    This will grow a habit of mindfulness. It will help us become more aware of what is there and more grateful of the little scenes that brighten out day, make us feel more alive.

    Unrecognized self

    Many of us, I’m pointing to myself, too, have trouble recognizing where our creative instincts are leading us. We change all the time. It can be hard if we feel like we are starting to be recognized for a certain style or subject. We fear that changing would lose our market. But at least that person is aware of what is going on. Most of us, I feel, one day realize that what we are drawn to is different from what we have been practicing for a long time. This can shake us to our bones. But it can also be refreshing and invigorating to re-align with where our subconscious is directing us.

    I think this quote from a very good photographer from the past, David Vestal. is enlightening.

    As we work, we come to know more and become more patient and less inclined to rush past our own work that we don’t yet recognize. Now I am quicker to see in my own new work the “accidental” good photos that I used to ignore.

    Mr. Vestal points out 3 key things that are common and key to our artistic growth.

    Know more

    As we practice our art we learn. Our technical abilities grow and our creative capabilities are stretched. The more we learn the deeper vocabulary we have to express what we see and feel. We also have more ability to examine our art and critique it.

    If we’re lucky, we even get to a point where we know what we don’t know. But the path of knowing more sometimes means we grow away from the positions we held in the past.

    More patient

    Mr. Vestal describes part of the growth process as becoming more patient. With ourselves. I know for myself, I feel less need now to shoot quantities of images. I used to be in a frenzied rush to capture everything that was the least bit interesting. These days I will usually come back with fewer images. I can see something nice and not feel the need to take a picture. Sometimes it is sufficient to just acknowledge it and appreciate it. I would rather have a few images that excite me rather than a whole pile of “OK” pictures.

    I think this also applies to our results and growth as an artist. Have you ever found yourself trying to “force” a great image. I do. Maybe less than I used to. As I grow I am more interested in trying to see more clearly what is there and understand how I perceive it, what I want to do with it. Sometimes it doesn’t come. Rather than be a big frustration, it is an opportunity to try to figure out why.

    Have you ever come upon what would be one of your “standard” images, one you would always shoot, and said, “no, that doesn’t interest me today”? Something is speaking to you to tell you you have grown to a new position.

    Recognize

    To me, the phrase in his quote “less inclined to rush past our own work that we don’t yet recognize” is brilliant. I sometimes run across something while I am looking for a particular image. Something I didn’t think was very good, but for some reason I kept it. Looking at it some time later I liked it much better. Sometimes I realize that if far more representative of my current vision that things I used to shoot.

    He describes them as accidentally good shots. I believe these accidental shots are sometimes our subconscious trying to show us something we don’t recognize yet. As we grow in our artistic concept, we have to leave the past behind. We become bored with what we used to proudly do. Recognize that feeling. Learn from it. It is time to move on.

    I have described before that I tend to be fairly brutal about culling out bad or uninteresting shots. Sometimes, though, I am compelled to keep an image that I don’t think I like. Sometimes I find, later, that this image is significant to me. It may even be a pivot to a new direction in my journey. I did not recognize it at the time, but I did perceive that there was something there that made me keep the image and come back to it later.

    Be receptive

    I believe we should learn to be more receptive to these signals our subconscious is sending us. The subconscious mind is more powerful than the conscious mind. It understands us better. It is not deluded by ego or financial considerations or social media followers.

    I have heard it said that this message from our subconscious is usually not a light bulb going on, it is more like a tickle on the back of our neck. That little feeling that there is something here we are missing or need to figure out. Maturity is learning to be aware of this hint and follow it to see where it leads us.

    How about you? Have you ever puzzled over an image you couldn’t figure out, only to recognize later that it was a harbinger of a new direction for your creative work? The way to a new creative plateau? Did you trust your instincts and embrace the new direction? What was the result?

    I would like to know! Leave a comment or email me.

  • Blessing of Technology

    Blessing of Technology

    I admit to starting to become a Luddite in some ways. I spent a long career developing and working with advanced technology, but I am starting to object to its misuse, especially by giant corporations and the government who spy and track and infringe our rights. But on the other hand, I occasionally step back and look at where technology has taken the art of photography and have to say “wow”. We live in the best of times for digital imaging. Technology can also be a blessing.

