Airport Morning

Airports, to me at least, tend to be very technical looking. There is nothing wrong with this, I can find incredible beauty in these man-made constructs.

But I was delighted when I saw this sunrise over the airport one morning:

Airport Morning

I love the luminous quality of the sky and the way the dramatic clouds are making way for the blue sky (or is it the other way around?). The ground mist softens up the shapes of buildings, airplanes, and other artifacts of man just enough to make it clear that everything is part of nature, whether we realize it or not.

Stormy Landscape

I'm a bit behind with my photos, so here is another one from the fall:

Stormy Landscape

We were visiting friends and as I looked out the window, the incredible light in the storm clouds caught my attention. Fortunately, my friends know me and did not comment when I grabbed my camera and ran to the door.

A few hundred meters further lay some fields, which made a wonderful counterweight to the clouds in the sky. While I was still standing and thinking about the composition, the sun broke through the clouds and shone on the grass below. In that moment, everything came together and I simply pressed the shutter release.

Autumn Foliage

Autumn has been around for a few weeks now, and for the last two weeks or so, we've had some pretty fantastic light, especially in the morning. And for the last two weeks or so, I have either been unable to shoot at all or the images did not turn out the way I wanted them.

You can image my delight when, this weekend, I finally got everything just right ...

This one was taken very early:

Autumn Road

and this one later, when the sun was already up a bit, but still mostly behind clouds:

Autumn Treescape

Both are the same row of trees, jut very different perspectives.

[Linux] Xfec crashes after login

Disclaimer: This off-topic post is about a solution to a problem that you will only have if you use Linux. If you are of the Mac or Windows persuasion, you're free to look at some cool photos of mine, because this is definitely not your problem. :)

If you log in and then Xfec (or Gnome) crashes before the desktop is visible, and you can't read the error message that briefly appears on a console screen, you are probably seeing the bug I saw today.
Try this:

1. Start a terminal session so you can log in. You do this by pressing  <1> in the login screen. Then log in. To get back to the graphical screen, press <8>.
2. After logging in, you will be in your home directory. Check if the file .ICEauthority is readable by you:
   $ cat .ICEauthority
3. You should get an error message. If you do not, you have a different problem and I won't solve it (at least not in this post ;-).
4. If you did get an error message, delete the file and re-create it:
   $ rm .ICEauthority
   $ touch .ICEauthority
5. If you log in now using the graphical login screen, xfce (or Gnome) should start up just fine.

Enjoy using Linux!

Water Lily

The water lily (a.k.a Nympahea) in the image below was in a pond in a public garden. It was evening (we actually made it out just as they where locking up) and rapidly getting dark. I did not have a flash ready, so I shot a few frames as ISO 800, meaning to capture the wonderful dark pink color of the petals and the rich dark yellow of the stamina against the reflections of the dark water.

It turns out that I dislike the noise in the color image to the point of finding it objectionable. Noise reduction did not really work for me, because it removed all the texture from the petals due to smoothing. Before tossing the image, I decided to try it in black and white (thanks, Lenswork, for reminding me that black and white is not dead! But that's for another post.)

In black and white, I like the slightly gritty texture on the petals that is caused by the noise.

Water Lily

What is, unfortunately, not visible here is the huge number of tiny drops on the petals. You can
see some of them (as splotches) on the petal in the 9 o'clock position, but there is a huge number of them on most of the petals. Either they are too small to be seen at this size, or my skill is insufficient to make them visible at this resolution - they are definitely there in the full image.

Does anyone want to purchase a print? ;-)

Image Clarity 101: Depth-of-Field

In the last post, we looked at how a sharp image is created optically. In this post, we will look at how the physics render non-flat objects.

If all the points of the subject are in the same plane, they will all render with the same size circle of confusion in the image plane. This is the case if the subject is perfectly flat.

For non-flat subjects, the points of the subject are located at different distances from the image plane. So the projected points will have a minimal circle of confusion in different image planes. Since there is only one image plane, the projected points will all have different size circles of confusion - which means they will all be of different sharpness.

Each circle of confusion that is small enough will appear to be sharp. The distance from the nearest to the furthest point which are just rendered sharply is the depth of field.

The depth of field is determined by the distance of the subject from the camera, the focal length of the lens, and the aperture.

Some simple rules of thumb are:

1.  The further the subject from the lens, the greater the depth of field for a given focal length.

The greater the absolute distance between subject and lens, the smaller the relative difference in distances for different points of the subject. Because of this, the size of the circles of confusion are very similar in size.

