Ransom, Love

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Just as the Son of Man did not come to be served, but to serve, and to give his life as a ransom for many.

Matt 20:28

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Love the Lord your God with all your heart and with all your soul and with all your mind. This is the first and greatest commandment. And the second is like it: Love your neighbour as yourself. All the Law and the Prophets hang on these two commandments.

Matt 22:37-40.

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ISO, depth of field

The role of aperture size is extremely important in determining depth of field. There are several factors which in turn determine how wide you can open your aperture and thus, how short you can make the focal length for the lens you are using.

One major factor is the quality of lens, but for now we'll assume that you have to work with whatever you have on the camera at the time. There is a caveat: if you have a zoom lens, then you can adjust the focal length by zooming in and out, and as you do so, the maximum available aperture size may change (if your zoom lens has variable apertures). To simplify things for now, let's assume your zoom lens has a fixed maximum aperture, or you keep the focal length and zoom fixed. Simpler still, let's assume you have a prime lens attached.

The amount of ambient light available to you is another factor in setting your aperture value. Under bright conditions you may not be able to open your aperture all the way because the fastest shutter speed may still result in overexposed images. At the other end of the spectrum, in low light conditions, you still need enough light to allow a fast enough shutter speed to prevent camera shake. One way around this is to steady the camera somehow (tripod, bean bag, resting on a stable surface etc.) and use a shutter release.

The factor I'll discuss now is the ISO setting. In film photography, ISO refers to the light sensitivity of a particular film. In digital photography you can set an ISO equivalent, which is the light sensitivity of your camera's sensor. Higher values are more sensitive to light (and are thus recommended for low light conditions, freezing movement, wide depth of field etc.) Lower values are less sensitive to light and thus require either a slower shutter speed or larger aperture (or a combination of both) to get an equivalent exposure.

In the following example I used three different ISO settings for the same composition and I tried to vary the aperture between wide open or closed down. Each time I used the camera's center-weighted average metering to get similar exposures.

If you look at the camera settings within a column, as ISO increases the aperture value available to me changed. With a more light sensitive ISO (e.g. 800) I had to have the shutter speed set to it's maximum and I still had to close down the aperture to prevent over exposure. At the smallest aperture (right column), increasing ISO required that I increase shutter speed.

The take home message is that for these light conditions, a lower ISO allowed me to use a larger aperture, which shortened the focal length and created a shallower depth of field. It also resulted in slightly more saturated colors (note for instance the saturation of the blue sky as you go down each column).

Depth of field & blossoms

In trying to capture some of the essence of Spring, blossoms and flowers quickly come to mind. This is a brief illustration of some concepts to consider when trying to photograph flowers. This is by no means a comprehensive treatment, but it will hopefully illustrate some of the basics of depth of field which is an important concept for a number of photography subjects.

There are many ways of portraying flowers or blossoms. I use "portray" intentionally since you could think of flower photography as a form of portraiture. One of the ways I like to portray them is to try to isolate them from much of the background noise. You can do so artificially by removing the bloom from its natural context (i.e. pick it and move it to a less cluttered background). This is method that I don't personally condone. Another method is to use an artificial background such as a plain (often dark-coloured) piece of cardboard which you can place behind the subject. While this does place the emphasis entirely on the flower and can produce some astounding results, some may consider this contrived. It really depends on what your objectives are when you set out to create the shot (and on how much of a purist you are).

The method that I tend to prefer is to use a shallow depth of field to highlight the subject and obscure the background. This has an added benefit of retaining some contextual information. To obtain the shallow depth of field you want to have your aperture wide open (i.e. your f-number value usually needs to be small). For instance, f-numbers are denoted by f/1.8, f/22 etc and they represent the ratio of the focal length (f) to the diameter of the aperture (D) or f/D. Having a short focal length relative to the aperture diameter will result in the object at the focal length being in focus and the objects in the foreground or background being out of focus.

However, you need to balance the aperture size with the shutter speed in order to obtain an appropriate or desired exposure. If you are going to have your aperture wide open, this generally means that you need to shoot under fairly low light conditions and/or have a very fast shutter speed. Note that a fast shutter speed is usually a fraction of a second. Many cameras will depict this simply as the denominator i.e. for 1/30, the camera will simply use 30.

An added benefit of shooting under lower light conditions is that the colours may appear more saturated than when under direct sunlight or the harsher light of midday. Unfortunately, when shooting under low light you may have to use a slow shutter speed even with your aperture wide open. Depending on various factors such as the lens focal length and quality and the amount of ambient light, this may necessitate using a tripod to prevent camera shake.

Below is an illustration of some of these concepts. Both photos were taken with the same camera and 50mm lens and from approximately the same vantage point (hand held), but the first was taken first thing in the morning while the second was taken mid morning (these particular blossoms were near the trunk of the tree and were shaded by branches and other blossoms, but the tree was in direct and harsh sunlight).

The aperture value or f-number for the first photo was f/1.8 with a shutter speed of 1/400. For the second photo I used f/22 and 1/80, respectively.