    Old books

    I think what precipitated this is that I have been going back re-reading my library of photography books. Many of these are by well-known experts of their day. It has been an amazing realization that many of the images in some of them would not be exceptional or even noticed today. And in some, the author’s discussion of the images was mostly about exposure and technical problems. Exposure used to be an overriding concern. We have come a very long way.

    In particular, I based this on going back over the following books. This is just a fraction of my library that I have looked at recently.

    • The Fine Print, by Fred Picker, 1975
    • Taking Great Photographs, by John Hedgecoe, 1983
    • The Photograph: Composition and Color Design, by Harald Mante, 2010
    • Learning to See Creatively, by Bryan Peterson, 1988
    • Photography of Natural Things, by Freeman Patterson, 1982
    • The Making of Landscape Photographs, by Charlie Waite, 1992

    Film

    Most of these books were based on film photography. It amazes me the degree of technical sophistication and planning that was required. For instance, in The Fine Print, most of the discussion about each image was about the film choice, adjusting the camera tilt/shift settings, exposure considerations, development chemistry, and printing tricks.

    Do you remember reciprocity failure and how to compensate for exposure degradation on long exposures? Do you know exposure chemistries and how to push process a negative to increase contrast? How about dodging and burning during printing? Or making an unsharp mask?

    I skipped this whole generation by shooting slide film during those days. This complex process of color or black & white developing and printing was not for me. And I’m an Engineer. I generally like complexity.

    I would say that many of the results I notice in these old books are “thoughtful”. They have to be. It was generally a slow process. It could take an hour to set up for a shot and determine the exposure and anticipate the printing that would have to be done.

    I am very thankful I was able to skip this. I am able to be much more spontaneous and intuitive in my shooting. My standards have become very different.

    Early digital

    Did you know Kodak invented digital photography? I bet they wish they didn’t. It put them out of business.

    The first prototype in 1975 was an 8 pound monster the size of a toaster. It took 23 seconds to record a blurry black & white image that had to be read by a separate, larger box.

    But unfortunately, for them, Kodak suffered the classic problem of large corporations with entrenched technology: they did not aggressively pursue the new technology for fear of cannibalizing their existing products. They could not convince management that they are going to be cannibalized, and they would be better off doing it themselves. This has put a lot of companies out of business. Who is your buggy whip provider?

    Many years of technology improvements and innovation were required before we got an actual digital camera, the Dycam Model 1 in 1990. The first practical digital camera, in my opinion, was the Nikon N8008s in 1992. It had a whopping 1.5 million pixels and could do color!

    Collecting pixels is not much benefit unless we can do something with them. Adobe Photoshop 1.0 was released in 1990 on the new Macintosh computer from Apple. Hard to believe there was a time before Photoshop. Or Apple 🙂

    Engineering improvements

    As a note on something I have observed over a long career: don’t underestimate the power of engineering. The early digital components were just toys, but they gave a hint of what was possible. Most people dismissed them as impractical, predicting they would never be at parity with film. Now even the most die hard film enthusiasts would be hard pressed to make a good argument that film is better.

    Engineers and scientists and manufacturers and marketers can do amazing things when there is a market to support them.

    An anecdote will illustrate. A friend of mine at HP developed the ink jet printer technology. It was black and white and pretty crude and slow. Not too long after the first one was made, he told me that someday I would take an 8×10 print out of one of these printers, in full color, and it would look every bit as good as a Kodak print. I politely told him he was crazy. But now, here in my studio, I have a 17″x22″ ink jet printer that makes color and black & white prints far better than commercial prints of a few years ago. Much larger printers exist, too. It stretches belief.

    State of the art

    Look at where we are now (mid 2022 when this was written). I shoot a 47MPix mirrorless camera. The lenses have better optical properties than ever before. They support the full resolving power of the camera sensor.

    I can shoot great quality at much higher ISO speeds than has ever been possible.

