Subject contrast and exposure range

You are here: Nature Science Photography – Contrast – Contrast and exposure

What conclusions can we draw up to this point for the oh-so-necessary exposure metering? Some books almost mystify this process, but we can simplify it within the context of our consideration.

Consequence number one: Without a comparison between the contrast of the subject and the ability of the image carrier to reproduce it (the permissible exposure range), exposure metering is of little use. Only after understanding their relationship can we determine exposure. We remember: On the density curve of each image carrier, we find two threshold values. One is the minimum amount of light needed to create an image. The other represents the maximum light level beyond which a stronger exposure no longer results in stronger blackening. The wider the largely linear range of the density curve, the more contrast we can accommodate in an exposure. If the subject contrast and the permissible exposure range correspond, the only correct exposure value must be determined. If, on the other hand, the subject contrast is smaller than the permissible exposure range, there is a real exposure latitude, and we may consider more than one single exposure value as correct. But, and this is often the case, if the subject contrast is greater than the permissible exposure range, we cannot correctly expose the image without intervention.

In practice, we first determine the subject’s contrast. A spot meter is the most suitable tool for this because it enables us to precisely measure even smaller parts of the subject. We use it to measure the exposure for those highlight and shadow details in which we really want to be able to recognize structure and details in the image. Drop shadows, light reflections or small light sources may be passed over with a clear conscience since they will not dominate the image as a rule.
Figure
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(Contrast and metetring)

shows practically which criteria should be taken into account. The selection of the measuring point in the highlights aligns with the number 1, as there is still a discernible trace of structure in this cloud area. Further down, in the part of the sky marked with 3, on the other hand, any detail is missing, so it can be safely disregarded. For the shadows, the area of the rock face labeled number 2 was chosen. The opposite large shadow area number 4 is even darker, but according to my image conception, it should „drown“ to the black silhouette and thus set a visual counterweight. – Notice what? Image expression and image composition also play a role in exposure finding. If you don’t have an external spot meter or your camera doesn’t have a TTL spot meter, you can assist yourself by setting the relevant part of the subject with the zoom lens to almost fill the format with integral metering, and then reading off the aperture values at the same exposure time in each case (or conversely, the exposure time at the same aperture value in each case, whichever you prefer). The subject contrast then corresponds to the difference in brightness between the two measuring points, and ideally, it precisely fills the exposure range of the image carrier. This scenario is convenient, as previously mentioned, as it allows us to proceed directly to the actual exposure measurement without any intermediate steps.

Next 12% or 18% – The problem of the calibration value of the exposure meters

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