Originally Posted by
Manfred M
A few problems with your suggestion John.
Assuming that your subject is properly lit (18% gray), the background needs to meter at least 4-1/2 stops more to get a black background. If you meter the subject to properly expose at f/8 (using a reflective meter), then the background needs meter at around f/1.5. It does not matter how one achieves this; a combination of colour of the material or just managing the light.
In a daylight situation, controlling light drop-off is difficult to impossible. There has to be enough light to illuminate the subject and that usually means the same amount of light is hitting the background. That is why we tend to use artificial light; the inverse square law is our friend; at ~ 5x the distance from the light source to subject, even a white background will appear black.. We can do this with any artificial light source, but the reason we tend to use flash, is that the light is a lot brighter and we can freeze the subject (like the dog and chick).
The other trick is to use Photoshop (not Lightroom) to select the subject and then darken the background to the desired level. This generally means starting with a dark background as light reflecting back from the background to the subject can be problematic.
The reason I use the technique I do, is that it is the most effective, with the least amount of work.