    This camera has abandoned the optical viewfinder and has gone to a marvelous little video display instead. It shows a wealth of information that photographers in the 1990s and before would never have dreamed of. Or I could chose to see the information on the camera back instead.

    Since the camera is mirrorless, the sensor is live all the time, continually measuring exposure across the entire frame. No more 18% gray reflected light meter to interpret. And this exposure information is real time displayed for me as a live histogram, focus tracking, etc. Whatever I choose to see.

    Exposure is a minor consideration most of the time. I am usually in Aperture Priority mode and the camera’s internal computers do a wonderful job of accurately determining exposure from the data it can see from the whole sensor. Plus I have the histogram to look at to check for abnormal conditions. And the sensor has such an exceptional dynamic range (range of light capture ability from darkest tones, to brightest) that even if I miss the exposure by a stop or 2, I probably have sufficient data to correct it in the computer. Besides, I can immediately review any image to double-check it.

    An embarrassment of riches

    I am almost embarrassed to have all this power at hand. Compared to image making of a few years ago it is like going from Morse Code to an iPhone.

    I don’t worry much about exposure now. I can see what I am about to capture. Even before shooting I know from the histogram that it will be well exposed. I can immediately review any images to verify them. No doubts. No anxiously waiting for the developed film to come back to see if I got the shot.

    This technology frees me from most of the mundane technical concerns and lets me concentrate on composition and creativity. The resolution and tonal detail in my images is the best in history. The computer processing power and tools are the best in history. Printing or display of images has never been better. The ability to transfer even huge files anywhere in the world in seconds is amazing and unprecedented.

    Thank you, technology! It is a golden age of imaging. We have a blessing of technology.

  • Is Scaling Bad?

    Is Scaling Bad?

    I have written about image sharpness before, but I was challenged by a new viewpoint recently. An author I respect made an assertion that gave me pause. He was describing that when you enlarge film it is an optical scaling but digital enlarging requires modifying the information. Implying that modifying information was bad. So I was wondering, is digital scaling bad?

    Edges and detail

    Let me get two things out of the way. When we are discussing scaling we only mean upscaling, that is, enlarging an image. Shrinking or reducing an image size is not a problem for either film or digital.

    The other thing is that the problems from upscaling mostly are edges or fine detailed areas. An edge is a transition from light to dark or dark to light. The more resolution the medium has to keep the abruptness of the transition, the more it looks sharp to us. Areas with gradual tone transitions, like clouds, can be enlarged a lot with little degradation.

    Optical scaling

    As Mr. Freeman points out, enlarging prints from film relies on optical scaling. An enlarger (big camera, used backward) projects the negative on to print paper on a platen. Lenses and height extensions are used to enlarge the projected image to the desired size.

    This is the classic darkroom process that was used for well over 100 years. It still is used by some. It is well proven.

    But is is ideal? The optical zooming process enlarges everything. Edges become stretched and blurred, noise is magnified. It is a near exact magnified image of the original piece of film. Unless it is a contact print of an 8×10 inch or larger negative, it has lost resolution. Walk up close to it and it looks blurry and grainy.

    Digital scaling

    Digital scaling is generally a very different process. Scaling of digital images is usually an intelligent process that does not just multiply the size of everything. It is based on algorithms that look at the spatial frequency of the information – the amount of edges and detail – and scales to preserve that detail.

    For instance, one of the common tools for enlarging images is Photoshop. The Image Size dialog is where this is done. When resample is checked, there are 7 choices of scaling algorithms besides the default “Automatic”. I only use Automatic. From what i can figure out it analyzes the image and decides which of the scaling algorithms is optimal. It works very well.

    All of these operations modify the original pixels. That is common when working with digital images and it is desirable. As a matter of fact, it is one of the advantages of digital. A non-destructive workflow should be followed to allow re-editing later.

    Scaling is normally done as a last step before printing. The file is customized to the final image size, type of print surface, and printer and paper characteristics. So it is typical to do this on a copy of the edited original. In this way the original file is not modified for a particular print size choice.