If you look at the distance scale on a lens, you will notice that the distance between markings decreases the closer you get to infinity. And, speaking of infinity, there is a point from which on everything is in focus if you focus the lens to infinity.

2. The shorter the focal length, the greater the apparent depth of field at a given distance.

The hyperfocal distance, or the distance from the image plane past which every subject point is acceptably sharp if the lens is focused on infinity, decreases the shorter the focal length of the lens. This is because the magnification decreases, so the circle of confusion for a given subject point is also magnified less.

Remember though, that this is true only for a fixed distance!

3. The smaller the aperture, the greater the depth of field.

The smaller the aperture, the smaller the cone of light rays that passes to the image plane. Because the cone is smaller, the circle of confusion is also smaller.

In the illustration below, the aperture blocks the blue cone of light rays, only the red cone gets through. The circle of confusion on the image plane is smaller, so the image is sharper.

Illustration 3: A smaller aperture reduces the circle of confusion

Note that in practice, diffraction becomes a problem at small apertures. Diffraction will be discussed later in this series.

Bigger is not better

One important thing to keep in mind is that bigger is not necessarily better with depth of field. An image may actually be improved if (unimportant) parts are kept out of focus because the eye tends to focus (pun intended) on the part of the image which are sharp and tends to give the unsharp parts only cursory attention.

That said, if you are trying to render your image as clearly (sharp) as possible, you want to select your depth of field in such a way that the closest and furthest subject point which you want sharp are in focus.

For example, have a look at this image:

Image 1: The forget-me-not in the foreground is sharp, the background blurred.

The forget-me-not flower in the foreground is rendered in focus. The (rather cluttered) background is rendered out of focus.  The eye of the beholder will pass over the out of focus parts, thereby de-emphasizing the non-essential parts and concentrate on the subject in the foreground.

Image Clarity 101: What makes an image sharp?

A common problem with photos is lack of sharpness. The image is either soft, or out of focus, or the wrong part of the image is in focus, or ... the list of possible issues is a long one.

Just like exposure, focus is one of the parameters that the photographer must learn to control in order to create images that show what he or she visualized before pressing the shutter release.

This is the first of a series of posts that I will call "Image Clarity 101". The name is a tip of the hat to John B. Williams who wrote the excellent "Image Clarity: High-Resolution Photography", which - alas - seems to be out of print.

I am going to look at what causes an image to be "sharp". In later postings, I will explain what equipment and techniques to use to actually get an image to be "sharp".

Focus

If we imagine that a subject is made up of an infinite number of minuscule points, each of these points emits an infinite number of light rays that hit the entire area of the camera lens. As the light rays pass through the lens, they are focussed on some point (the focal point) behind the lens, creating a cone of light.

Parallel to the lens plane is the focal plane, which holds an infinite number of focal points for all the visible points of the subject.

All of this is shown in the illustration below.

Illustration 1: Focus Explained (simplified)

The image plane is the surface the image is projected onto. This is where the film or image sensor is located. For an image to be in focus, the image plane must be the focal plane.

When you twist the focus ring on a lens, you are effectively moving the focal plane. When the image is sharp, the focal plane is located on the image plane.

Are you with me so far? Good!

Circle of Confusion

Now it gets a bit messier: since we are dealing with the real world, the light rays do not actually all converge on a single point, but form a small area, the circle of confusion. 

In the illustration above, you can see that in the focal plane most of the light originating from a single point of the subject hits the small circle. As the image plane moves away from the focal plane, the light is spread over a larger area.

If this is too circle of confusion business to too confusing, have a look at the following, simplified illustration:

Illustration 2: Cone of Light

The subject is projected by the lens as a cone of light rays which strike the image plane. The tighter the cone is at the image plane, the close the image plane is to the focal plane.

If the circle of confusion is small enough, the human eye will register it as a single point. How small the circle needs to be is perhaps a topic for another post. For the time being, we can assume that if the circle of confusion is somewhat smaller than a single photo site on the sensor, it will not be a limiting factor for the overall sharpness of the image.

Illustration 3: As the circle of confusion increases, the image becomes less sharp.

So we reach a simple conclusion:

If a single point of the subject is rendered as a small enough circle of confusion, it will appear sharp in the image.


There is one important point to consider: all of what has been discussed above is only true for flat subjects and ideal lenses. In the next installment, we will look at sharpness for a non-flat subject.

You may find a used copy of the excellent Image Clarity here:
Amazon USA Amazon UK Amazon DE

If you don't feel like getting an old book, you might try perusing the good old Wikipedia which contains much more on the subject.