The area within the red square is show below at various apertures and focus stacked.
In jewelry photography, most of the time we need to make sure everything is pin sharp. Having some blurred stones or portions is often frowned upon unless it’s quite deliberately done and for an artistic purpose.
I sometimes receive less than ideal jewelry items to retouch where the focus is extremely limited, or everything is soft as though Vaseline was smudged over the picture. In most cases, the lens and camera are perfectly fine, but the user has done some serious mistakes with how his camera’s setting have been adjusted.
As many of you know, stopping-down a lens, or in human-like analogy, squinting your eyes when you want to see “sharper”, gives you more depth-of-field (DoF). For example, a lens shooting at f2.8, which is quite open, means the lens’ iris is nearly wide open, letting in lots of light – the image will have a very shallow DoF. Therefore to compensate, we stop-down the lens, going from f2.8 to say f5.6, f8, f11… etc.
What I want to cover today is that many of you out there are somewhat unaware of the limits of stopping-down a lens. After a certain point, every lens starts to loose overall sharpness, to the point of looking blurry. Every lens out there suffers this, it’s called “diffraction”.
To explain this, the edges of the diaphragm blades in your lens disperse light. When you begin stopping down say at f8 to f25, the diffracted light is initially a small percentage of the total light that hits your sensor, but gradually, it becomes a larger percentage of the light recorded.
How this applies to Jewelry Photography
When photographing jewelry, you are using a macro lens and usual some extension tubes. When working in the macro world, DoF is quite shallow. Any of you who’ve shot flowers or insects, heck even jewelry since you are reading this, know that unless you stop-down your lens quite a bit, you will not get enough of your subject in-focus. Therefore you tend to shoot at around f11-f16, some even f22 or higher. Have you seen a sudden decrease in sharpness in your images? Well, that’s diffraction at work. The following is an example of DoF vs Defraction as applied to jewellery photography. Note: only a little sharpening was done in Capture One Pro. Additional sharpening in Photoshop improves the images a little best kitchen knives - but those affected by diffraction, win nothing in my opinion.