    Sharpening

    In digital imaging, it is hard to talk about scaling without talking about sharpening. They go together. The original digital image you load into Lightroom (or whatever you use) looks pretty dull. All of the captured data is there, but it doesn’t look like what we remembered, or want. It is similar to the need for extensive darkroom work to print black & white negatives.

    One of the processes in digital photography in general, and after scaling in particular, is sharpening. There are different kinds and degrees of sharpening and several places in the workflow where it is usually applied. It is too complex a subject to talk about here.

    But sharpening deals mainly with the contrast around edges. An edge is a sharp increase in contrast. The algorithms increase the contrast where an edge is detected.

    This changes the pixels. It’s not like painting out somebody you don’t want in the frame, but it is a change.

    By the way, one of the standard sharpening techniques is called Unsharp Mask. It is mind-bending, because it is a way of sharpening an image by blurring it. Non-intuitive. But the point here is this is digital mimicry of a well known technique used by film printers. So the old film masters used the same type of processing tricks to achieve the results they wanted. They even spotted and retouched their negatives.

    Modifying pixels

    Let me briefly hit on what I think is the basic stumbling block at the bottom of this. Some people have it in their head that there is something wrong or non-artistic about modifying pixels. That is a straw man. It’s as silly as saying you’re not a good oil painter if you mix your colors, since they are no longer the pure colors that came out of the tubes. I have mentioned before that great prints of film images are often very different from the original frame. Does that make them less than genuine?

    Art is about achieving the result you want to present to your viewers. How you get there shouldn’t matter much, and any argument of “purity” is strictly a figment of the objector’s imagination.

    One of the great benefits of digital imaging is the incredible malleability of the digital data. It can be processed in ways the film masters could only dream of. We as artists need to use this capability to achieve our vision and bring our creativity to the end product.

    I am glad I live in an era of digital imaging. I freely modify pixels in any way that seems appropriate to me.

  • Black & White – in Color

    Black & White – in Color

    What? Isn’t that contradictory? Isn’t black & white is about the absence of color? I wanted to follow up on a previous article on how we get color information in our digital cameras with a nod to the purity of black and white and emphasize how it is still dependent on color.

    Remove the color filter?

    I indicated before that our sensors are panchromatic – they respond to the full range of visible light. If we want black & white images, shouldn’t we just take the color filter array off and let each photo site respond to just the grey values?

    We could, but most black & white photographers would not be happy with the results. It would be like shooting black & white film. A problem with black and white film is that it eliminates all the information that comes from color. Through interpolation of the Bayer data, we get full data for red, green and blue at each pixel position. If we removed the filter array, we would have only luminosity data. So before even starting, we would be throwing away 2/3 of the data available in our image.

    At that point we would have to resort to placing colored filters over the lens, like black & white shooters of old had to do. They did this to “push” the tonal separation in certain directions for the results they wanted. But this filter is global. It affects the whole image rather than being able to do it selectively as we can with digital processing. And it is an irreversible decision we would have to make while we were shooting. Why go backward?

    What makes a good b&w image?

    Black & white images are a very large and important sub-genre of photography. The styles and results cover a huge range. But I will generalize and say that typically the artists want to achieve a full range of black to white tones in each image with good separation. Think Ansel Adams prints.

    Tones refer to the shades of grey in the resulting print. We do a lot of work to selectively control how these tones relate to each other. Typically we want rich black with a little detail preserved in them, bright whites, also containing a little detail, and a full range of distinct tones in between. These mid-range tones give us all the detail and shading.

    Tone separation

    If one of the goals of black & white photographers is to have high control of the tones, how do we do that? Typically by using the color information. I mentioned putting colored filters over the lens. This was the “way back” solution.

    Landscape photographers like Ansel Adams often used a dark red filter to help get the deep toned skies they were known for. Red blocks blue light, forcing all the blue tones toward black.

    Digital processing gives us far more control and selectivity than the film photographers had. We don’t have to put the filter over the whole lens and try to envision what the result will be. We can wait and do it on our computer where we have more control, immediate previews, and undo. But all this control would be impossible without having a full color image to work with. As a matter of fact, modern b&w processing starts by working on the color image. Initial tone and range corrections are done in color. Good color makes good b&w.

