Rain, Uniform Light, UV Filters

You are here: Nature Science Photography – Lightness and color – Color saturation

Even though there is usually not much positive to be gained from a downpour, in the vast majority of cases it makes for darker, more saturated colors. This is not because the water changes the colorants, but because the thin film of moisture smoothes the surfaces. The fine pores are closed so that the incident light can also no longer be reflected off them. Instead, a larger part of the spectrum corresponding to the inherent color is absorbed, which reduces (makes darker) and intensifies the reflected part.

An old but still useful piece of advice is to shoot macro studies and still lifes in particular under the uniform reflected lighting of an overcast sky. This is because the dense cloud cover finely distributes the light and, since it comes from all directions, reduces the proportion of angles that are particularly critical for surface reflections, which can now no longer permanently reduce color saturation. In addition, the diffuse lighting reduces the harsh cast shadows and thus levels the contrast.

Discussing the sense and nonsense of UV filters is for some photographers about the same as bringing up the topic of Chevy vs. Ford in the USA – I know, I know. Nevertheless, let’s briefly recapitulate the facts in the context of our consideration here. From the range of spectral sensitivity of the recording material between about 370 and 700 nm, we can see that most photographic films are also sensitive to ultraviolet (UV) radiation, which is invisible to us. Science defines UV radiation as the region of the spectrum between 100 and 400 nm and divides it as follows:

UV range Wavelength in nm		   Absorbance in the ozone layer
UV-A 320 - 400 (long-wave) 		   barely
UV-B 280 - 320 (short-wave) 		   90 percent
UV-C 100 - 280 (extremely short-wave) 	   100 percent

The intensity of UV radiation depends on a) the angle of incidence of the sun, which changes with the time of day, the seasons and the latitude (the northern hemisphere receives more direct sunlight during the northern summer and therefore the UV content is greater), b) the degree of cloud cover, c) the ozone content in the atmosphere, d) the atmospheric opacity, and last but not least, e) the altitude. For humans, excessive exposure to UV radiation can lead to skin tanning or burning due to its high energy content. On the other hand, with film it causes a slight blurring because the optics are best corrected for the visible range of the spectrum, and the imaging error increases the further away the wavelength range is from it. It also causes a slight blue cast because it exposes the layer more strongly to this spectral range. This color cast is particularly noticeable on slide material because it cannot be filtered out there as in negative or digital photography. Film manufacturers prevent these negative effects with special filter layers, and most contemporary lenses also take them into account with elaborate lens coatings. This is sufficient for average altitudes in the country’s interior. In the high mountains and on the coast, however, the intensity of UV radiation increases beyond this normal level. In the first case, the poorer filtering performance of the atmosphere due to the thinner ozone layer is the cause; in the second case, it is isscattered radiation from the water surface. This is precisely where opinions diverge, as many photographers fail to discern any significant difference between photos taken with and without an additional UV filter in such situations. Personally, after many comparisons, I am of the opinion that the cases described suggest the use of a UV filter not only because it protects the front lens of the optics in any case, but because its thicker glass surface and special coating can simply absorb more radiation. Anyway, try it out for yourself. This will give you the only right answer for your equipment and your shooting material. However, you should closely study the data sheet before making the purchase, as some manufacturers solely rely on each glass’s ability to filter out UV radiation between 200 and about 350 nm. – Protected by a window; after all, you don’t get sunburned. However, only a filter capable of blocking wavelengths up to 400 nm can effectively eliminate the wavelengths relevant to film, thereby reducing the portion of the spectrum that contains the highest proportion of scattered violet. Typical representatives of this high-caliber class are the B+W UV 010 or the filters of the Kodak Wratten series with the designations 2A, 2B, 2C, whose extraordinarily high degree of UV blocking is necessary at altitudes of more than 2,500 meters. By the way, polarizing filters are not very effective against UV radiation, so in a shooting situation that requires both, it is advisable to use a combined polarizing + UV filter. By the way, digital technology has an advantage in this case because the silicon chips used for image acquisition are by nature relatively insensitive to wavelengths below 400 nm.

Main Lightness and Color

Previous Polarizing filters

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