Botanical Photography

Markings on a typical camera lens. This symbol is the reference point for focusing distance and f-Stops The TOP ring shows the distance from the lens to the subject. In this case that is infinity. The Middle Ring shows the Depth of Focus. The red marker in the center is the reference mark for the top ring and the lowest ring. The Lowest Ring shows the f-stop (aperture) of the lens.
f-4 is great for low light situations but it lets in a lot of stray light which decreases resolution and it limits the depth of focus. Depth of focus refers to the distance behind and in front of the focal plane that will also be in focus when the picture is taken. This is not much of a consideration if you are photographing flat walls. However, most biological subjects are 3-dimensional and you usually want as much of the subject as possible to be in focus. As you focus closer to a subject, the depth of focus decreases greatly. This is a real problem with macrophotography. f-32 gives maximal depth of focus and resolution. However, it greatly restricts the amount of light that reaches the film. I always try to use f-32 for close-ups. This means that I need to use a flash or artificial light.
In this Example the lens is focused on a subject that is 0.24 meters away. Note that the top of the Red Marker points to 0.24 m. The bottom of the red marker points to f-4. This means that the aperture is wide ????? The Depth of Focus is indicated by the vertical green lines. It is extremely narrow in this case!	In this example the subject is at the same distance. However, the f-stop is 32. The Depth of Focus is indicated by the vertical green lines. Note that it is relatively large compared to the example on the left.