    B&W conversion

    Obviously, at some point the color image has to be “mapped” to b&w. This is called b&w conversion. It can be a complicated process. There are many ways to go about the conversion, and each artist has their own favorites. There is no one size fits all.

    It is possible to just desaturate the image. This uses a fairly dumb algorithm to just remove the color. It is fast and easy, but it is usually about the worst way to make a good b&w image.

    You could use the channels as a source of the conversion. The RGB colors are composed of red, green and blue channels. These can be viewed and manipulated directly in Photoshop. They can often be useful for isolating certain colors to work on. Isolating the red channel would be like putting a strong red filter over the lens.

    Lightroom and Photoshop have built in b&w conversion tools. In LIghtroom, choose the Black & White treatment in the Basic panel of the Develop module. This has an interesting optional set of “treatments” to choose from in the grid control right under it. In Photoshop use the B&W adjustment layer.

    Both of these have the power of allowing color-selective adjustments. This is huge. Tonal relationships can be controlled to a much greater degree than was possible with film. If we want to just make what were the yellow colors brighter, we can do that. Of course, Photoshop allows using multiple layers with masking to exert even more control.

    There are many other techniques, such as channel mixing or gradient maps or plug-ins like Silver Effects to give different and added control. It is actually an embarrassment of riches. This is a great time to be a b&w photographer.

    It starts with color

    What is common to all of this, though, is that it starts from the color information. Color is key to making most great black & white images.

    I sometimes hear a photographer say “that image doesn’t work well in color, convert it to b&w”. Sometimes that works, but I believe it is a bad attitude. B&w is not a means of salvaging mediocre color images. We should select images with a rich spread of tones, great graphic forms, and good color information allowing pleasing tonal separation. Black & white is its own special medium. Remember, though, usually it requires color to work.

  • What the Camera Sees

    What the Camera Sees

    One of the important things every photographer has to learn is to see what the camera sees. It is a different process from painting or other visual art. It is a technical process, not only of how the sensor works but the transform of a 3 dimensional world to a 2 dimensional representation. This is part of our art. We have to understand it and be able to predict the results.

    Static image

    Unless you are shooting video, the end result of the camera’s capture is a static image. That seems like a “duh” to most of us, but it is significant. The entire image is recorded “in one instant”. Yes, I’m ignoring moving shutter slit, HDR, panoramas, time exposures, and other exceptions that can bend the rules.

    This “in one instant” is significant because our eyes work in a totally different way. We can only see a small spot at a time. We continually “scan” around a scene to “see” it all. Our brain stitches all these scans together marvelously to give us the impression of a complete scene. We are not aware of it happening.

    What difference does it make? Well, there are subtleties. If something moves in real life, our eyes jump to the movement and study it. Movement has a higher priority in our brains than static things.

    Our photograph no longer has that movement or flashing lights. It is a flat and static collection of pixels. We have to learn techniques to stimulate the viewer’s eye in other ways. We learn that the eye is drawn to the brightest or highest contrast areas. That informs how to capture the scene and process it to end up with results that help direct our viewer to the parts of the image we want to emphasize. It helps a lot to anticipate what we are going to want to do. This is part of learning how the camera sees.

    Depth of field

    The static image we create may or may not seem in sharp focus throughout. This is known as depth of field. It is referring to which parts of the scene are in “acceptable” focus. The aperture setting controls the range of this good focus area.

    Remember that the 3 main things controlling the exposure of an image are the aperture, the shutter speed, and the ISO setting. The aperture controls the amount of light coming through the lens at any instant. How long the sensor is exposed to the light is the shutter speed. And the ISO setting is the sensitivity of the sensor to the light. A side effect of the aperture setting is the control of effective depth of field.

    In real life we do not see limited depth of field. Our eyes focus on one small area at a time. Each spot we focus on is in sharp focus. The resulting image our brain paints is that everything is in focus. Try it. Look around where you are now. Then close your eyes and try to remember which parts were out of focus. Spoiler – there aren’t any. We remember it all in focus.

