Just photograph a rose and show its beauty – how wonderful that would be. Is the light right ? Do false shadows emerge ? Is the structure correctly reproduced ?
Again and again I have to go through our garden and look at the flowers. Yesterday was it again. The sun had just set and the full moon should have decreased a little later.
I tried it with all f-stops the camera and lens gave to me. To my surprise the aperture 32 at ISO 50 with 45s exposure speed was my favorite. Only at the edge the picture had to be darkened and desaturated. Post-processing can be as simple as that.
Recovering from a strenuous afternoon where I was exposed to an increasingly deep dementia I sat in my hotel to have a light meal. Nerve-racking music all over the room. A beautiful sunset with warm colors and flattering light after a grey and rainy day.
Dementia shows a person deprived of many intellectual capabilities. There is still the capability of a relation left, weak and vulnerable. There is no understanding left for us. Speechlessness counts the most.
I assume that everyone has had at some point the experience where less was more. Especially when dealing with computer based image postproduction. Software makes handy wonderful, or better: powerful, filters. Experienced artists know that only a pinch of something or homeopathy is a key to better results.
The same holds true in X-ray production. A maximum of energy does not provide better images. Let’s look closer at this point.
What is the influence of energy to X-ray images ?
Higher energies in X-rays mean shorter wavelengths and a higher resolution. Therefore it might seem reasonable to increase the energy in our X-ray tubes always to the maximum to produce incredible images based on a maximum resolution.
With four images below I show the influence of increased energy levels on X-ray images of a single rose. The applied energy levels are 40kV, 60kV, 90kV and 109kV. The steps of postproduction were the same in every image. Slight differences are owed to best contrast in each exposure.
Surprisingly to the novice we get an increasing loss of contrast (or less available contrast) in each image with higher energies. This effect of loosing contrast can easily be seen in this series of four X-rays and is highest at 109kV.
The explanation for less available contrast with higher energies is the following physical effect: the more photons have shorter wavelengths the more photons run unaffected through the object down onto the sensor. With all photons running through without any hindrance the sensor would show a homogenous gray value.
Every structure looses contrast when turning to higher energies. The optimum for a structure is found by experience and varies significantly.
In the medical field the applied energy strongly depends on the purpose of the examination and the structural demands to be diagnosed.
The above demonstrated meaningless low contrast for our single rose at 109kV doesn’t hold true at all in radiology. Radiologists use frequently 125kV for a chest film to get reproducibly valuable contrast in most patients.