Myths and legends abound in the world of photography. Every so often, I come across one being propounded by a lecturer or instructor. I like to experiment to prove or refute the legend. I am not a professional researcher and do not have the time and tools to draw definitive conclusions, but I offer my results in the hopes that others will confirm or disprove my findings.
Our first "myth" concerns the use of a lens shade. Not so long ago, I heard a lecture in which the presenter recommended never to use one, because it cuts down on the light reaching the sensor.
This seems to be literally true. According to our experiments, removing the lens shade increases the light hitting the sensor by up to 1/3 stop. This is a small difference and occurred in only 1/2 of our samples. The question is whether the quality of the additional light recorded by the sensor enhances the image. Our hypothesis is that the additional light hitting the front element of the lens and reaching the sensor is not part of the intended image and therefore tends to reduce the quality and saturation of the image.
We took two sets of photographs under varying conditions: One was a close-up (macro) of a small flower with a yellow center, white petals and green stem. The other was of a tree in full leaf. In both cases, we took photographs in bright sun and in obscured or overcast sun, with a lens shade and without, and with a polarizing filter and without.
These photos were taken at ISO 100 and f/11 with aperture priority. Using matrix metering, we compared the camera’s metering assessment (in terms of shutter speed) and the histograms of the resulting images.
For each photograph, we also selected 3x3 pixel samples of several areas. For the flower, we sampled the yellow center, the white petals and the green stem. For the, we sampled leaves in full exposure to the light, in partial shade and in deep shade. For each photograph and for each sample, we used the Photoshop Color Sampler Tool, which gave us the RGB values for each sample. From these, we used the Color Picker to calculate the saturation from the RGB values.
In several cases, the shutter speed selected by the camera’s light meter for the photograph taken without a lens shade was shorter, by no more than 1/3 stop. But the photographs taken with the lens shade showed a few percentage points greater saturation than those taken without it.
The myth is questionable. You may see a small increase in the amount of light recorded by your sensor (or be able to use a faster shutter or small aperture) if you do not use a lens shade. But the increase in light will not improve your photograph. The additional light will be extraneous and tend to reduce the saturation of your image. After all, reducing extraneous light is what the lens shade is for in the first place!