    So this is a big disconnect between what we perceive of a live scene and what we record in a photograph. Some photographers see this as a problem if they cannot keep the entire scene in sharp focus. But intentionally making non-subject areas blurry can also be used for artistic effect. Since this is different from how our eyes see, this creates something that stands out. It can change our perception.

    But like it or not, it is something that the camera sees differently and we need to learn how to handle it.

    Shutter speed

    To our eyes, things seem to be either frozen sharply or “just a blur” moving by. Things are usually only perceived as a blur if we are not paying attention to them.

    But for the camera, the shutter is open for a certain amount of time and things are either sharp if they are still or blurred if they are moving. The camera does not understand the scene and it is not smart enough to know what should be sharp.

    Let me give an example. Say you are standing beside a road watching a car go by. If we care about the car (wow, a new ______; that would be fun to drive) we are paying attention to it and we perceive it as sharp. To the camera, it is just something moving through the frame while the shutter is open. It has no name or value. The photographer has to determine how to treat this motion. What it should “mean”.

    So the photographer may pan with the car to make it appear sharp while the rest of the image is blurred. Or the intent might be for the car to be a blurred streak in the frame. Either way, it is a design decision to be made because the camera records movement differently from us.

    The lens

    Unlike us, our cameras let us swap out a variety of “eyeballs” – the lens. We have a certain fixed field of view. That is why camera formats have a particular focal length designated as the “normal” lens. For a full frame 35mm camera like I use, the “normal” lens is in the range of 45-50mm, because for this size sensor this corresponds to the field of view we typically see.

    But most of our cameras are not limited to that. We can use very wide angle lenses to take in a larger sweep of scene. Or we can use a telephoto lens to bring distant subjects close or to restrict our view to a narrow slice. Or we can use macro lenses to magnify small objects. All these things give us a new perspective on the world that would not be possible with our regular eyes. This is another way the camera sees that we need to learn to use.

    Mapping to 2D

    The world is 3D. Pictures are 2D. It seems obvious. Yet we must be aware of the transformation that is happening.

    In the 3D space we move in, we are acutely aware of depth and movement in many axes – length, width, height, pitch, roll, yaw, and others. We use this information automatically to interpret the world. But it is lost when the scene is captured on our 2D sensor.

    We sense depth. “In front of” or “behind” come automatically to us. Our camera is not as smart. The camera sensor records everything in front of it as a flat, static image. The scene is mapped through the particular perspective of the lens being used and onto the flat sensor.

    An example to illustrate. This is a classic. You take a picture of your family downtown. The scene looks perfectly fine and normal to you, because you intuitively realize the depth and separation of things. It gives you selective attention. But when you look at the picture there is a very objectionable telephone pole poking out of Uncle Bob’s head. You did not pay attention to that at the time because you “knew” the pole was far behind him and you dismissed it. The camera doesn’t know to ignore it. All pixels are equal.

    Light

    This is fundamental to our cameras. There has to be a light source. The camera sees only light from a source or light that is reflected or transmitted by objects. But being humans, we interpret the real world as objects. They are “there”. They have mass and form and value and color. Not so to the camera. It doesn’t ascribe meaning to a scene. All a camera can record is light. Our fancy sensor doesn’t see a red ball. It detects, but doesn’t care, that there is a preponderance of light in the red band being recorded.

    By its very definition – photo-graphy means writing with light – photography is dependent on light. Our modern sensors are marvelous products. We can shoot at very high ISO and make exposures in almost total darkness. But if any image was recorded, there was some actual light available.

    Everything in every image we make is a record of light. More than almost any other art form, photography is dependent on light. Photographers must be intensely sensitive to the direction and quality and color of the light sources that are illuminating our scene. Likewise we must be very aware of the objects the light is falling on, their shape and texture and reflectivity and color.

    Learning to see, again

    Art in general, and photography in particular, is a lifelong learning. We learn to see creatively. We learn to see compositions and design. And we have to learn to see the way the camera sees. This is the way we capture the image we want.

    Note, after writing this I found this good article by David duChemin. He is a great writer.